Keithley 3910 User manual

Operator's Manual
Model 3910
Function Synthesizer
01991, Keithley Instruments,Inc.
All Rights Resewed
Instruments Division
Cleveland, Ohio, U. S. A.
-)ocument Number: 3910-900-01

All Keithley product names are trademarksor registered hademarksof Keithley Instruments, Inc.
Other brand and product names are trademarksor registeredtrademarks of their respectiveholders.

Safety Precautions
Thefollowingsafetyprecautionsshouldbeobservedbefore using theModel3910FunctionSynthesizer and anyassoci-
ated instruments.
This instrument is intendedforuse by qualified personnelwhorecognizeshockhazardsand are familiar with the safety
precautionsrequired toavoid possible injury. Read over this manual carefullybefore using theinstrument.
Exerciseextremecautionwhen
a shock hazard is presentatthe test circuit. TheAmericanNational StandardsInstitute
(ANSI) statesthat a shock hazard existswhen voltagelevelsgreater than 30V rms or 42.4V peak arepresent. A good
safetypractice is to expect that hazardous voltage ispresent in any unknown circuit before measuring.
Inspect the connectingcablesand testleadsforpossiblewear, cracks, orbreaksbeforeeachuse.
For maximum safety, donot touch the test cablesor any instrumentswhile power
is applied to the circuitunder test.
Turn off the power and dischargeanycapacitors before connectingordisconnectingcables from theinstnunent.
Donot touch
any objectwhich couldprovide a currentpath to the commonsideof thecircuitunder test or power line
(earth) ground.Alwaysmakemeasurements with dry handswhilestandingon a dry, insulatedsurfacecapableof with-
standing the voltagebeing measured.
Instrumentationand accessoriesshouldnot beconnected to humans.

Table of Contents
SECTION 1 - General Information
INTRODUrnON... ........................................................... 1-1
FEA- ................................................................... 1-1
WARRANTYINFORMATION
.................................................... 1-2
MANUALADDENDA .......................................................... 1-2
SAFETYTERMSANDSYMBOLS.................................................. 1-2
UNPACKINGANDREPACKING ................................................. 1-2
Unpacking
........................................................ 1-2
Shipmentcontents ........................................................... 1-2
Operator's Manual .. .. .. .. . ..... . ... . . . . ... .... .... . ... .. ,, . . . .... ... . . . . .. . . 1-2
RepackingForShipment
............................ . .......................... 1-2
OPTIONALACCESSORIES
...................................................... 1-3
SPECIFICATIONS ....................,..................................... 1-3
SECTION 2 - Getting Started
INTRODUCTION .............................................................. 2-1
INSTALLATION ........................,,.................*............. 2-1
InstalIationLocation ....................c..................................... 2-1
Cooling
...........................................................,........ 2-1
LINEPOWERSUPPLY
.......................................................... 2-2
LINE Voltage Selector Switch .. . . ... . . .. .... . .. . .. . .. .. .. ..... .... . . .. .. ....... .
2-2
LineReceptadeConnection
..................................................... 2-2
LineFuse .................................................................. 2-2
HANDLINGPRECAUTIONS
.. .... . .... ...... . . .. .. ...... . . . .. .. ... . . . ..... .... ..
2-2
BASICOPERATlON ............................................................ 2-3
FrontPanelSummary
......................................................... 2-3
TypicalTestConnections
...................................................... 2-3
OperatingExamples
..................................................... 2-4
SECTION 3 - Operation
INTRODUCTION .............................................................. 3-1
FRONTPANEL
AND REAR PANEL DESCRIPTION ... .... . . . ... .... ... . . .... . . ... . . . .
3-1
FrontPanelDescription
........................................................ 3-1
RearPanelDescription
........................................................ 34
INPUT AND OUTPUTCONNECTIONS . ...... ... . . .... .. .. . .... .... . . . ... ... . . . ...
33
Inputconnection
....................,.......,,,......................... 3-5
OutputConnections
.......................................................... 3-5
STARTUP .................................................................... 345
OPERATINGPROCEDURES . ...... . . .... .... . .. . .... . . . . .... .... . . .... . . . . .... ..
3-7
Errorcodes ................................................................ 3-7

3.5.2 FrequencySetting ............................................................ 3-7
3.5.3 OutputAmplitude ........................................................... 3-8
3.5.4 DCOffset .................................................................. 3-8
3.5.5 WaveformSelection, Square-Wave
Duty Cycle, and Synchronous Output .................. 3-8
3.5.6 OsdationMode ............................................................. 3-9
3.5.7 TriggerParameters ......................................................... 3-11
SECTION 4 - GPIB Interface
INTRODUmON .............................................................. 41
GPIBOverview .............................................................. 4-1
MajorGPIBSpecifications ...................................................... 41
BusLineSignAandOperation
.................................................. 41
GPIBHandshaking ........................................................... 42
........................................................ Data Transfer Example 43
BasicTalkerFunctions..... .................................................... 43
BasicListenerFunctions
....................................................... 4-3
BasicControUerFunctions ...................................................... 4-3
MuIti-line InterfaceMessages ................................................... 43
OVERVIEW OF MODEL 3910 GPlB INTERFACE ...................................... 4-6
Introduction .............................................................. 4-6
Specifications .............................................................. 4-45
MODEL 3910 PROGRAM CODES ..................................................
4-9
TYPICALEXECUTZON TIMES.................................................... 412
SAMPLEPROGRAMS
.......................................................... 4-13

List of Illustrations
SECTION 2 - Getting Started
......................................................
Figure2-1 Front Panel Summary 2-3
.......................................................
Figure 2-2 Typical Connections 2-4
SECTION 3 - Operation
Figure3-1
Figure3-2
Figure
3-3
Figure 3-4
Figure 3-5
Figure 34
Figure 3-7
Figure 3-8
Model3910FrontPanel ..................................................... 3-2
Mode13910RearPanel ..................................................... 3-4
LogicInputCircuit ........................................................ 3-5
OutputCircuit ........................................................... 3-6
...................
PhaseRelationshipbetween FCTN OUT Waveform and SYNC OUT 3-9
....................
RelationshipbetweenTrigger Signal andOscillation in TRIG Mode 3-10
RelationshipbetweenTrigger
Signal andOscillation in GATE Mode ................... 3-11
..........................................
Definitionof Phaseof each Waveform
3-12
SECTION 4 - GPXB Interface
.......................................................
Figure 41 InterfaceConnector 4-2
.................................................
Figure42 Handshake Timing Diagram 4-3
.....................................................
Figure 4-3 Data Transfer Example 4-4
Figure44 RogramCodeSyntax...................................................... 4-8

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List of Tables
SECTION 2 - Getting Started
Table2-1 FuseReplacement ......................................................... 2-2
SECTION 4 - GPIB Interface
Table41 Multiple-lineInterfaceMessage .............................................. 4-5
Table 42 InterfaceFunctions ........................................................ 4-6
Table 43 BusDriverSpecifications ................................................... 4-6
Table 4-4 Response to InterfaceMessages ............................................... 47
Table 45 StatusByte .............................................................. 49
Table 44 Mode13910Main ParameterSettingMessages .................................... 410
Table
47 TypicalExemtionTmes .................................................... 4-12

SECTION 1
General Information
The Model3910 Function Synthesizer can generate fre-
quenciesbetween O.lmHz and IMHz. The Model 3910
can generatethe entire band at a resolution of O.lmHz,
with ahigh-frequency accuracyof SOppm.
~ive~~waveforms,sine
%, hiangle%, squaren, ris-
ingsawtooth A, and fallingsawtood are available. A
maximum offlOV DC can be added onto each output.
Maximumoutput voltageforallwaveforms
is 20V p-p/
no load or10Vp-p/SOQ load.
Since frequencies
are synthesized directly by a custom
LSI digital IC, accuracyandstabilityare high, andthe fre-
quencyswitchingtimeisshort.Anotheradvantage is the
continuity of phase atfrequencyswitchover.
In addition to continuous oscillation, burst oscillation,
triggeroscillation,andgateoscillationareavailable. The
Model 3910 alsoprovidesa continuous
output of direct
currentvoltage.
An externaltriggerinputprovides an ex-
ternaltriggersignal
during triggerorgateoscillation. The
square-wavedutycycle is alsovariable.
TheModel3910
uses a singleline, 11 -character LED dis-
play to display the
values of oscillation frequency, pa-
rameters, and othervalues. Settingsareeasily made
us-
ing push-buttonkeysand rotary knobs.
A GPIl3 (IEEE488) interface is available as anoptionfor
the Model 3910. With theexceptionof the Am, arn-
plitudesetting; DC OFFSET, addedquantitysetting;and
DUTY VAR, duty ratio setting; a GPIB equippedModel
3910canbe programmed overthebusforthe
same oper-
atingmodes
and parametersthatcan be controlIed from
thefrontpanel.
1.2 FEATURES
Wide bandwidth: O.lmHz to lMHz (resolution
0.lmHz).
M0 ppm frequencyaccuracy.
Phasecontinuityatfrequencyswitchover.
Five
AC waveformsavailable: %,%,L , A, and\
Theduty cyclecan be set to valuesbetween 10%and
90% for frequenciesupto 100kH.z.
High output:20Vp-p/no load, f OVp-p/SOSUoad.
Low distortion:
0.3% or less (loHzto 100kHz).
DC output voltages available: klOV/no load,
fiV/50Qload.
Burst oscillation mode: Repeats oscillation of wave
number specified by mark wave(1-16) and spacewave
number
(1-16).
Triggeroscillationand gate oscillation:
Triggersource:
External by frontpanel BNC plugor
push-button key.

SECTION 1
General information
Start/stop phase: -360' to+360°.
Inputvoltage:
lTL level(pubup 74HC14 inputby
5.1K).
Minimum pulsewidth200nsec.
Trigger: Oscillateswavenumberspecifiedby wave
number (1-14)
by trigger signal.
Gate: Integral wave number oscillation by trigger
signal.
Waveform andfrequencyrange:
Sine wave, square wave (duty fixed);
O.lmEIz to
IMHz.
Trianglewave, squarewave (duty variable),rising
sawtooth wave, falling sawtooth wave;
O.l& to
IOOlcHz, oscillation possibleupto 1MHz.
Each parameter setting can be modified using the
MODIFY knobandtheCURSOR keys. The single line,
11 character LED display, clearly displays all neces-
saryinformation;oscilIation frequency,
GPIB address
(when installed),start/stop phase, mark wave num-
ber, and spacewavenumber.
Batterybacked-upmemorystorestheconfiguration
in
effectwhen power is turned off.
r Optional GPB interface allows the Model 3910 to be
programmed overtheGPIB (IEEE-488 interface bus).
The WARNING heading used in this manual explains
dangers that mightresult in personal injj ordeath. Al-
waysread the associated information very carefullybe-
foreperformingthe indicatedprocedure.
The CAUTION heading used in this manual explains
hazardsthatcoulddamagetheinshument.
Such damage
may invalidatethewarranty.
1.6 UNPACKINGAND REPACKING
1.6.1 Unpacking
After carefullyunpacking the instrumentfrom itsship-
pingcarton, inspectit for
any obvious signs of physical
damage. Report anysuch damage to theshippingagent
immediately.Savethe
original packingcartonforstorage
orpossible
future shipment.
1.6.2 Shipment Contents
1.3 WARRANTY INFORMATION
Warrantyinformation is locatedontheinsidefrontcover
of
this operatofs manual. Should your Model 3910 re-
quite
warranty service,contact the Keithley representa-
tive orauthorizedrepairfacility
in your area for further
information. When returning the instrumentfor repair,
besureto
fill out and indudetheserviceformattheback
of
this manualinordertoprovidetherepairfacility with
thenecessaryinformation.
1.4 MANUALADDENDA
Any improvementorchangesconcerningtheinshument
or manual
will be explained in an addendum included
with theunit. Be suretonote thesechangesandincorpo-
ratethem intothe manualbefore
using the unit.
1.5 SAFETY TERMS AND SYMBOLS
Thefollowingsafetyterms and symbolsarefound on the
instrumentorused in this manuaI.
A
The
symbol on the instrument indicates that the
user shouldrefer to the operatinginshctions.
ThefollowingitemsareincludedwitheveryModel
3910
order:
Model 3910 FunctionSynthesizer
Mode13910 Operator's Manual
Powercord
Fuse (IA,250V,
5.2 x 20mrn)
BNC to BNC signalcable
Additionalaccessories
as ordered.
1.6.3 Operator's Manual
If an additionalmanual is required, order the manual
package,Keithley
part number3910-900-00. The manual
padcage indudes
an operatois manual and any perti-
nentaddenda.
1.6.4 Repacking For Shfpment
Should it becomenecessarytoreturn theModel3910 for
repair, carefullypack theunitin
its originalpacking car-
tonortheequivalent. If theoriginalcarton is notavailable
ordamaged,
be sureto use acardboardbox of sufficient
strengthand room. Pad the emptyspaces in the carton
with adequatepackingmaterialtoholdthe unit firmly in
place.

Include thefollowinginformation:
Advise to the warranty status of theinstrument.
a Write ATENTION REPAIR DEPARl'MFNT on the
shippinglabel.
Fill outandincludethesenriceformlocatedatthe back
of this manual.
1.7 OPTIONAL ACCESSORIES
The followingaccessoriesare availablefor use with the
Model3910.
Models 3900-1 and
3900-2 Rack Mounting Kits: The
Model 3900-1 mounts one Model 3910
in a standard
19-inch rackTheModel3900-2 mounts twoModel3910s
sideby side
in a standard 19-inchrack Both kits include
all necessary hardwarefor proper rack mounting of the
instruments.
Model 7007 Shielded
IEEE-488 Cables: The Model
7007-1 (lm,
3.3R) and Model 7007-2 (2m, 6.6ft.) can be
used tointerfacetheModel3910 tothe IEEE-488 bus.
Model3911 IEEE-488 Interface:With theMode13911op-
tion a maximum of 15Model3910s can be connectedon
the samebus, data line transfer uses
a 3-linehandshake
method, enabling reliable data transfer between data
sending (talkers)and receivers (listeners)having differ-
ing datatransfer rates.
SECTION 1
General InJonnution
Model 7051-2 BNC-to-BNC Cable:TheModel7051-2 is
50Q BNC to BNC cable (RG68C) 2ft. (0.61111 in length.
TheModel7051-2 isterminatedwith maleBNC connec-
torsonboth ends.
Model
7051-5 BNC-to-BNC Cable: TheModel7051-5 is
50Q BNC to BNC cable (RG-58C) 5ft. (1.h) in length.
TheModel7051-5
is terminatedwith male BNC connec-
torsonboth ends.
Model
7051-10 BNC-to-BNC Cable:TheModel7051-10
is similartotheModels 7051 -2 and7051-5 exceptthatit is
loft. (2.4m) in length.
Model
77543 BNC-to-Alligator Cable: The Model
77543 is a 3ft.
(0.9m) 50Q cable (RG58C), terminated
with amale BNC connectorononeend and twoalligator
clipson theother end.
Model
7755 50Q Feed-ThroughTerminator: The Model
7755 isa BNC to BNC adapter that is terminated with a
50Qresistor. VSWR is ~1.1, DC to 2SOMHz.
1.8 SPECIFICATIONS
DetailedModel 3910 specificationsmaybe found in Ap-
pendix
B.

SECTION 2
Getting Started
2.1 INTRODUCTION
This sectionscontainsbasic information on installation,
powerlineconnections,anditalsoprovidestypicalsim-
ple operatingexamples.
2.2 INSTALLATION
The followingparagraphs discuss Model 3910 installa-
tion.
In particular, use adequatecarewhen installing the
unit Improperinstallation
will adverselyaffect the life,
reliability,and safetyof theunit.
The Model 3910 weighs about 7 lbs;be carefulwhencar-
ryingthe
unit ormounting it in arack
2.2.1 Installation Location
The allowable ambient temperature and humidity
rangesfortheModel 3910 are.
Operating: 0 to40°C, 10 to 905paRH
Storage: -10 to50°C, 10 to M%RH
Be suretoinstall the unit in alocation that satisfies these
temperature
and humidity conditions. Also theenviron-
ment must be free of dust and vibration, and theModel
3910 mustnot be exposedto directsunlight.
TheModel
3910uses a linefilter,butpulsenoiseorstrong
magneticorelechicfieldsmay
cause incorrectoperation
of theunit. Do not install
the unit near a sourceof pulse
noiseorstrongmagnetic
or electricfields.
Theguardontherearpanelof the
unit is designedtopro-
tect
rear panelconnectors and should notbe used as a leg
for installation. Do not stand the unit vertically on the
rear
guard because it may fall over, causing instrument
damageorpersonalinjury.
2.2.2 Cooling
The Model 3910 is .air-cooledby vents. Insufficient air
flowmaycause a component in theunittofail.Followthe
instructionsgiven
below.
CAUTION
Observe the following precautions to pre-
vent damage to the unik
Avent is provided on the bottompanel of the
unit Install the unit on a rigid, flat surface,
and avoidinstalling it on soft material such
as a cushion. Be careful not to insert foreign

SECTION 2
Gefting Started
materialbetweenthe bottom of theunit and
the surfaceunderneath . Anothervent is lo-
catedon the top panel of the unit. Be careful
nottoblock the topvent by placing an object
on top of the unit.
Avoid mounting two or more
units verti-
cally.
Placing oneunit on topof anotherwill
obstructthevents.
2.3 LlNE POWER SUPPLY
The Model 3910 operates with a 100V, 120V, 220V, or
240V zklO%, 48 to 62Hz, single-phase AC powersupply.
Thepower consumption
is approximately 25VA.
2.3.1 LINE Voltage Selector Switch
The LINE voltageselectorswitch on the rearpanelallows
you to change operating voltage of the power supply.
Thestandardsettingof theswitch
is the same as thevolt-
ageavailable
in thecountryto which theunit is shipped.
Tochangethepower
supply voltage, firstdisconnectthe
linecord,
and setthesupplyvoltageswitchin thecorrect
position. Wait at least
five seconds before turning the
power
back on afterturningit off.
WARNING
To avoid a shock hazard, disconnect the
power cord from the instrument before
changing the supplyvoltage setting.
CAUTION
Be sure to set the linevoltage switch to the
correctpositionforthelinepowervoltageto
beused. Operatingtheinstrument on
an in-
correctvoltagemaycausedamagetotheunit.
2.3.2 line ReceptacleConnection
Connectthe suppliedpower cord to therear panel Line
receptacleand
to a grounded AC power receptaclesup-
plying thecorrectvoltage.
WARNING
The Model 391 0 is equipped with a 3-we
power cord that containsa separate
ground
wire and is designed to be used with
groundedoutlets.When proper connections
are made, instnunentchassis is connected to
the powerlinegmund. If the AC outlet is not
grounded,
the rear panel ground terminal
@ must be connected to safety earth
ground using #18AWG (orlarger) wire be-
fore
use.
2.3.3 Line Fuse
The line fuse, which is integral with the power line recep-
tacle, protects the instrument from over-current situ-
ations.Toreplace the
fuse, firstdisconnectthe he cord,
thenpry out the fusecompartment(immediatelyto the
right of the
FUSE marking) with a smallscrewdriver. A
spare fuse is located in thecompartment with thefuse be-
ingused.Replacetheblownfuseonlywiththetypelisted
in Table 2-1, thenreplace the fuse holder.
WARNING
To avoidashockhazard, disconnecttheline
cord
from the instrument before replacing
the
fuse.
CAUTION
Use only a fuse of the rating listed in Table
2-1, orinshument damage may occur.
Table 2-1. Fuse Replacement
Line Voltage Rating Part No.
lOOV, 120V FU-96-2
220,240V FU-96-2
NOTE Fuses are5 x 20mm and have 2SOV, normal blow ratings.
2.4 HANDLING PRECAUTIONS
When thefrontpanelor case becomes dirty, deanit with
a soft cloth. If thepanelor case is too dirty for cleaning
witha
dry cloth,dampenthecloth in mild detergent, and
wipe the panel or case with the damp cloth. Never we
solvents such as thinner or benzene, or chemical dust
clothstoavoiddamaging
the case orfrontpanelsurfaces.

2.5 BASIC OPERATlON
tailedinformationoneachoperatingfeature,referto Sec-
tion 3.
The followingparagraphssummarizefrontpaneloperat-
ing controls, give typical test connections, and discuss
typical operatingexamplesfor the Model 3910.
2.5.2 Typical Test Connections
Figure 2-2 showstypical tests connections between the
2.5.1 Front Panel Summary
Model 3910 main synthesizer and a DUT. Note that 50Q
characteristicimpedance cables such as the Model 7051
Figure 2-1 summarizes eachfront panel feature. For de- should
be usedfor outputconnections.
Figure 2-1.
Front Panel Summa y
.

SErnON 2
Getting Started
Model 391 0
SrlOnnmolrsmmsrw
~~~~~
" =a----
DUT
Q 8 B
-
/
-
- 50R BNC Coaxial cable
(Mode1 7051 or equivalent)
FCTN
OUT
Figure 2-2. Typical Connections
2.5.3 Operating Examples
The following examples give step-by-step instructions
forsettingbasic Model
3910 operating parameters. The
Model 3910
can be connected to an osdloscope to view
theresults of thevariousoperatingexamples.
Example
1: Selecting the Waveform Type (Function)
Thefirstsequencewill adjusttheModel
3910 to outputa
sinewave, with
a continuoussweep.
1. Press DISPLAY SELECT to indicate frequency
(lowerLED).
2. Press FCTN to cycle through the five options until
the LED indicatesa SINE wave (top LED).
3. Press MODE toindicate COW (continuoussweep).
Example
2: Setting the WaveformFrequency or period'
This sequence will set the Model 3910 to a frequency of
500Hz, without regard to any previous setup. You will
have to determinewhetherto use step 1 or 2 in this se-
quencebecausethere
is no way to know whatsetupwas
used for the previous test. Since the Model 3910 retains
onlyonesetting
in memory,thatsetting is alwaystheIast
one.
1. If the displayshows a frequencyhigherthan500Rz,
use
this next sequence.Otherwiseskip to step 2.
A. Movethecursorto theseventhposition:Thesev-
enth position, 100Hz column,
will blink. Press
the
CLEAR key and at the same time press the
left cursorkey.
All digitsto the left of the blink-
ing digitwill retum to 0(erase).
B. The seventh position, lOOHz column, will be
blinking. Rotate the MODIFY knob UP (clock-
I
wise)toincreaseor DOWN (counter-clockwise)
to decreasethedigittothecorrectvalue,
5 in the
lOOHz column.
C.
If any ofthe lower digits (lesssignificantdigits)
in the displayed number are above zero, press
the
CLEAR key and at the same time press the
right cursor key.
All digits to the right of the
blinking digitwiIlreturnto0. ThedispIayshould
now show the following digits: 5000000
(m.ooooHz).
2. If the display shows a frequency less than 50lX-I~
(5000000),use this sequence:
A. Assume the display indicates a frequency of
86Hz. Presstheleft, orright, cursorasnecessary
tomake
the columnto theleftof 8 blink. A u will
appear in ihii column.
B. Rotate the MODIFY knob UP (clockwise)and a
numberwillappearinthelOOHz column.Adjust
this number to 5.
C. Pressthe CLEAR key andat thesametimepress
theright cursorkey.
All digitsto the right of the
blinkingdigit
will returnto0.Thedisplayshould
now show the following digits: 5000000
(m.0000Hz).

NOTE
Thefrequencymay be increased quickly, us-
ing theabovemethod,butnosimilaraction is
"
availabletorapidlyreducethefrequencyset-
ting.
Example 3: Setting the Output Amplitude
This stepsetstheamplitudeof theexistingwaveformtoa
valueof IOmVp-p:
Use
the cursordownkey tosettheamplituderangesoit
indicates0.02Vp-p (20mVp-p). Rotate the
AMlTD knob
until the scopeindicatesIOmVp-p.
Example 4: Changing the Output to a Square Wave
This examplechangesthe output to a squarewavewith
variable duty cycle, while maintaining the present fre-
quency,
in continuousmode.
1. Press FCTN twicetoindicateasquarewave output.
Note that the output waveform
has equal time-on
and time-off.
2. Press DUTY VAR to allowvariableduty cyde (LED
on). Rotatetheassociatedknobbelowthekey to cre-
SECTION 2
Getting Stnrted
ate squarewaves with different on- and off-times.
Leavethesquarewave
in someextremevariablepo-
sition;that
is, an obviouslyunequal on- oroff-time.
3. Press DUTY VAR keyagain.Thescopepresentation
reverts to
a square wave with equal on- and off-
times.
4. Press the DUTY VAR key again. The scope should
display the unequal duty
cycle from the previous
step.
Example 5: Adjust the DC Offset
This stepadjuststhe DC offsetvaluebased on thecenter-
line (zero or average) voltage level of the
existing
waveform.
I. Pressthe DC OFFSET key (LED on).Rotatetheasso-
ciatedknob
and note the verticalmovementof CH A
on the scope. This movement corresponds directly
with theoffsetvoltageappliedby therotationof
the
knob. Leave the signal with a sigruficant offset and
go to thenext step.
2. Press DC OFFSETagain (LEDoff).Thescopepresen-
tation reverts to the original value of zero offset.
Press thekey again
and the offset valuere-appears
andthe
CH A displaymoves off zero. Press the key
once more to return the scope to zero offset (LED
0fO.