Sinclair DM350 User manual

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DIGITAL MULTIMETERS DM350 and DM450
INSTRUCTION MANUAL

INDEX
Power
Function and Range Selection
Overrange Indication
Input Terminal Polarity
Disposable Batteries
Rechargeable Batteries
Low Battery Indication
Zero
Overload and Protection
Safety Precautions
Making Complex Waveform AC Measurements
Avoiding Ground Loop Interference
Using the Resistance Ranges
Testing of Semi—Conductor Junctions
Technical Specifications
Calibration
Maintenance
Guarantee
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8, 9,10
10
10
12
INTRODUCTION
The Sinclair DM350 and DM450 are laboratory quality, digital
multimeters differing only in their accuracy and resolution (scale
length).
Both instruments are battery-operated and housed in arobust,
slim—style case, making them suitable for portable applications as
well as bench work. The large LED display has an exceptionally
wide viewing angle and has avariable brightness control.
Both instruments are full multimeters measuring AC~ and DC
:volts, AC~ and DC:: current, Resistance and diode volts, in
atotal of 34 ranges.
Special features include ultra wide current handling from 1nA up
to 10 amps, and very high input impedance on the 2000mV range
(in excess of 1000M Q).
The DM350 and DM450 will operate from low cost disposable
cells or from an optional AC adaptor. This adaptor also serves as a
charger when the optional rechargeable battery pack is fitted.
ACCESSORIES
The following optional accessories are available for the DM350
and DM450 multimeters:
AC adaptor/chargers for 117V, 220V and 240V
Eveready carrying case with lead stowage compartment
Rechargeable battery units
Deluxe test lead kit
30KV High voltage DC probe
Service manual

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OPERATION
Power
The instrument is switched on by depressing the power on-off
button (1). If operation from AC line power is required, an
approved AC adaptor (see Note 1on page 4) may be plugged into
the power jack at the rear of the instrument (2). Connecting the
AC adaptor automatically increases the display brightness to
maximum.
The instrument may be operated from disposable cells (see Note 2
on page 4) or from the optional rechargeable battery pack.
Batteries should be fitted into the holder housed under the slide-
off cover (3), care being taken to observe polarity. It is essential
that the disposable/rechargeable selector switch (4) is positioned
correctly before connecting the AC adaptor/charger.
Function and Range Selection
The Function and Range are selected by the push-buttons (5) and
(6)--
DC :. volts: 6ranges are available covering voltages up to
1200 volts. The input is applied between
terminals (8) and (7). The 2000mV ultra high
impedance range is selected by simultaneous
depression of the Vand mA buttons and a
release of all the range buttons (half depression
allows release). DM450 will read in 21—2),
AC~ volts: 5ranges are available for inputs up to 750 volts
rms connected to terminals (8) and (7). The
instrument senses the mean value of the input
signal and is calibrated to read the rms value of
asine wave. A DC level on the AC signal will
not affect the accuracy of the AC reading pro-
vided that DC level plus AC rms level does not
exceed the maximum reading of the range.
DM450 displays only 3% digits on 200mV.
DC: Current: 8ranges are available for inputs up to 10A
continuous (20A intermittent). Connect to
terminals (8) and (7) except 10A which is to
(9) and (7). 20pA and 29A ranges are available
by depressing Vand mA function buttons
simultaneously —this gives a[LA/10 function
which can be used with the 200 or 20 range
buttons.
AC~ Current: As for DC current. Sensing information as for
AC volts. DM450 displays only 3‘7digits.
Resistance: 6ranges are available for resistances up to
20M 9. Connect between terminals (8) and
(7)-
Diode Test: Select 2K9. Connect diode across terminals
(8) and (7) with anode to common (7).
Forward voltage drop is displayed in volts.
Overrangelndication
DM350: When areading of 1999 is exceeded, overrange is in-
dicated by blanking of all but the most significant digit
which is displayed as a1with anegative sign if
appropriate.
DM450: When areading of 19999 is exceeded, overrange is
indicated by areading of $0000 and flashing of the
whole display.
When overrange indication occurs, the next highest
range should be selected.
Input Terminal Polarity
The negative (common) terminal (7) is the low potential terminal
with respect to ground. If the positive terminal is taken negative
with respect to the common terminal, anegative sign will be
automatically displayed. When measuring AC~ signals, or
DC..—. signals with AC~ superimposed on' them, the common
terminal should be connected to the ground side of the signal
being measured regardless of the actual polarity.

Power
Note1 For safety reasons, only an approved adaptor may be
used; use of any other will void the guarantee. In some
countries, the correct Sinclair adaptor may not be
available in which case, the dealer will supply an
alternative approved unit.
Note 2 For disposable cell operation, 4off Csize cells should
be used. If possible, high power or Alkaline batteries
should be used. Alist of suitable types is given below
—ask your dealer if in doubt. To obtain long battery
life, the display brightness control (10) should be set
to the minimum acceptable level and the meter switched
off whenever measurements are not being made.
In the 'disposable' position, inserting the power jack
will automatically disconnect the internal batteries. In
the 'rechargeable' position, inserting the powerjack will
cause the internal batteries to be charged. This charging
will take place at constant rate whether the instrument
is switched 'on' or 'off’.
Disposable Batteries
Suitable cells for use in the DM35O and DM450 are as follows:
Size Classification: ASA IEC Japan
CR14 AM2
Normal Types: SP11, 835, 120, V8735, 114, 110LP,
214, U11 MJ
High Power Types: HP11, 935, 814, V5035A, M14-F, 111,
IC, 27
Alkaline Types: Mn 1400, E93, AL-1, VS1335
Rechargeable Batteries
Special Sinclair rechargeable units are available. Full instructions
for use are provided in the pack.
Low Battery Indication
Indication of failing batteries is provided by flashing of the
display. This occurs when the voltage falls below 4.4 volts, and
gives some time to continue making measurements before reading
errors will occur.
Rechargeable batteries should not be allowed to fully discharge.
Weak or dead disposable cells should never be left in the instru-
ment since they may leak damaging chemicals.
Zero
Both instruments have automatic adjustment of zero. Zero offset
can, however, occur as follows:
DC: Leakage currents of up to -. ZOOpA can cause
offsets on the 200mV and 2V ranges which will
disappear when alow impedance source is con-
nected. On the DM450 azero reading of up to ,l_
0.02% of range may appear on 200mV, 20V, and all
DC current ranges. This is allowed for in the speci-
fication but can be subtracted from the reading to
obtain amore accurate result.
On 2000mV ultra high impedance, azero will not be
obtained until the input is connected to an external
impedance.
AC: Zero reading should be disregarded until asource is
connected. Zero reading of up to 10.1% of range
may occur on the 20 volt and 200mV ranges. This
should not be subtracted from the reading.
Resistance: On the 2009 range, shorting out the leads will
produce anon zero reading, which should be
subtracted from the measurement reading.

Overload and Protection
All ranges with the exception of the 2000 range on AC and DC
volts and the 20A range on AC and DC current, can be used up to
the full scale display reading.
Voltage ranges have inherent protection. Resistance ranges have
high voltage electronic protection. Current ranges are protected
by afuse mounted at the rear (11). This fuse should be a2A fast
blow ceramic or plastic body fuse —use of aslow-blow type will
void the guarantee.
No protection is incorporated on the 10A range. This range can be
used up to 20A for periods not exceeding 10 seconds.
The meter is fully protected against damage from accidental
connection of high voltages such as AC line across sockets (7)
and (8). The following rules should however be observed.
(a) Never connect an input of greater than the maximum
permissable overload for the range.
(b) Always select the correct function and range before
connecting the input.
(c) Never connect the meter to avoltage source when the
current function is selected.
(d) Take extra care when connecting to the 10A socket'(9)
since it is unprotected.
Note
The standard leads and prods supplied with the meter are not
suitable for currents in excess of 5amps.
Safety Precautions
The DM350 and DM450 have been designed to the highest
safety standards but safe operation depends on the user, so we
recommend the following rules.
1. Never connect avoltage to the instrument which causes the
common terminal to be raised more than 750 volts above
ground.
2. Never use anything but an approved AC adaptor to power the
instrument.
3. Use extreme caution when working with voltages above 50V.
Always disconnect power from the circuit being tested whilst
connecting or disconnecting test leads.
If the common terminal is at ahigh voltage with respect to
ground, the 10A socket will be at the same high voltage.
4. Never unplug atest lead from the instrument while it is still
connected to ahigh voltage.
5. Use extreme caution when working with AC-DC equipment
withlive or'hot’ chassis.

Making Complex Waveform AC Measurements
The Sinclair DM350 and DM450 are calibrated to display the rms
value of asine wave whose average half-wave rectified value is
actually measured. Thus, if the input waveform is not sinusoidal,
the displayed value will not be the rms but will be in error by an
amount dependent on the waveform shape. Although the rms
value gives the heating power of the waveform, this is often less
valuable to know than the peak waveform height. The table below
shows how to obtain both from the reading displayed.
Avoiding Ground Loop Interference
if the AC adaptor/charger is connected, ground loop currents can
be set up if the signal source ground is at adifferent potential than
AC power ground. This effect will be greatly attenuated by the
meter, but to avoid it completely, revert to battery operation. When
making AC measurements, AC potential differences can also
inject signals by capacitive coupling through the adaptor. Again
revert to battery operation if this becomes aproblem.
Multiply Displayed
Wave- Displayed True rms Value by
form Value Value for rms for peak
sine 0.707E 0.707E 1.0 1.414
square 1.11 E1.015 0.9 0.9
triangle 0.555E 0.547E 1.034 1.801

Using the Resistance Ranges
With the exception of the 200 Qrange, the resistance ranges are
‘high power', ie they generate voltage across the resistor at
—20mV per 1% of full scale reading. If the resistor is in place
across asemiconductor junction, this junction could forward bias
and cause an error if the reading is above 10% of range. To avoid
this, either select the next range, or reverse the leads.
(On the 20M 9range instability of reading may result from noise
pick-up across the high impedance. To avoid this, use short leads,
or twist leads together).
Testing of Semiconductor Junctions
The 2K9 resistance range acts effectively as a1mA constant current
source with the common socket as positive terminal. By connect-
ing asemiconductor junction such that it is forward biased, the
meter will read the approximate forward voltage drop in volts.
When the junction is connected in reversed bias mode,the current
source will saturate to its maximum open circuit voltage, and the
meter will read overrange. Afurther indication of the condition of
the junction can be obtained by selecting higher resistance
ranges until areading is obtained. The appropriate low voltage
reverse leakage current can then be determined by referring to the
excitation current for the range quoted in the specification on
page 9.

(19°C—24°C)
SPECIFICATION
DC: VOLTAGE r:of reading fs :of full scale
l
Max.
DM450 DM350 Permissable Input
lRange Accuracy Resolution Accuracy Resolution Overload Impedance
200mV 0.05%ri0.02%fs 10ml 0.1%r i0.1%fs 1UOILI/ 4OOVpk 10M 9
2000mV 0.05%rf0.01%fs 100ILV 0.1 %r 10.05%fs 1mV 400Vpk >1000M 9
2V 0.05%ri~0.01%fs 100uV 0.1%r :l;0.05%fs 1mV 400Vpk 10M Q
20V 0.1%r :0.01%fs 1mV 0.25%ri-_0.05%fs 10mV 1200Vpk 10M (2
200V 0.1%r ;f0.01%fs 10mV 0.25%r:t0.05%fs 100mV 1200Vpk 10M Q
1200V 0.1%r 330.01%fs 100mV 0.25%rj:0.05%fs 1V1200Vpk 10M 9
AC~ VOLTAGE 50/60Hz
Frequency Response within
112% additional error
200mV 0.2%r 10.1 %fs 1OOyLV 0.25%ri0.2%fs 100[J.V 250V rms 10M Q20Hz —ZOkHZ
2V 0.2%r +0.02%fs 100ng O.25%ri0.1%fs 1mV 250V rms 10M Q20Hz —20kHz
20V 0.25%r10.1%fs 1mV 0.4%r :O.2%fs 10mV 750V rms 10M Q20Hz —20kHz
200V 0.25%ri0.02%fs 10mV 0.4%r 31:0.1 %fs 100mV 750V rms 10M Q20Hz —20kHz
750V O.25%r:1:0.02%fs 100mV 0.4%r i0.1%fs 1V 750V rms 10M Q20Hz —500Hz 5x106VHz max.
DC: CURRENT
Max.
Voltage
Burden
ZuA 0.15%r;0.1%fs 0.1nA 0.2%r:0.1%fs 1nA 2A 2V
20 {LA 0.15%rt0.02%fs 1nA O.2%r,+_0.1%fs 10nA 2A 2V
200 ILA 0.15%ri0.02%fs 10nA 0.2%ri0.1%fs 100nA 2A 200mV
2mA 0.15%r_i:0.02%fs 100nA 0.2%r_1—0.1%fs 1IA 2A 200mV
20mA 0.5%r :t0.02%fs 1{LA 0.5%r,t0.1%fs 109A 2A 200mV
200mA 0.5%r i0.02%fs 1011A 0.5%r;‘~_0.1%fs 100 5LA 2A 200mV
2000mA 0.5%r :k0.02%fs 100nA 0.5%r,£0.1%fs 1mA 2A 300mV
10A 2.0%r i0.1%fs 1mA 2.0%ri0.1%fs 10mA 10A 1V
(20A 10 secs)

AC~ CURRENT 50/60Hz
meaxée Freq1u1e;cy rasponse within
5oaddltlonal error
Burden
211A 0.3%r i0.2%fs 1nA 0.35%ri0.2%fs 1nA 2A 2V 20Hz —10kHz
200A 0.3%r i0.15%fs 10nA 0.35%r:j:0.15%fs 10nA 2A 2V 20Hz —10kHz
200pLA 0.3%r ;t0.15%fs 100nA 0.35%rj 0.15%fs 100nA 2A 200mV 20Hz —- 10kHz
2mA 0.3%r ;0.15%fs 1pLA 0.35%r:,0.15%fs 1{LA 2A 200mV 20Hz —10kHz
20mA 0.65%rfi0.15%fs 10(LA 0.65%r;4:0.15%fs 10ng 2A 200mV 20Hz —10k Hz
200mA 0.65%r:70.15%fs 1OOpLA 0.65%r:0.15%fs 100 HA 2A 200mV 20Hz —10kHz
2000mA O.65%r:l:0.15%fs 1mA 0.65%ri0.15%fs 1mA 2A 300mV 20Hz —10kHz
10A 2.5%r i0.15%fs 10mA 2.5%r i0.15%fs 10mA 10A 1V 20Hz —1kHz
(20A 10 secs)
RESISTANCE
Excitation
Current
Approx. Max. o/c Voltage
200 Q0.1%r:‘0.1%fs 1Om Q0.2%ri0.1%fs 100m 9400Vpk 1.5mA 4V
2K (2 0.1%ri0.02%fs 100m 00.2%ri0.05%fs 1Q400Vpk 1mA 4V
20K 90.1%r_—':0.02%fs 1Q0.2%ri0.05%fs 1O (2 400Vpk 100 ”A 4V
200K QO.1%r;~0.02%fs 10 QO.2%ri0.05%fs 100 Q400Vpk 101LA 4V
2000K Q0.1%r;‘~_0.02%fs 100 Q0.2%ri0.05%fs 1K9400Vpk 1”A 4V
20M 91.0%ri0.1%fs 1K 91.0%riO.1%fs 10K (2 400Vpk 0.1pLA 4V
DIODE
TEST 400Vpk 1mA 4V
Accuracy specification at calibration maintained typically for 6months.