Hameg HM 205 User manual

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Instruments
MANUAL
Oscilloscope
HM 205

Table of contents
Oscilloscope datasheet
with technical details .......-.~.2.~.2... P 1
Accessories ..................-.. Z 1
Operating Instructions
General Information ..........0..... M 1
Use oftilthande .............0.2... M1
Safety... 0... ee ee M 1
Operating conditions ............2.2.. M 2
Guarantee ..............0..--4. M 2
Maintenance ............-.....-.. M 2
Switching over the mains/line voltage ...... M 2 .
Type of the signal voltage ..........2.. M 3 Osci I loscope
Amplitude Measurement............. M 3 HM 205
Reference Line. ................-. M 4
Time Measurements ............... M 4
Connection of Test Signal .........~.~.. M 6
First Time Operation ............... M 7
Trace Rotation .............-.-4. M8 Short instruction K 1,
DC Balance Adjustment ............. M8 Front panel elements
Probe compensation anduse........... M8 Folder with front view ............... K 2
ikHzcompensation .............. M 8
1MHzcompensation.............. M9 Test Instructions
Operating modes of the vertical amplifiers... . M10 General... 2... 2 ee T 1
X-Y Operation... 2... .0..0202.2..2.-.-.. M10 Cathode-Ray Tube: Brightness and Focus,
Phase difference measurement in DUAL mode M11 Linearity, Raster Distortions ..... T1
Measurement of an amplitude modulation... . M12 Astigmatism Check. .............-.. T 1
Triggering andtime base ............. M12 Symmetry and Drift of the Vertical Amplifier... . T 1
Automatic Triggering. ............. M12 Calibration of the Vertical Amplifier... 2... 2... T 1
Normal Triggering, Slope... ......... M13 Transmission Performance (Vertical Amplifier) . . . T 2
Triggercoupling .............-0.4 M13 Operating Modes: CHI/Il, DUAL, ADD, CHOP.,
Line Triggering ............-..... M14 INVERT and X-Y Operation... . . T 2
Triggering of video signals, External Triggering. M14 Triggering Checks ................. T3
Trigger indicator ............00.0., M15 Timebase... 2... 0-20.00. -2. 002000. T 3
Holdoff-time adjustment... ......2.2.. M15 Holdofftime .............2..2 000.4 T 4
ComponentTester................ M15 Component Tester .............-..0.0. T 4
Testpatterns ..............0..0.. M18 Trace Alignment .................. T4
Mains/Line Voltage Checks. .........2... T4
Storage Operation
Front-panelcontrols ............... M19 Service Instructions
Storage resolution and operating modes .... . M19 General... 2... .....2.2.2...2...2.-. S$ 1
Singiechanneldisplay .............. M20 Instrument Case Removal ..........2... $1
Dualdisplay............-..-2005 M21 Operating Voltages ..........-.2..2... $1
Sum and difference display. ........... M21 Maximum and Minimum Brightness ........ $1
Reference linedisplay .............. M21 Astigmatism control .. 2... .....02.2.0-. S$ 2
Timebase of low frequency signals. ....... M21 Trigger Threshold... 2... ...2.0-.-22,4 $2
Trouble-Shooting the Instrument... ....... S 2
Miscellaneous Replacement of Components and Parts ...... $3
Sawtooth output, Z-modulation input... ... . M23 Replacement of the Power Transformer ...... S$ 3
Vertical output (Y), Graticule illumination... . . M23 Adjustments .........0.....-.2004 S$ 3
Subject to change without notice 7.86 - 205

Specification
Operating Modes (Realtime and Storage)
Channel |, Channel II, Channel | and Channel II,
Channel switching: alt. and chop. (= 0.5MHz)
Sum and Difference: + CH. | + CH. II (invertable)
XY-Mode: via CH. Il and CH. | (analog only)
Vertical Deflection (Y)
Bandwidth: 2x DC to 20MHz (—3dB).
Risetime approx. 17.5ns. Overshoot: max. 1%
Deflection coefficients: 12 calibrated steps
from 5mV/cm to 20V/cem + 3% in 1-2-5 sequence,
variable 1:2.5 up to at least 2mV/cm
Input impedance: 1M || 30pF.
Input coupling: DC-AC (—3dB 4 max. 2Hz)- GD.
Input voltage: max. 400V (DC + peak AC)
Y-output from CH. 1 or CH. Il; = 45mV/cm (502)
Timebase (T)
Time coefficients (realtime): 18 calibr. steps
from 0.5us/cm to 0.2s/cm + 3% in 1-2-5 sequence,
variable 1:2.5 to max. 0.2"s/cm,
with X-expansion x 10 (+5 %) to 20ns/cm
Time coefficients (storage) 12 calibr. steps
from 1ms/cm to 5s/cm +3% in 1-2-5 sequence,
with X-expansionx10 up to 100us/cm (+ 3%)
Opt. and acoustic warning with wrong time settings.
Holdoff-time: variable up to approx. 10:1
Sawtooth output: approx. 5V (positive going)
Triggering: Automatic (= 10Hz) or normal with
Level control. LED indication at trigger action
Bandwidth: DC to 40MHz at 5mm, extern. =0.3V
Slope: positive or negative.
Sources: CH. |, CH. II, line or externally
Coupling: AC (=10Hz), DC, LF (0<1kHz),
HF (=>1,5kHz to 40MHz)
Active TV-Sync-Separator for frame and line
Horizontal deflection (X) (analog. only)
Bandwidth: DC to 2.5MHz (—3dB)
Input via CH. II (see Y deflection spec.)
X-Y phase shift: <3° from DC to 120kHz
Digital Storage
Operating modes: Refresh and Single (with Reset-
button and Ready-LED), Hold CH.1, Hold CH. II
Memory: 1024x8 bit each channel
Sampling rate: max. 100kHz 4 10us/point
Resolution: vertical 28 pts./cm, horiz. 100 pts./cm
Readout freq.: 200kHz. Picture freq.: =195Hz
X-expansion: 10fold (X-resolution: 10 pts./cm)
Option: Plotter Interface (in preparation)
Component-Tester
Test voltage: max. 8.5V,,,,. (open circuit)
Tests current: max. 24mA,,,.. (Short circuit)
Test frequency: 50 or 60Hz (line frequency).
One test lead is grounded (Safety Earth)
General Information
Cathode-ray tube: 014-364 P43/123, 8x10cem,
rect. screen, internal graticule, quick heating
Acceleration voltage: 2000V
Trace rotation: adjustable on front pane!
Z-modulation input: pos. TTL-level = bright
Graticule illumination: three-posjtion switch
Calibrator 1kHz/1 MHz (tr=3ns), 0.2V/2V + 1%
Line voltages: 110, 125, 220, 240V ~
Permissible line fluctuation: + 10%.
Line frequency range: 50-60-400Hz
Power consumption: approx. 42 Watt
Protective system: Safety Class | (IEC 348)
(Safety Class II optional.)
Weight: approx. 7.7 kg. color: techno-brown
Cabinet: W 285, H 145, D 380mm
With lockable tilt handle
Subject to change without notice
Printed in West Germany 7/86
20 MHz Oscilloscope with Digital Storage
Y:2Channels, DC to 20MHz, max. sensitivity 2mV/cm.
Tr: 0.2s-20ns/cm incl. expansion x 10. Component-Tester.
Ts: 5s-1ms/cm. Triggering up to 40 MHz; TV-Sync-Separator.
In addition to providing the impressive features of a well-designed
20 MHz real-time oscilloscope, the new HM205 permits storage and display
of slow-occurring signals and events (from 50sec to 0.1 msec). None of the
usual problems associated with long-persistence screens, such as trace flic-
ker, streaking, and relatively short view time (max. 10sec in Single-Shot mode)
due to unavoidable loss of brightness, are present in the HM205. Resolution
of 1024x256 points for the X- and Y-axes is high enough to register and display
even the most minute waveform details. In the “Refresh” mode, waveform,
amplitude, and frequency changes are visible immediately. Signals recorded in
the “Single-Shot” mode can be stored until the instrument is switched off,
even if the instrument is operated in any of its real-time modes.
The HM 205 also offers considerable ease of handling in real-time or
analog mode. One of its many impressive features is its time-tested compo-
nent tester, which operates at the touch of a single pushbutton. Another fea-
ture is the specially designed active sync separator that permits stable trig-
gering also of noisy and distorted TV signals. Triggering of other complex
signals is facilitated by the variable “Hold-Off” control. In addition, the versa-
tility of the HM205 is increased with the aid of three rear pane! BNC-sockets
for vertical signal out, sweep out, and Z-modulation input. Users taking photo-
graphs of the CRT screen will appreciate the 2 level graticule illumination.
Equally uncommon for a ‘scope in this price range is the switch-selectable
1kHz/1MHz calibrator, with a rise time of approximately 3nsec, useful for
checking gain calibration, probe compensation, and transient response from
probe tip to final amplifier.
Accessories optional
Probes 1:1, 10:1, 10:1 (HF), 100:1, 1:1/10:1; demodulating probe;
test cables BNC-BNC and Banana-BNC; 50 through termination;
adapter Banana-BNC; viewing hood; carrying case.
P1

Modular Probes
The clear advantage over ordinary probes are field replaceable
parts and the HF-compensation feature on the 10:1 attenuator pro-
bes. For the first time, probes in this price range allow adjustments
of their HF-characteristics to match individually the input imped-
ance of each scope. This is particularly important for scopes with
higher bandwidths (>50MHz), as otherwise strong overshoot or
rounding may occur, when measuring fast-rising square waves,
An exact HF-compensation, however, is only possible with square-
wave generators having a risetime <5ns. Most HAMEG scopes
already feature such a calibration generator. For other oscillo-
scopes, it is available as accessory item HZ60. At present the fol-
lowing Modular Probes are available:
Type HZ50
Attenuation Ratio ea
Bandwidth min. (MHz) 30
Risetime (ns) 11
Inp. Capacitance (pF) 45
Inp. Resistance (MQ) 1
Inp. Voltage max. (V,) 600
Cable Length (m) 1.2
Demodulator Probe
HZ51
10:1
150
<2
16
10
600
1.2
HZ52
10:1 (HF)
250
<1,4
16
10
600
1.8
HZ53
100:1
150
<2
6.5
100
1200
1.5
HZ54
selectable
1:1/10:1
10/150
35/<2
40/18
1/10
600
Td
HZ55
Special probe for AM-demodulation and wobbulator measure-
ments. HF-Bandwidth 100kHz - 500MHz (+1dB). AC Input Volt-
age 250MV - 50Vims. DC Isolation Voltage 200V DC including
peak AC. Cable length 1.2m.
Conventional Probes
These popular standard probes are well suited for all oscilloscopes
up to 20MHz bandwidth (HZ37 only with HF adjustment facility).
Typ HZ30
Attenuation Ratio 10:1
Bandwidth min. (MHz) 100
Risetime (ns) 3.5
Inp. Capacitance (pF) 13
Inp. Resistance (MQ) 10
Outp. Resistance (VQ) 1
Inp. Voltage (max. V,,) 600
Cable Length (m) 1.5
Printed in West Germany 7/86
HZ35
Vet
10
35
47
1
1
600
1.5
HZ36 H2Z37
HZ39
selectable selectable selectable
1:1/10:11:1/10:1
10/100
35/3.5
47/13
1/10
1
600
1.5
10/150
20/3.2
44/13
1/10
]
600
132
1000:1
1
50
3
500
1/10
15000
1.5
Test Cable Banana—BNC _—T HZ32
Coaxial test cable; length 1.15m, characteristic impedance 500.
Cable capacitance 120pF. Input voltage max. 500V,.
Test Cable BNC—BNC HZ34
Coaxial test cable; length 1.2m, characteristic impedance 50.
Cable capacitance 126pF. Input voltage max. 500V,.
Adapter Banana—BNC HZ20
Two 4mm binding posts (19mm between centers) to standard BNC
male plug. Input voltage max. 500V,,.
500 Through-Termination HZ22,
For terminating systems with 50 Q characteristic impedance.
Maximum load 2W. Max. voltage 10V,ms-
Carrying Cases
For HM203-1 and HM203-3 HZ42
For HM312, HM412, HM512 and HM705 HZ43
For HM307, HZ62 and HZ64 HZ44
For HM103 HZ45
For HM203-4, HM203-5, HM 203-6, HM204, HM204-2,
HM 205, HM208 and HM605 HZ46
Viewing Hood HZ47
For HM203, HM204, HM205, HM208, HM605, HM705, HM808
and HM312, HM412, HM512, HM812
Scope-Tester HZ60
For Checking the Y amplifier, timebase, and compensation of all
probes, the HZ60 is a crystal-controlled, fast rising (typ. 3ns) square-
wave generator with switchable frequencies of 1, 10, 100kHz, and
1MHz. Three BNC outputs provide signals of 25mMV,, into 502,
0.25V,, and 2.5V,,, (open circuit for 10x and 100x probes); accuracy
+1%. Battery-powered or AC supply operated (optional).
Component-Tester HZ65
Indispensable for trouble-shooting in electronic circuits. Single
component and in-circuit tests are both possible. The HZ65 oper-
ates with all scopes, which can be switched to X-Y operation (ext.
horizontal deflection). Non-destructive tests can be carried out on
almost all semiconductors, resistors, capacitors, and coils. Two
sockets provide for quick testing of the 3 junction areas in any small
power transistor. Other components are connected by using 2
banana jacks. Test leads supplied.
Examples of Test Displays:
Short circuit Capacitor 33 uF Junction E-C Z-Diode <8V
Z1

Operating Instructions
General Information .
The HM 205 is the combination of an analog (real time)
20MHz oscilloscope with a digital storage oscilloscope for
slow-speed phenomena.
This oscilloscope is easy to operate. The logical arrange-
ment of the controls allows anyone to become familiar with
the operation of the instrument after a short time, however,
experienced users are also advised to read through these
instructions so that all functions are understood.
Immediately after unpacking, the instrument should be
checked for mechanical damage and loose parts in the in-
terior. If there is transport damage, the supplier must be in-
formed immediately. The instrument must then not be put
into operation.
Check that the instrument is set to the correct mains/line
voltage. If not, refer to instructions on page M2.
Use of tilt handle
To view the screen from the best angle, there are three dif-
ferent positions (C, D, E) for setting up the instrument. If the
instrument is set down on the floor after being carried, the
handle remains automatically in the upright carrying posi-
tion (A).
In order to place the instrument onto a horizontal surface,
the handle should be turned to the upper side of the oscillo-
scope (C). For the D position (10° inclination), the handle
should be turned in the opposite direction out of the carry-
ing position until it locks in place automatically underneath
the instrument. For the E position (20° inclination), the
handle should be pulled to release it from the D position and
swing backwards until it locks once more.
The handle may also be set to a position for horizontal carry-
ing by turning it to the upper side to lock in the B position. At
the same time, the instrument must be moved upwards,
because otherwise the handle will jump back.
38
Z
Safety
This instrument has been designed: and tested in accor-
dance with IEC Publication 348, Safety Requirements for
Electronic Measuring Apparatus, and has left the factory
in a safe condition. The present instruction manual contains
important information and warnings which have to be fol-
lowed by the user to ensure safe operation and to retain the
oscilloscope in safe condition. The case, chassis and all
measuring terminals are connected to the protective earth
contact of the appliance inlet. The instrument operates ac-
cording to Safety Class I (three-conductor power cord with
protective earthing conductor and a plug with earthing con-
tact). The mains/line plug shall only be inserted in a socket
outlet provided with a protective earth contact. The protec-
tive action must not be negated by the use of an extension
cord without a protective conductor.
Warning! Any interruption of the protective conductor
inside or outside the instrument or disconnection of the
protective earth terminal is likely to make the instru-
ment dangerous. Intentional interruption of the protec-
tive earth connection is prohibited. The mains/line plug
should be inserted before connections are made to
measuring circuits.
The grounded accessible metal parts (case, sockets, jacks)
and the mains/line supply contacts (line, neutral) of the in-
strument have been tested against insulation breakdown
with 2000 Vr.m.s. (50Hz).
Under certain conditions, 50Hz or 60 Hz hum voltages can
occur in the measuring circuit due to the interconnection
with other mains/line powered equipment or instruments.
This can be avoided by using an isolation transformer
(Safety Class II) between the mains/line outlet and the
power plug of the instrument. When displaying waveforms
where the “low-level” side of the signal is at a high poten-
tial, even with the use of a protective isolation transformer,
it should be noted that this potential is connected to the os-
cilloscope’s case and other accessible metal parts. High
voltages are dangerous. In this case, special safety precau-
tions are to be taken, which must be supervised by qualified
personnel if the voltage is higher than 42V.
Most cathode-ray tubes develop X-rays. However, the
dose equivalent rate falls far below the maximum per-
missible value of 36pA/kg (0.5 mR/h}.
Whenever it is likely that protection has been impaired, the
instrument shall be made inoperative and be secured
against any unintended operation. The protection is likely to
be impaired if, for example, the instrument
— shows visible damage.
— fails to perform the intended measurements,
— has been subjected to prolonged storage under un-
favourable conditions (e.g. in the open or in moist envi-
ronments).
— has been subject to severe transport stress (e.g. in poor
packaging).
Subject to change without notice
M1

Operating conditions
The instrument has been designed for indoor use.
The permissible ambient temperature range during opera-
tion is +10°C ... +40°C. It may occasionally be subjected to
temperatures between +10°C and —10°C without degrad-
ing its safety. The permissible ambient temperature range
for storage or transportation is —40°C ... +70°C.
The maximum operating altitude is up to 2200m (non-
operating 15000m). The maximum relative humidity is up
to 80%. !
If condensed water exists in the instrument it should be
acclimatized before switching on. In some cases (e.g.
extremely cold oscilloscope) two hours should be allowed
before the instrument is put into operation. The instrument
should be kept in a clean and dry room and must not be
operated in explosive, corrosive, dusty, or moist environ-
ments. The oscilloscope can be operated in any position,
but the convection cooling must not be impaired. The ven-
tilation holes may not be covered. For continuous opera-
tion the instrument should be used in the horizontal posi-
tion, preferably tilted upwards, resting on the tilt handle.
The specifications stating tolerances are only valid if
the instrument has warmed up for 30 minutes at an
ambient temperature between +15C° and +30C°. Val-
ues not stating tolerances are typical for an average
instrument.
Guarantee
Each instrument runs through a quality test with 10 hour
burn-in before leaving the production. Practically every early
failure is detected in intermittent operation by this method.
However, it is possible that a component fails only after a
lengthy operating period. Therefore a functional guaran-
tee of 2 years is given for all units. The condition for this is
that no modifications have been made in the instrument. In
the case of shipments by post, rail or carrier it is recom-
mended that the original packing is carefully preserved.
Transport damages and damage due to gross negligence
are not covered by the guarantee.
In the case of a complaint, a label should be attached to the
housing of the instrument which describes briefly the faults
observed. If at the same time the name and telephone
number (dialing code and telephone or direct number or
department designation) is stated for possible queries, this
helps towards speeding up the processing of guarantee
claims.
Maintenance
Various important properties of the oscilloscope should be
carefully checked at certain intervals. Only in this way is it
largely certain that all signals are displayed with the accu-
racy on which the technical data are based. The test
methods described in the test plan of this manual can be
performed without great expenditure on measuring instru-
ments. However, purchase of the new HAMEG scope test-
er HZ 60, which despite its low price is highly suitable for
tasks of this type, is very much recommended.
The exterior of the oscilloscope should be cleaned regularly
with a dusting brush. Dirt which is difficult to remove on the
casing and handle, the plastic and aluminium parts, can be
removed with a moistened cloth (99% water +1% mild
detergent). Spirit or washing benzine (petroleum ether) can
be used to remove greasy dirt. The screen may be cleaned
with water or washing benzine (but not with spirit (alcohol)
or solvents), it must then be wiped with a dry clean lint-free
cloth. Under no circumstances may the cleaning fluid get
into the instrument. The use of other cleaning agents can
attack the plastic and paint surfaces.
Switching over the mains/line voltage
The instrument is set for 220 V line voltage on delivery. It
can be switched over to other voltages at the fuse holder
combined with the 3-pole appliance inlet at the rear of the
instrument. Firstly the fuse holder printed with the voltage
values is removed using a small screw driver and - if
required - provided with another fuse. Refer to the table
below for the prescribed value of the fuse. Then replace the
fuse holder so that the impressed white triangle points to
the desired voitage. Here pay attention that the cover plate
is also correctly engaged. The use of repaired fuses or short
circuiting the fuse holder is not allowed. Damage arising
because of this is not covered by the guarantee.
Fuse type: Size 5 x 20 mm; 250 V~, C;
IEC 127, Sheet lil; DIN 41 662 (possibly DIN 41 571
sheet 3).
Cutoff: time lag (T).
Line voltage Fuse rating
110V~+10% T0.63 A
1256V~+10% T0.63 A
220V ~ +10% TO.315A
240V~+10% TO.315A
M2
Subject to change without notice

Type of the signal voltage
With the HM 205, practically all periodically repeating sig-
nals with the frequency spectrum below 20 MHz can be
examined in the analog real time mode. (Because of the
limited scanning rate, other limits which are further influ-
enced by signal shape and screen amplitude apply in the
digital memory mode.) The display of simple electrical pro-
cesses, such as sinusoidal RF and LF signals or line fre-
quency hum voltages is straightforward. When recording
square-wave or pulse-type signal voltages, it must be noted
that their harmonics must also be transmitted. The repeti-
tion frequency of the signal must therefore be significantly
smaller than the upper limit frequency of the vertical
amplifier. Accurate evaluation of such signals is only possi-
bie up to approximately 2 MHz repetition frequency. Dis-
playing composite signals can be difficult, especially if they
contain no repetive higher amplitude content which can be
used for triggering. This is the case with bursts, for
instance. To obtain a well-triggered display in this case, the
assistance of the variable holdoff and/or variable time con-
trol may be required. Television video signals are rela-
tively easy to trigger using the built-in TV-Syne-Separator
with correct trigger slope setting.
For optional operation as a DC or AC voltage amplifier, the
vertical amplifier input is provided with a DC/AC switch.
The DC position should only be used with a series-con-
nected attenuator probe or at very low frequencies or if the
measurement of the DC voltage content of the signal is
absolutely necessary.
When displaying very low frequency pulses, the flat tops
may be sloping with AC coupling of the vertical amplifier
(AC limit frequency approx. 1.6 Hz for —3dB). In this case,
DC operation is preferred, provided the signal voltage is not
superimposed on a too high DC level. Otherwise a capacitor
of adequate capacitance must be connected to the input of
the vertical amplifier with DC coupling. This capacitor must
have a sufficiently high breakdown voltage rating. DC cou-
pling is also recommended for the display of logic and pulse
signals, especially if the pulse duty factor changes con-
stantly. Otherwise the display will move upwards or down-
wards at each change. Pure direct voltages can only be
measured with DC-coupling.
Amplitude Measurements
In general electrical engineering, alternating voltage data
normally refers to effective values (rms = root-mean-
square value). However, for signal magnitudes and voltage
designations in oscilloscope measurements, the peak-to-
peak voltage (V,,) value is applied. The latter corresponds to
the real potential difference between the most positive and
most negative points of a signal waveform.
If a sinusoidal waveform, displayed on the oscilloscope
screen, is to be converted into an effective (rms) value, the
resulting peak-to-peak value must be divided by 2xV¥ 2 =
2.83. Conversely, it should be observed that sinusoidal volt-
ages indicated in V, 5 (Ver) have 2.83 times the potential dif-
ference in V,,. The relationship between the different volt-
age magnitudes can be seen from the following figure.
Voltage values of a sine curve
Vims = effective value; V, = simple peak or crest value;
Vop = peak-to-peak value; Vinom = Momentary value.
The minimum signal voltage required at the vertical
amplifier input for a display of 1 cm is approximately 2mvV,,,.
This is achieved with the attenuator control set at5mV/cm,
its variable control in the fully clockwise position. How-
ever, smaller signals than this may also be displayed. The
deflection coefficients on the input attenuators are indi-
cated in mV/cm or V/cm (peak-to-peak value).
The magnitude of the applied voltage is ascertained by
multiplying the selected deflection coefficient by the
vertical display height in cm.
if an attenuator probe x 10 is used, a further muftiplica-
tion by a factor of 10 is required to ascertain the correct
voltage value.
For exact amplitude measurements, the variable con-
trol on the attenuator switch must be set to its calibra-
ted detent CAL. When turning the variable control cw,
the sensitivity will be increased by a factor of 2.5.
Therefore every intermediate value is possible within
the 1-2-5 sequence.
With direct connection to the vertical input, signals up to
160V,,, may be displayed (attenuator set to 20V/cm, vari-
able control ccw).
With the designations
H = display height in cm,
U = signal voltage in V,, at the vertical input,
D = deflection coefficient in V/cm at attenuator switch,
the required quantity can be calculated from the two given
quantities:
U = D-H p = ¥
Subject to change without notice
M3 205

However, these three values are not freely selectable. They
have to be within the following limits (trigger threshold,
accuracy of reading):
H between 0.5 and 8cm, if possible 3.2 to 8cm,
U between 2.5mV,, and 160V,,,
D between 5mV/cm and 20V/cm in 1-2-5 sequence.
Examples:
Set deflection coefficient D = 50mV/cm & 0.05 V/cm,
observed display height H = 4.6 cm,
required voltage U = 0.05-4.6 = 0.23 V,,.
Input voltage U = 5V,,,
set deflection coefficient D = 1 V/cm,
required display height H = 5:1 = 5cm
Signal voltage U = 220Vims*2-V2 = 622 Vp,
(voltage > 160V,,, with probe x 10:U = 62.2 V,,),
desired display height H = min. 3.2cm, max. 8cm,
max. deflection coefficient D = 62.2:3.2 = 19.4V/cm,
min. deflection coefficient D = 62.2:8 = 7.8V/cm,
adjusted deflection coefficient D = 10V/cm
if the applied signal is superimposed on a DC (direct
voltage) level the total value (DC + peak value of the
alternating voltage) of the signal across the Y-input
must not exceed +400V (see figure). This same limit
applies to normal x10 attenuator probes, the attenuation
ratio of which allows signal voltages up to approximately
1,000V,, to be evaluated. Voltages of up to approximately
2,400V,, may be measured by using the HZ53 high voltage
probe which has an attenuation ratio of 100:1. It should be
noted that its AC,,., value is derated at higher frequencies.
If a normal x10 probe is used to measure high voltages
there is the risk that the compensation trimmer bridging the
attenuator series resistor will break down causing damage
to the input of the oscilloscope. However, if for example
only the residual rippie of a high voltage is to be displayed on
the oscilloscope, a normal x10 probe is sufficient. In this
case, an appropriate high voltage capacitor (approx. 22-
68nF) must be connected in series with the input tip of the
probe.
Voltage
DC + ACpcak = 400 Vinax.
Total value of input vottage
The dotted line shows a voltage alternating at zero voit level. When superim-
posed a DC level, the addition of the positive peak and the DC voltage results
in the max. voltage (DC + AC,,..).
It is very important that the oscilloscope input coupling is
set to DC, if an attenuator probe is used for voltages higher
than 400V (see page M5: Connection of Test Signal).
Reference Line
With Y-POS. control (input coupling to GD) it is possible to
set a horizontal graticule line as reference line for ground
potential before the measurement. It can lie below or
above the horizontal central line according to whether posi-
tive and/or negative deviations from the ground poterntial
are to be measured. Certain switchable x10/x1 attenuator
probes also have a built-in ground reference switch posi-
tion.
Time Measurements
As a rule, most signals to be displayed are periodically
repeating processes, also called periods. The number of
periods per second is the repetition frequency. Depending
on the time base setting of the TIME/DIV. switch, one or
several signal periods or only a part of a period can be dis-
played. The time coefficients are stated in s/em, ms/cm
and us/em on the TIME/DIV.-switch. The scale is accord-
ingly divided into three fields.
There are 18 time coefficient ranges in the analog real time
mode of the HM 205, from 0.5us/em to 0.2ms/em. The
limit ranges are indicated by black dashed lines. The ranges
are overlapped with 12 time coefficient ranges of the stor-
age mode, from 1ms/cm to 5s/em. The storage ranges
are outlined in black and marked with STOR. under the
scale.
With the pushbutton STOR. ON in the X-field, the HM 205
may be switched over from real time to storage operation
and vice versa. In each operating mode, the TIME/DIV.
switch should be set correctly; if not, the STOR. ON LED
immediately starts with blinking and a piezo beeper gives
intermittent acoustic alarm.
The duration of a signal period or a part of it is deter-
mined by multiplying the relevant time (horizontal dis-
tance in cm] by the time coefficient set on the TIME/
DIV.-switch.
The variable time control (identified with an arrow
knob cap) must be in its calibrated position CAL. (arrow
pointing horizontally to the left). This variable control is
inoperative in the storage mode.
With the designations
L =displayed wave length in cm of one period,
T = time in seconds for one period,
F =recurrence frequency in Hz of the signal,
T, = time coefficient in s/em on timebase switch and
the relation F = 1/T, the following equations can be stated:
M4 205 Subject to change without notice

— . => T = T
T=L-T, L= 2 t=
- 1. = - _1_
F= oh L = £7, he OF
With depressed X-MAG. x10 pushbutton the T, value
must be divided by 10.
However, these four values are not freely selectable. They
have to be within the following limits:
between 0.2 and 10cm, if possible 4 to 10cm,
between 0.05 us and 2s,
between 0.5 Hz and 20 MHz,
¢ between 0.5us/cm and 0.2s/cm in 1-2-5 sequence
(with X-MAG. x 10 in out position), and
T, between 50ns/cm and 20ms/cm in 1-2-5 sequence
(with pushed X-MAG. x10 pushbutton).
an746
Examples:
Displayed wavelength L = 7cm,
set time coefficient T, = 0.5us/cm,
required period T = 7-0.5-10-° = 3.5us
required rec. freq. F = 1:(3.5- 107°) = 286 kHz.
Signal period T = 0.5s,
set time coefficient T, = 0.2s/cm,
required wavelength L = 0.5:0.2 = 2.5cm.
Displayed ripple wavelength L = 1cm,
set time coefficient T, = 10ms/cm,
required ripple freq. F = 1: (1-10-107) = 100Hz.
TV-line frequency F = 15 625Hz,
set time coefficient T, = 10us/cm,
required wavelength L = 1:(15 625-107°) = 6.4cm.
Sine wavelength L = min. 4cm, max. 10cm,
Frequency F = 1kHz,
max. time coefficient T, = 1: (4-10°) = 0.25 ms/cm,
min. time coefficient T, = 1:(10-103) = 0.1 ms/cm,
set time coefficient T, = 0.2ms/cm,
required wavelength L = 1:(10°-0.2-1079) = 5em.
Displayed wavelength L = 0.8cm,
set time coefficient T, = 0.5s/cm,
pressed X-MAG. x10 button: T, = 0.05us/cm,
required rec. freq. F = 1:(0.8-0.05-10-°) = 25 MHz,
required period T = 1:(25-10°) = 40 ns.
If the time is relatively short as compared with the complete
signal period, an expanded time scale should always be
applied (X-MAG. x10 button pressed). In this case, the
ascertained time values have to be divided by 10. The time
interval of interest can be shifted to the screen center using
the X-POS. control.
When investigating pulse or square waveforms, the critical
feature is the risetime of the voltage step. To ensure that
transients, ramp-offs, and bandwidth limits do not unduly
infiuence the measuring accuracy, the risetime 's generally
measured between 10% and 90% of the vertical pulse
height. For peak-to-peak signal amplitude of 5em height,
which are symmetrically adjusted to the horizontal center
line, the internal graticule of the CRT has two horizontal dot-
ted lines +2.5cm from the center line. Adjust the Y
attenuator switch with its variable control together with the
Y-POS. control so that the pulse height is precisely aligned
with these 0 and 100% lines. The 10% and 90% points of
the signal will now coincide with the two lines, which have
a distance of +2cm from the horizontal center line and an
additional subdivision of 0.2cm. The risetime is given by
the product of the horizontal distance in cm between
these two coincidence points and the time coefficient
setting. \f magnification is used, this product must be
divided by 10. The fall time of a pulse can also be measured
by using this method.
The following figure shows correct positioning of the oscil-
loscope trace for accurate risetime measurement.
PETTT
opt
With a time coefficient of 0.5us/em and pushed X-MAG
x10 button the example shown in the above figure results
in a measured total risetime of
tit = 1.6cm-0.5us/em: 10 = 80ns
When very fast risetimes are being measured, the rise-
times of the oscilloscope amplifier and of the attenuator
probe has to be deducted from the measured time value.
The risetime of the signal can be calculated using the fol-
lowing formula.
t, =| tro? ~ tose” _ t,?
in this t,o; is the total measured risetime, t,,, is the risetime
of the oscilloscope amplifier (approx. 17,5ns), and t, the
risetime of the probe (e.g. = 2ns). If t,, is greater than
100ns, then t,,, can be taken as the risetime of the pulse,
and calculation is unnecessary.
Calculation of the example in the figure above results in a
signal risetime
t,=V 802 — 17.5% — 2° = 78.04ns
Subject to change without notice
M5 205

The measurement of the rise or fall time is not limited to the
trace dimensions shown in the above diagram. It is only par-
ticularly simple in this way. In principle it is possible to
measure in any display position and at any signal amplitude.
It is only important that the full height of the signal edge of
interest is visible in its full length at not too great steepness
and that the horizontal distance at 10% and 90% of the
amplitude is measured. !f the edge shows rounding or over-
shooting, the 100% should not be related to the peak val-
ues but to the mean pulse heights. Breaks or peaks
(glitches) next to the edge are also not taken into account.
With very severe transient distortions, the rise and fall time
measurement has little sense. For amplifiers with approxi-
mately constant group delay (therefore good pulse trans-
mission performance) the following numerical relationship
between rise time tr (in ns) and bandwidth B (in MHz)
applies:
Connection of Test Signal
Caution: When connecting unknown signals to the oscillo-
scope input, always use automatic triggering and set the
DC-AC input coupling switch to AC. The attenuator switch
should initially be set to 20V/cm.
Sometimes the trace will disappear after an input signal has
been applied. The attenuator switch must then be turned
back to the left, until the vertical signal height is only 3-8cm.
With a signal amplitude greater than 160V,,, an attenuator
probe must be inserted before the oscilloscope’s vertical
input. If, after applying the signal, the trace is nearly
blanked, the period of the signal is probably substantially
longer than the set value on the TIME/DIV. switch. It
should be turned to the left to an adequately larger time
coefficient.
The signal to be displayed can be connected directly to the
Y-input of the oscilloscope with a shielded test cable such
as HZ 32 and HZ 34 or attenuated through a x10 or x100
attenuator probe. The use of test cables with high imped-
ance circuits is only recommended for relatively low fre-
quencies (up to approx. 50 kHz). For higher frequencies, the
signal source must be of low impedance, i.e. matched to
the characteristic resistance of the cable (as a rule 50 Ohm).
Especially when transmitting square and pulse signals, a
resistor equal to the characteristic impedance of the cable
must also be connected across the cable directly at the Y-
input of the oscilloscope. When using a 50 Ohm cable such
as the HZ 34, a 50 Ohm through termination type HZ 22 is
available from HAMEG. When transmitting square signals
with short rise times, transient phenomena on the edges
and top of the signal may become visible if the correct ter-
mination is not used. A terminating resistance is some-
times recommended with sine signals as well. Certain
amplifiers, generators or their attenuators maintain the
nominal output voltage independent of frequency only if
their connection cable is terminated with the prescribed
resistance. Here it must be noted that the terminating resis-
tor HZ 22 will only dissipate a maximum of 2 Watts. This
power is reached with 10 V,,5 or — at 28.3 V,, with sine sig-
nal.
If a x10 or x100 attenuator probe is used, no termination is
necessary. In this case, the connecting cable is matched
directly to the high impedance input of the oscilloscope.
When using attenuators probes, even high internal imped-
ance sources are only slightly loaded (approx. 10 MQ Il 16
pF or 100 MQ II 7 pF with HZ 53). Therefore, if the voltage
loss due to the attenuation of the probe can be compen-
sated by a higher amplitude setting, the probe should
always be used. The series impedance of the probe pro-
vides a certain amount of protection for the input of the ver-
tical amplifier. Because of their separate manufacture, all
attenuator probes are only partially compensated, therefore
accurate compensation must be performed on the oscillo-
scope (see “Probe compensation” page M8).
Standard attenuator probes on the oscilloscope normally
reduce its bandwidth and increase the rise time. In all cases
where the oscilloscope band width must be fully utilized
(e.g. for pulses with steep edges) we strongly advise using
the modular probes HZ 51 (x10) HZ 52(x10 HF) and HZ 54
or HZ 37 (x1 and x10) (see oscilloscope accessories, page
Z1). This can save the purchase of an oscilloscope with
larger bandwidth and has the advantage that defective com-
ponents can be ordered from HAMEG and replaced by one-
self. The probes mentioned have a HF-calibration in addition
to low frequency calibration adjustment. Thus a group delay
correction to the upper limit frequency of the oscilloscope is
possible with the aid of the calibrator built into the instru-
ment switched to 1 MHz. In fact the bandwidth and rise
time of the oscilloscope are not noticably changed with
these probe types and the waveform reproduction fidelity
can even be improved because the probe can be matched
to the oscilloscope’s individual pulse response.
if ax10 or x100 attenuator probe is used, DC input cou-
pling must always be used at voltages above 400 V.
With AC coupling of low frequency signals, the attenuation
is no longer independent of frequency, pulses can show
pulse tilts. Direct voltages are suppressed but load the oscil-
loscope input coupling capacitor concerned. Its voltage rat-
ing is max. 400 V (DC + peak AC). DC input coupling is
therefore of quite special importance with a x100 attenua-
tion probe which usually has a voltage rating of max. 1200
V (DC + peak AC). A capacitor of corresponding capaci-
tance and voltage rating may be connected in series with
M6 205
Subject to change without notice

the attenuator probe input for blocking DC voltage (e.g. for
hum voltage measurement).
With all attenuator probes, the maximum AC input vott-
age must be derated with frequency usually above 20 kHz.
Therefore the derating curve of the attenuator probe type
concerned must be taken into account.
The selection of the ground point on the test object is impor-
tant when displaying small signal voltages. It should always
be as close as possibile to the measuring point. If this is not
done, serious signal distortion may result from spurious cur-
rents through the ground leads or chassis parts. The ground
leads on attenuator probes are also particularly critical. They
should be as short and thick as possible. When the
attenuator probe is connected to a BNC-socket, a BNC-
adapter, which is often supplied as probe accessory, should
be used. In this way ground and matching problems are
eliminated.
Hum or interference appearing in the measuring circuit
(especially when a small deflection coefficient is used) is
possibly caused by multiple grounding because equalizing
currents can flow in the shielding of the test cables (voltage
drop between the protective conductor connections,
caused by external equipment connected to the mains/line,
e.g. signal generators with interference protection
capacitors).
First Time Operation
Check that the instrument is set to the correct mains/
line voltage. (Refer to page M2).
Before applying power to the oscilloscope it is recom-
mended that the following simple procedures are per-
formed:
— Check that all pushbuttons are in the out position, i.e.
released.
— Rotate the four variable controls with arrows, i.e. TIME/
DIV. variable control, CH.L and CH.II attenuator variable
controls, and HOLD OFF control fully counter-clockwise
to their calibrated detent.
— Set all controls with marker lines to their midrange posi-
tion (marker lines pointing vertically).
— The TV SEP. lever switch and the TRIG. selector lever
switch in the X-field should be set to their uppermost
position.
— Both DC-AC-GD input coupling slide switches for CH. 1 and
CH. Il in the Y-field should be set to the GD position.
Switch on the oscilloscope by depressing the red POWER
pushbutton. An LED will illuminate to indicate working
order. The trace, displaying one baseline, should be visible
after a short warm-up period of 10 seconds. Adjust Y-POS.!
and X-POS. controls to center the baseline. Adjust
INTENS. (intensity) and FOCUS controls for medium
brightness and optimum sharpness of the trace. The oscillo-
scope is now ready for use.
If only a spot appears (CAUTION! CRT phosphor can be
damaged.), reduce the intensity immediately and check
that the X-Y pushbutton is in the released (out) position. tf
the trace is not visible, check the correct positions of all
knobs and switches (particularly AT/NORM. button in out
position).
To obtain the maximum life from the cathode-ray tube, the
minimum intensity setting necessary for the measurement
in hand and the ambient light conditions should be used.
Particular care is required when a single spot is dis-
played. as a very high intensity setting may cause damage
to the fluorescent screen of the CRT. Switching the oscillo-
scope off and on at short intervals stresses the cathode of
the CRT and should therefore be avoided.
The instrument is so designed that even incorrect operation
will not cause serious damage. The pushbuttons control
only minor functions, and it is recommended that before
commencement of operation all pushbuttons are in the
“out” position. After this the pushbuttons can be operated
depending upon the mode of operation required.
The HM 205 accepts all signals frorn DC (direct voltage) up
to a frequency of at least 20 MHz (-3dB). For sinewave volt-
ages the upper frequency limit will be 30-35 MHz.
However, in this higher frequency range the vertical display
height on the screen is limited to approx. 4-5cm. The time
resolution poses no problem. For example, with 25MHz
and the fastest adjustable sweep rate (20ns/cm), one cycle
will be displayed every 2cm. The tolerance on indicated val-
ues amounts to +3% in both deflection directions. All val-
ues to be measured can therefore be determined relatively
accurately. However, from approximately 6MHz upwards
the measuring error will increase as a result of loss of gain.
At 12MHz this reduction is about 10%. Thus, approxi-
mately 11% should be added to the measured voltage at
this frequency. As the bandwidth of the amplifiers differ
(normally between 20 and 25 MHz), the measured values in
the upper limit range cannot be defined exactly. Addition-
ally, as already mentioned, for frequencies above 20 MHz
the dynamic range of the display height steadily decreases.
The vertical amplifier is designed so that the transmission
performance is not affected by its own overshoot.
Subject to change without notice
M7 205

Trace Rotation TR
in spite of Mumetal-shielding of the CRT, effects of the
earth’s magnetic field on the horizontal trace position
cannot be completely avoided. This is dependent upon
the orientation of the oscilloscope on the place of work.
A centred trace may not align exactly with the horizon-
tal center line of the graticule. A few degrees of mis-
alignment can be corrected by a potentiometer acessi-
ble through an opening on the front panel marked TR.
DC Balance Adjustment
The vertical preamplifiers for CH.l and CHI contain
matched dual FETs connected as input source followers.
After long periods of use the FET characteristics may
change which can alter the DC balance of the vertical
amplifier.
A quick check can be made on each channel by rotating the
variable control knob on the attenuator switch to and fro,
clockwise and back to the calibrated detent CAL. If the trace
moves from the vertical position (up or down) more than
1mm, the DC balance will require readjustment. This check
should be made after a 20 minute warm-up period.
Adjustment procedure
The following instructions should be performed to obtain
the correct DC balance adjustment of both channels.
— Remove all input cables and adjust oscilloscope controls
to display the baseline.
— Center the baseline using Y-POS. and X-POS. controls.
— Set attenuator switches to 5mV/em and input coupling
switches to GD.
— Release all pushbuttons in the Y-field.
— Place the oscilloscope so that it rests firmly on its back (up-
right position) and locate DC balance adjustment poten-
tiometer access holes — marked CH.f DC-BALANCE
CH.H — which are found underneath the instrument.
— Insert a screwdriver (blade approx. 3mm, length min.
20mm) in CH.I hole. A plastic guide with slotted bottom
is located behind the hole.
— Rotate VOLTS/DIV. variable control to and fro and
adjust balance pot so that the baseline no longer moves
up or down. When the trace remains steady, correction
of CH.I is completed.
— Depress CHVII button. Repeat adjustment procedure
for CH.IL
Probe compensation and use
The attenuator probe must be matched exactly to the input
impedance of the vertical amplifier to ensure an undistorted
display of waveforms. A switchable generator built into the
HM 205 supplies a square wave signal for this purpose with
very short rise time (<5 ns) at 1 kHz or 1 MHz frequency,
selected by pushbutton. The square wave signal can be
taken from the two concentric sockets beneath the screen.
One socket supplies 0.2V,, +1% for x10 attenuator
probes, the other 2V,, +1% for x100 attenuator probes.
These voltages correspond in each case to a screen
amplitude of 4 em provided the input attenuator switch of
the HM 205 is set to the deflection coefficient 5 mV/cem.
The internal diameter of the sockets is 4.9 mm and corres-
ponds directly to the (grounded) external diameter of the
shielding tube of modern modular probes and probes of
the series F (internationally standardized). This is the only
way to produce an extremely short ground connection
which is essential for high signal frequencies and an undis-
torted wave form display of non-sinusoidal signals.
1 kHz compensation
This trimmer adjustment compensates the capacitive load-
ing of the oscilloscope input (approx. 30 pF for the HM 205).
After compensation, the capacitive attenuation has the
same attenuation ratio as the ohmic divider. The same volt-
age attenuation then results at high and low frequencies as
for direct voltage (for x1 probes or probes switches over to
x1, this compensation is neither necessary nor possible).
The trace line must be parallel with the horizontal graticule
lines (see “Trace rotation TR”, page M8).
Connect attenuator probe (type HZ 51, 52, 53, 54 or also HZ
36 and HZ 37) to the CH.I input, do not press any buttons or
turn any knobs, set input coupling to DC, input attenuator to
5 mV/em and TIME/DIV. switch to 0.2 ms/em (both vari-
able controls in calibration position CAL.), insert probe
(without spring hook) into the corresponding CAL. socket
-(x10 probe in 0.2 V socket, x100 in 2 V socket).
1kHz
incorrect incorrect correct
3 corners can be seen on the screen. The compensation
trimmer must now be adjusted. It is generally located in the
probe itself. It is located in the x100 attenuator probe HZ 53
in the small box on the BNC plug. Adjust the trimmer with
the insulating screw driver provided until the tops of the
square wave signal are exactly parallel to the horizontal
graticule lines (see 1 kHz diagram). The signal height should
then be 4cm +1.2 mm (= 3 %). The signal edges are invis-
ible during this adjustment.
M8 205
Subject to change without notice

1 MHz compensation
HF adjustment is possible for the HZ37, 51, 52, and 54
probes. These possess resonance correction elements
(pots in combination with coils and capacitors) with which it
is possible for the first time to simply adjust the probe in the
upper frequency range of the vertical amplifier.
After this compensation, not only the maximum possible
bandwidth is obtained in the attenuator probe mode but
also a largely constant group delay at the end of the
bandwidth. In this way transient distortions (such as over-
shooting, rounding off, ringing, holes or humps in the pulse
top) in the vicinity of the leading edge are kept to a
minimum. The bandwidth of the HM 205 is therefore fully
utilized when using the HZ37, 51, 52 and 54 probes without
having to accept wave form distortions.
Prerequisite for this HF compensation is a square wave
generator with short rise time (typically 4 ns) and low-
impedance output (approx. 50 Ohm) which also supplies a
voltage of 0.2 V or 2 V at a frequency of 1 MHz.
The calibrator output of the HM 205 fulfills these conditions
when the 1 MHz button is depressed.
Connect probes of the said types to the CH.I input, press
only 1 MHz calibrator button, set input coupling to DC, input
attenuator to5 mV/cm and TIME/DIV. switch to 0.2 us/em
(both fine controls in calibration position CAL.). Insert probe
in 0.2 V socket. The square-wave edges are now visible on
the screen.
The leading edge and the upper left pulse top corner should
be observed.
Remove the insulating cap (or, with HZ37, the anti-kink
device) directly behind the BNC plug of the attenuator probe
(hold cap, unscrew cable strain relief union nut, withdraw
insulating cap from the BNC plug, screw back union nut
with cable}. One slotted trimmer screw is visible with the
types HZ37, HZ51, and HZ54 in the box behind the BNC
plug, and 3 slotted screws in the type HZ52.
Adjust the upper left pulse top for optimum with these.
Neither overshooting nor rounding off is allowable. This is
quite simple for HZ37, 51, and 54, but somewhat more dif-
ficult for the x10 HF probe HZ 52 with 3 trimmers.
In this case it is possible to adjust the leading edge steep-
ness and to straighten out aberrations in the pulse top
directly next to the leading edge. The leading edge should
be as steep as possible but the top as straight as possible.
HF compensation is simplified in that the 3 trimmers each
possess a defined area of influence (see the following draw-
ings). The start of the pulse top is clearly visible with the X-
MAG. x10 button depressed.
Adjusting points of the probes
HZ37, HZ51, HZ54
Bl sp |) Ciclo TI o
Osc. CAL.
T, (HF)
(LF) T,
—— 10ns/cm
HF
T, (LF)
T3: Influence on the medium frequencies
T4: Influence on the leading edge
T5: Influence on the lower frequencies
After completion of HF compensation, check the signal
height on the screen at 1 MHz as well. It should have the
same value as stated above for the 1 kHz compensation.
Now refit the insulating cap to the BNC plug.
oe:
a es an ie
Adjustment
TMHz
Attentuator probes other than those mentioned above gen-
erally have larger probe diameters and do not fit into the cal-
ibrator sockets. It is not difficult for a good technician to
make a Suitable adapter for this. However, we would point
out that such attenuator probes usually have a too long rise
time so that the total bandwidth of oscilloscope with
Subject to change without notice
M9 205

he
SSS
SSS
SSS
SS
SSS
St
SSS
SSS
SS
attenuator probe is far below that of the HM 205. Also these
probes do not normally have compensation facilities. There-
fore, wave form distortions cannot be excluded at high
repetition frequencies.
It is important that the sequence of firstly 1 kHz and then 1
MHz compensation must be followed but need not be
repeated, also calibrator frequencies of 1 kHz and 1 MHz
cannot be used for time calibration. The pulse duty factor
also deviates from the value 1: 1. Short rise time, horizontal
pulse tops, calibrated pulse height and zero potential at the
pulse bottom are essential for exact attenuator probe com-
pensation. Frequency and pulse duty factor are not critical
here.
Low pulse rise time and low-impedance generator output
are particularly important for assessing the transmission
performance. The calibrator of the HM 205 can even
replace expensive square wave generators with these
properties and the switchable frequency, e.g. when cali-
brating wideband attenuators or in the assessment of wide-
band amplifiers.
The test circuit can be connected via a suitable probe from
one of the HM 205 CAL. sockets. Plug the probe tip into the
0.2V output socket. Select either 1kHz or 1 MHz output fre-
quency. If your circuit has a high input impedance (e.g.
1MQI115-5O0pF minimum) then use an attenator probe
such as x10 or x100. The applied signal will then be the CAL.
output divided by the probe attenuation e.g. 0.2V:10 =
20 mV etc. HAMEG probes type HZ37, 51, 52, HZ53 and 54
are suitable for this application. However if your circuit has
a low input impedance (e.g. 502), a x1 probe can be used
{in this case use a 50Q termination). The HAMEG HZ37,
HZ50, and HZ54 (x1 position) probes are suitable. The
switchable probes must be switched over to x1 and their HF
trimmer beneath the insulating cap of the BNC plug set to
the left stop. Approx. 40 mV,, is then obtained at the circuit
input (at 50 Ohm) with the HZ50 and approx. 17 and 24
MV,» With the HZ37 and 54, when the probe is inserted in
the 0.2 V CAL. socket. The voltage values stated here have
a tolerance larger than 1 % because 50 Ohm loading is not
normal for such a probe. Using the 2 V CAL. socket under
the same conditions is possible only with the HZ37 and
H2Z54. Then approx. 180 mV,, is obtained at 50 Ohm, with
around twice the normal rise time. More accurate voltage
values in the x1 mode can be measured immediately with
the HM 205 if a 50 Ohm through-termination HZ22 is con-
nected directly between the BNC plug output of the probe
and the Y input of the oscilloscope.
Operating modes of the vertical amplifiers
The desired operating mode of the vertical amplifiers is
selected with the 3 buttons in the Y field. All three buttons
out for mono mode. Only Channel lis then operational. The
button CH I/il-TRIG.V/I must be depressed in mono mode
for Channel Il. The internal triggering is simultaneously
switched over to Channel fl with this button.
If the DUAL button is depressed, both channels are work-
ing. Two signals can be displayed together in this button
position (alternate mode). This mode is not suitable for dis-
playing very slow-running processes. The display then flick-
ers too much or it appears to jump. If the CHOP. button is
depressed in addition to DUAL, both channels are switched
over constantly at a high frequency within a sweep period
(CHOP mode). Slow running processes below 1 kHz or
with time coefficients higher than 1ms/cm are then also
displayed without flicker. The dual mode chosen is less
important for signals with higher repetition frequency.
If the ADD button is depressed, the signals of both chan-
nels are algebraically added (+ | + II). Whether the resulting
display shows the sum or difference is dependent on the
phase relationship or the polarity of the signals and on the
positions of both INVERT buttons.
In-phase input voltages:
Both INVERT buttons released = sum.
Both INVERT buttons depressed = sum.
Only one INVERT button depressed = difference.
Antiphase input voltages:
Both INVERT buttons released = difference.
Both INVERT buttons depressed = difference.
Only one INVERT button depressed = sum.
In the ADD mode the vertical display position is dependent
upon the Y-POS. setting of both channels. The same
attenuator switch position is normally used for both chan-
nels with algebraic addition.
Differential measurement techniques allow direct meas-
urement of the voltage drop across floating components
(both ends above ground). Two identical probes should be
used for both vertical inputs. Using a separate ground con-
nection and not connecting the probe or cable shields to the
circuit under test avoid ground loops (hum, common-mode
disturbances).
X-Y Operation
For X-Y operation, the pushbutton in the X field marked X-Y¥
must be depressed. The X signal is then derived from the
Channel i (HOR. INP.). The calibration of the X signal
during X-Y operation is determined by the setting of
the Channel Il input attenuator and variable control.
This means that the sensitivity ranges and input imped-
ances are identical for both the X and Y axes. However, the
M10 205
Subject to change without notice

Y-POS.H control is disconnected in this mode. Its function
is taken over by the X-POS. control. It is important to note
that the X-MAG. x10 facility, normally used for expanding
the sweep, should not be operated in the X-Y mode. It
should also be noted that the bandwidth of the X amplifier
is approximately 2.5 MHz {(-3dB), and therefore an increase
in phase difference between both axes is noticeable from
50 kHz upwards.
The Y-Input signal may be inverted by using the INVERT
facility. However, the inversion of the X-input signal using
the CH. li INVERT button is not possibie.
Lissajous figures can be displayed in the X-Y mode for cer-
tain measuring tasks:
— Comparing two signals of different frequency or bringing
one frequency up to the frequency of the other signal.
This also applies for whole number multiples or fractions
of the one signal frequency.
— Phase comparison between two signals of the same fre-
quency.
Phase comparison with Lissajous figure
The following diagrams show two sine signals of the same
frequency and amplitude with different phase angles.
PL BO
| | |
Calculation of the phase angle or the phase shift between
the X and Y input voltages (after measuring the distances a
and b on the screen) is quite simple with the following for-
mula and a pocket calculator with trigonometric functions
and besides independent of both deflecting amplitudes
on the screen.
sing = 5
a\2
cos g = -\b
a
9” = arc sin |
The following must be noted here:
— Because of the periodic nature of the trigonometric func-
tions, the calculation should be limited to angles <90°.
However here is the advantage of the method.
— Do not use a too high test frequency. The phase shift of
the two oscilloscope amplifiers of the HM 205 in the X-Y
mode can exceed an angle of 3° above 120 kHz.
— It cannot be seen as a matter of course from the screen
display if the test voltage leads or lags the reference volt-
age. A CR network before the test voltage input of the
oscilloscope can help here. The 1 MQ input resistance
can equally serve as R here, so that only a suitable
capacitor C needs to be connected in series. If the aper-
ture width of the ellipse is increased (compared with C
short-circuited), then the test voltage leads the refer-
ence voltage and vice versa. This applies only in the reg-
ion up to 90° phase shift. Therefore C should be suffi-
ciently large and produce only a relatively small just
observable phase shift.
Should both input voltages be missing or fail in the X-Y
mode, a very bright light dot is displayed on the screen.
This dot can burn into the phosphor at a too high
brightness setting (INTENS. knob) which causes either
a lasting loss of brightness, or in the extreme case,
complete destruction of the phosphor at this point.
Phase difference measurement
in DUAL mode
A larger phase difference between two input signals of
the same frequency and shape can be measured very sim-
ply on the screen in Dual mode (DUAL button depressed).
The time base should be triggered by the reference signal
(phase position 0). The other signal can then have a leading
or lagging phase angle. Alternate mode should be selected
for frequencies =1 kHz; the Chop mode is more suitable
for frequencies <1 kHz (less flickering). For greatest accu-
racy adjust not much more than one period and approxi-
mately the same height of both signals on the screen. The
variable controls for amplitude and time base and the
LEVEL knob can also be used for this adjustment — without
influence on the result. Both base lines are set onto the hori-
zontal graticule center line with the Y-POS. knobs before
the measurement. With sinusoidal signals, observe the
zero (crossover point) transitions; the sine peaks are less
accurate. If a sine signal is noticably distorted by even har-
monics, or if an offset direct voltage is present, AC coupling
is recommended for both channels. If it is a question of
pulses of the same shape, read off at steep edges.
Phase difference measurement in dual mode
t = horizontal spacing of the zero transitions in cm.
T = horizontal spacing for one period in cm.
Subject to change without notice
M11 205

ee
EEE
ERR
ae
In the example illustrated, tf = 3cm and T = 10cm. The
phase difference in degrees is calculated from
t 3
9 = 7 960° =~, 360° = 108°
or expressed in radians
3
=—- = = 7
arc 7 7 2n 10 2x 885 rad
Relatively small phase angles at not too high frequencies
can be measured more accurately in the X-Y mode with Lis-
sajous figures.
Measurement of an amplitude modulation
The momentary amplitude w at time t of a HF-carrier volt-
age, which is amplitude modulated without distortion by a
sinusoidal AF voltage, is in accordance with the equation
u =U, - sinQt + 0.5m - Uy: cos (2—a}t — 05m - U; - cos{Q+a}t
where U; = unmoduiated carrier amplitude
RQ =2xF = angular carrier frequency
@ =2nf = modulation angular frequency
m= = modulation factor (= 1 2 100%).
The lower side frequency F—fand the upper side frequency
F-+f arise because of the modulation apart from the carrier
frequency F. U;
0,5m-U;,
F-f F F+f
Amplitude and frequency spectrum for AM display (m = 50%)
Figure 1
The display of the amplitude-modulated HF oscillation can
be evaluated with the oscilloscope in the analog mode pro-
vided the frequency spectrum is inside the oscilloscope
bandwidth. The time base is set so that several wave of the
modulation frequency are visible. Strictly speaking, trigger-
ing should be external with modulation frequency (from the
AF generator or a demodulator). However, internal trigger-
ing is frequently possible with normal triggering (AT-
NORM. button depressed) using a suitable LEVEL setting
and possibly also using the time variable adjustment.
NCEE
NCCE
PIN VTL IN YT
PP Ee eye
EERE
YN YONG
PRES
Figure 2
Amplitude modulated oscillation: F = 1 MHz; f= 1 kHz;
m= 50 %; Uy = 28.3 MV ims.
a
Oscilloscope
setting
for
a
signal
according
to
figure
2:
Depress
no
buttons.
Y¥:
CH.
1;
20mV/em;
AC.
TIME/DIV.:
0.2ms/em.
Triggering: NORMAL with LEVEL-setting; internal (or
external) triggering.
If the two values a and bare read from the screen, the mod-
ulation factor is calculated from
a-b a-—b
——_ . = - 100 [%
a+b bzw. m atb [%]
where a = U, (1+m) and b = U, (1—m).
The variable controls for amplitude and time can be set
arbitrarily in the modulation factor measurement. Their
position does not influence the result.
Triggering and time base
A signal can be displayed only if the time base is running or
triggered. To produce a stationary display, triggering must
be synchronous with the test signal. This is possible by
using the test signal itself or by an externally supplied but
synchronous signal voltage.
The trigger voltage should have a certain minimum
amplitude. This value is called the trigger threshold. \t is
measured with a sine signal. When the trigger voltage is
taken internally from the test signal, the trigger threshold
can be stated as vertical display height in mm, through
which the time base generator starts, the display is stable,
and the trigger LED lights.
The internal trigger threshold of the HM 205 is given as
<5mm. When the trigger voltage is externally supplied, it
can be measured in V,, at the TRIG. INP. socket. Normally,
the trigger threshold may be exceeded up to a maximum
factor of 20.
The HM205 has two trigger modes, which are charac-
terized in the following.
Automatic Triggering
If the AT/NORM. pushbutton in the X field is in the out posi-
tion AT, the sweep generator is running without test signal
or external trigger voltage. A base line is always displayed
even without a signal applied. This trigger mode is therefore
called Automatic Triggering. Operation of the scope
needs, having a constantly visible trace, only a correct
amplitude and time base setting. A LEVEL adjustment is
neither necessary nor possible with automatic triggering.
This simple AT mode is recommended for all uncompli-
cated measuring tasks. However, automatic triggering is
also the appropriate operation mode for the “entry” into dif-
M12 205
Subject to change without notice

ficult measuring problems, e.g. when the test signal is un-
known relating to amplitude, frequency or shape. Presetting
of all parameters is now possible with automatic triggering;
the change to normal triggering can follow thereafter.
The automatic triggering works above 10Hz up to at least
20MHz. The changeover to the break down of the automa-
tic triggering at frequencies under 10Hz is abrupt. How-
ever, it can not be recognized by the TRIG. LED; this is still
blinking. Break down of triggering is best recognizable at
the left screen edge (the start of the trace in differing display
height).
The automatic triggering follows immediately all variations
or fluctuations of the test signal above 10Hz. However, if
the pulse duty factor of a square-wave signal changes so
much that one part of the square-wave reduces to a needle
pulse, switching over to normal triggering and using the
LEVEL controi can be necessary. With automatic triggering,
the trigger point lies approx. in the zero voltage crossing.
The time interval, required for the time base start, can be
too short at a steep zero crossing of the needle pulse. Then
normal triggering should be used.
Automatic triggering is practicable not only with internal but
also with external trigger voltage.
Normal Triggering
With normal triggering (AT/NORM. button depressed) and
LEVEL adjustment, the sweep can be started by signals
within the frequency range selected by the TRIG. coupling
switch. In the absence of an adequate trigger signal or
when the trigger controls (particularly the LEVEL con-
trol) are misadjusted, no trace is visible, i.e. the screen
blanked completely. ,
When using the internal normal triggering mode, it is possi-
ble to trigger at any amplitude point of a signal edge, even
with very complex signal shapes, by adjusting the LEVEL
control. Its adjusting range is directly dependent on the dis-
play height, which should be at least 5mm. If it is smaller
than 1cm, the LEVEL adjustment needs to be operated
with a sensitive touch. In the external normal triggering
mode, the same applies to approx. 0.6V external trigger
voltage amplitude.
Other measures for triggering of very complex signals are
the use of the time base variable control and HOLDOFF
time control, hereinafter mentioned.
Slope
The trigger point can be placed alternatively on a rising or fal-
ling edge of the test signal. This is valid with automatic and
with normal triggering. The selected slope is set with the
+/— button. The pius sign (button released) means an
edge, which is coming from a negative potential and rising
to a positive potential. That has nothing to do with zero or
ground potential and absolute voitage values. The positive
slope may alsolie in a negative part of a signal. A falling edge
(minus sign) triggers, when the +/— button is depressed.
However, with normal triggering, the trigger point may be
varied within certain limits on the chosen edge using the
LEVEL control.
Trigger coupling
The coupling mode and accordingly the frequency range of
the trigger signal can be changed using the TRIG. selector
switch. However, this is possible only with the TV SEP.
switch in OFF position.
AC: Trigger range = 10Hz to 20MHz.
This is the most frequently used trigger mode.
The trigger threshold is increasing below 10 Hz.
DC: Trigger range DC to 20MHz.
DC triggering is recommended, if the signal is to
be triggered with quite slow processes or if pulse
signals with constantly changing pulse duty fac-
tors have to be displayed.
Always work with normal triggering and
LEVEL adjustment.
Otherwise there is the possibility in the AT posi-
tion (automatic triggering) that the trigger point
may change or that triggering may not occur with
signals without zero crossing (e.g. with OC
offset). The balance of the corresponding channel
input should then be corrected (see “DC Balance
Adjustment”, page M8). Sometimes triggering is
easier with AC input coupling, because the sig-
nal then has its average value exactly at the oscil-
loscope’s ground potential.
HF: Trigger range 1.5kHzto40MHz (high-pass filter).
The HF position is suitable for all radio-frequency
signals. DC fluctuations and low-frequency
excess noise of the trigger voltage are suppres-
sed, giving a stable display. The trigger threshold
increases below 1.5kHz.
LF: Trigger range DC to 1kHz_ (low-pass filter).
The LF position is often more suited for low-fre-
quency signals than the DC position, because the
(white) noise in the trigger voltage is strongly sup-
pressed. So jitter or double-triggering of complex
signals is avoidable or at least reduced, in particu-
lar with very jow input voltages. The trigger
threshold increases above 1 kHz.
Subject to change without notice
M13 205

Line triggering
A part of a secondary winding voltage of the power trans-
former is used as mains/line frequency trigger signal (50 to
60 Hz) in the ~ position of the TRIG. selector switch. This
trigger mode is independent of amplitude and frequency of
the Y signal and is recommended for all mains/ine syn-
chronous signals. This also applies — within certain limits —
to whole number multiples or fractions of the line fre-
quency. Line triggering can also be useful to display signals
below the trigger threshold (less than 5mm). It is therefore
particularly suitable for measuring small ripple voltages of
mainsAine rectifiers or stray magnetic field in a circuit.
Magnetic leakage (e.g. from a power transformer) can be
investigated for direction and amplitude using a search or
pick-up coil. The coil should be wound on a small former
with a maximum of turns of a thin lacquered wire and con-
nected to a BNC connector (for scope input) via a shielded
cable. Between cable and BNC center conductor a resistor
of at least 100Q should be series-connected (RF decou-
pling). Often it is advisable to shield statically the surface of
the coil. However, no shorted turns are permissible.
Maximum, minimum, and direction to the magnetic source
are detectable at the measuring point by turning and shift-
ing the coil.
Triggering of video signals
The built-in active TV-Syne-Separator (separation of the
sync pulses from the video signal and following amplifica-
tion) even allows the display of noisy, changing in amplitude
or distorted video signals, alternatively triggered with line
(or horizontal) frequency or frame (or vertical) frequency.
The TV SEP. lever switch has three positions. The OFF
position serves to all normal operations; the TRIG. selector
switch is operative. The TV: H position (horizontal 4 line)
and the TV: V position (vertical & frame) are used for video
triggering. The TRIG. coupling switch is inoperable in these
both positions. In the TV: V position (frame triggering), a
low-pass filter or integrating network is connected into cir-
cuit, which forms a trigger pulse sequence with frame fre-
quency from the vertical sync pulse (incl. pre- and post-
equalizing pulses).
For accurate function of the sync separator, the slope of the
sync pulses should correctly be adjusted (corresponding to
the position of the sync pulses in the composite color sig-
nal. lf the sync pulses are placed above the picture content,
the +/— button should be released. The trigger point lies on
the rising front edge of the sync pulse. If they are below the
picture content, the +/— button should be depressed. The
trigger point lies on a falling (negative) front edge of the sync
pulse. This setting of the slope is valid for line and frame fre-
quency. An incorrectly set slope results in an unstable dis-
play. The trigger slope cannot be changed using the
INVERT buttons. The +/— button relates always to the
input signal! Video signals are triggered in the automatic
mode. Therefore the adjustment of the trigger point with
LEVEL knob is superfluous. The internal triggering is virtu-
ally independent of the dispiay height, which may differ
from 0.8 to 8cm. Depressing the AT/NORM. button results
in the difference (opposite to AT) that the screen is blanked
without trigger signal (turning the LEVEL knob is ineffectual).
Aside from the TV SEP. switch and the +/— button setting,
a time coefficient, adequate to the measuring purpose,
should be selected on the TIME/DIV. switch. The basic
positions for H (horizontal & line) and V (vertical & frame)
are marked on the scale of the TIME/DIV. switch. How-
ever, the TIME/DIV. knob may be turned more to the right
(without break down of the triggering), if more details in the
video signal should be required. More adventageous,
because one video field is suppressed, is the use of the 10-
fold expansion with the X-MAG. x10 button and the HOLD-
OFF time setting. Disconnecting the trigger circuit (e.g. by
rapidly pressing and releasing the EXT. button) can result in
triggering the consecutive (odd or even) field.
Setting: TV: V, 2ms/em, HOLDOFF knob at the right stop,
X-MAG. x10 button depressed, searching the picture detail
with X-POS. knob, additional X-expansion (x 2.5) with time
variable knob fully cw. So the International Insertion Test
Signals including Video Text and VPS etc. in the vertical
blanking interval are fully visible with a 25:1 expansion ratio.
The sync-separator-circuit also operates with external trig-
gering. It is important that the voltage range (0.3V,,, to 6V,,)
for external triggering should be noted. In addition, the cor-
rect slope setting is again critical, because the external trig-
ger signal may not have the same polarity or pulse edge as
the test signal. This can be checked, if the external trigger
voltage itself is displayed at first (with internal triggering).
Generally, the composite video signal has a high DC con-
tent. With a constant video information (e.g. test pattern or
color bar generator), the DC content can be suppressed
easily by AC input coupling of the oscilloscope
amplifier.With a changing picture content (e.g. normal pro-
gram), DC input coupling is recommended, because the dis-
play varies its height on screen with AC input coupling at
each change of the picture content. The DC content can be
compensated using the Y-POS. control so that the signal
display lies in the graticule area. Then the composite video
signal should not exceed a vertical height of 6cm.
External triggering
The internal triggering is disconnected by depressing the
EXT. button. The timebase can be triggered externally via
M14 205
Subject to change without notice

the TRIG. INP. socket using a 0.3V,, to 6V,,voltage, which
is in syncronism with the test signal. This trigger voltage
may have completely different form from the test signal
voltage. Triggering is even possible — in certain limits —
with whole number multiples or fractions of the test fre-
quency, but only in locked phase relation.
The input impedance of TRIG. INP. socket is approx.
0.8MQ 1130 pF. The maximum input voltage of the input cir-
cuit is 100V (DC + peak AC). Only 6V,, maximum are
required for a good external triggering.
Trigger indicator
An LED on condition (to the left of the TRIG. switch) indi-
cates that the sweep generator is triggered. This is valid
with automatic and with normal triggering. The indication of
trigger action facilitates a sensitive LEVEL adjustment, par-
ticularly at very low signal frequencies. The indication
pulses are of only 100ms duration.
Thus for fast signals the LED appears to glow continuously,
for low repetition rate signals, the LED flashes at the repet-
ition rate or — at a display of several signal periods — not
only at the start of the sweep at the left screen edge, but
also at each signal period.
Holdoff-time adjustment
If it is found that a trigger point cannot be iocated on
extremely complex signals even after repeated and careful
adjustment of the LEVEL control in the normal triggering
mode, a stable display may be obtained using the HOLD-
OFF control (in the X-field). This facility varies the hold-off
time between two sweep periods approx. up to the ratio
10:1. Pulses or other signal waveforms appearing during
this off period cannot trigger the timebase. Particularly with
burst signals or aperiodic pulse trains of the same
amplitude, the start of the sweep can be delayed until the
optimum or required moment.
A very noisy signal or a signal with a higher interfering
frequency is at times double displayed. It is possible
that LEVEL adjustment only controls the mutual phase
shift, but not the double display. The stable single dis-
play of the signal, required for the evaluation, is easily
obtainable by expanding the holdoff time. To this end
the HOLDOFF knob is slowly turned to the right, until
one signal is displayed.
A double display is possible with certain pulse signals,
where the pulses alternately show a small difference of the
peak amplitudes. Only a very exact LEVEL adjustment
makes a single display possible. The use of the HOLD-OFF
knob simplifies the right adjustment.
After specific use the HOLD-OFF control should be re-set
into its calibration detent, otherwise the brightness of the
display is reduced drastically. The function is shown in the
following figures.
Function of var. HOLD-OFF control
heavy parts are displayed
are |
Fig. 2 adjusting the
| HOLD-OFF time
|
Fig. 1 shows a case where the HOLD-OFF knob is in the minimum position
and various different waveforms are overlapped on the screen, making the
signal observation unsuccessful.
Fig. 2 shows acase where only the desired parts of the signal are stably dis-
played.
Component Tester
General
The HM 205 has a built-in electronic Component Tester (ab-
breviated CT), which is used for instant display of a test pat-
tern to indicate whether or not components are faulty. The
CT can be used for quick checks of semiconductors (e.g.
diodes and transistors), resistors, capacitors, and inductors.
Certain tests can also be made to integrated circuits. All
these components can be tested in and out of circuit.
The test principle is fascinatingly simple. The power trans-
former of the oscilloscope delivers a sine voltage, which is
applied across the component under test and a built-in fixed
resistor. The sine voltage across the test object is used for
the horizontal deflection, and the voltage drop across the
resistor (i.e. current through test object) is used for vertical
deflection of the oscilloscope. The test pattern shows a cur-
rent-voltage characteristic of the test object.
Since this circuit operates with mains/ine frequency (50 or
60 Hz) and a voltage of 8.5V max. (open circuit), the indicat-
ing range of the CTis limited. The impedance of the compo-
nent under test is limited to a range from 20Q to 4.7kQ.
Below and above these values, the test pattern shows only
short-circuit or open-circuit. For the interpretation of the dis-
played test pattern, these limits should always be borne in
mind. However, most electronic components can normally
be tested without any restriction.
Subject to change without notice
M15 205

seer
LS
Using the Component Tester
The CT is switched on by depressing the CT pushbutton
beneath the screen. This makes the vertical preamplifier
and the timebase generator inoperative. A shortened hori-
zontal trace will be observed. It is not necessary to discon-
nect scope input cables unless in-circuit measurements are
to be carried out. In the CT mode, the only controls which
can be operated are INTENS., FOCUS, and X-POS.. All
other controls and settings have no influence on the test
operation.
For the component connection, two simple test leads with
4mm @ banana plugs, and with test prod, alligator clip or
sprung hook, are required. The test leads are connected to
the insulated CT socket and the adjacent ground socket in
the Y-Section. The component can be connected to the test
leads either way round.
After use, to return the oscilloscope to normal operation,
release the CT pushbutton.
Test Procedure
Caution! Do not test any component in live circuitry —
remove all grounds, power and signals connected to
the component under test. Set up Component Tester as
stated above. Connect test leads across component to
be tested. Observe oscilloscope display.
Only discharged capacitors should be tested!
A built-in quick-acting fuse protects the CT and the oscillo-
scope against mis-operation, e.g. device under test not dis-
connected from mains/line supply. In that case the fuse will
blow. For fuse replacement the oscilloscope has to be
opened (see service instruction page S1 “Instrument Case
Removal"). The fuse is located on the bottom side of the
instrument (close to the CT pushbutton). Make sure that
only fuses of the specified type are used for replacement:
5x20mm, quick-acting, 250V, C,50mA (IEC 127/ll or DIN
41661).
Test Pattern Displays
Page M18 shows typical test patterns displayed by the var-
ious Components under test.
— Open circuit is indicated by a straight horizontal line.
— Short circuit is shown by a straight vertical line.
Testing Resistors
If the test object has a linear ohmic resistance, both deflect-
ing voltages are in the same phase. The test pattern
expected from a resistor is therefore a sloping straight line.
The angle of slope is determined by the resistance of the
resistor under test. With high values of resistance, the
slope will tend towards the horizontal axis, and with low val-
ues, the slope will move towards the vertical axis.
Values of resistance from 20Q to 4.7kQ can be approxi
mately evaluated. The determination of actual values will
come with experience, or by direct comparison with a com-
ponent of a known value.
Testing Capacitors and inductors
Capacitors and inductors cause a phase difference
between current and voltage, and therefore between the X
and Y deflection, giving an ellipse-shaped display. The posi-
tion and opening width of the ellipse will vary according to
the impedance value (at 50 or 60Hz) of the component
under test.
A horizontal ellipse indicates a high impedance or a
relatively small capacitance or a relatively high induct-
ance.
A vertical ellipse indicates a small impedance or a reia-
tively large capacitance or a relatively small induct-
ance.
A sloping ellipse means that the component has a con-
siderable ohmic resistance in addition to its reactance.
The values of capacitance of normal or electrolytic
capacitors from 0.74F to 1000uF can be displayed and
approximate values obtained. More precise measurement
can be obtained in a smaller range by comparing the
capacitor under test with a capacitor of known value. Induc-
tive components (coils, transformers) can also be tested.
The determination of the value of inductance needs some
experience, because inductors have usually a higher ohmic
series resistance. However, the impedance value (at 50 or
60 Hz) of an inductor in the range from 20 to 4.7k@ can
easily be obtained or compared.
Testing Semiconductors
Most semiconductor devices, such as diodes, Z-diodes,
transistors, FETs can be tested. The test pattern displays
vary according to the component type as shown in the
figures below.
The main characteristic displayed during semiconductor
testing is the voltage dependent knee caused by the junc-
tion changing from the conducting state to the non conduct-
ing state. It should be noted that both the forward and the
reverse characteristic are displayed simultaneously. This is
a two-terminal test, therefore testing of transistor amplifica-
tion is not possible, but testing of a single junction is easily
and quickly possible. Since the CT test voltage applied is
only very low (max. 8.5V,ms), all sections of most semicon-
ductors can be tested without damage. However, checking
the breakdown or reverse voltage of high voitage semicon-
ductors is not possible. More important is testing compo-
nents for open or short-circuit, which from experience is
most frequently needed.
ea
x
SS
Sus
SS
SGA
M16 205
Subject to change without notice