Keithley 485 User manual

MODEL 485
AUTORANGING PICOAMMETER
QUICK REFERENCE GUIDE

INTRODUCTION
This reference and programming guide contains condensed specifica-
tions and information which describes the various features of the
Model 485. Each feature is described in three segments of informa-
tion. The first segment describes the features. The second segment
gives an exact procedure on how to use the feature. The third seg-
ment gives application examples. These segments are brief, but the
information presented in this format is designed for a quick reference
of the Model 485 features and functions. Refer to the Model 485 In-
struction Manual for complete information and essentialsafety infor-
mation.
With the Model 4853 IEEE-488 interface installed, the Model 485 can
be controlled over the IEEE-488 bus. This booklet also contains infor-
mation concerning Model 485 bus operation. Several example pro-
grams using some commonly used controllersare outlined to get the
Model 485/4853 “up and running”.
CONTENTS
CONDENSED SPECIFICATIONS .......................... 2
MODEL485 FEATURES ................................... 5
IEEE-488 PROGRAMMING.. ............................. 13
PROGRAMS ............................................ 18
IBM-PCorXTPersonalComputer.. ....................... 19
(Keithley Model 8573 Interface)
APPLE II (Apple Interface) ............................... 21
HP-85 ................................................. 22
HP-9825A.. ........................................... 23
HP-9816 ............................................... 24
HP-9845B.. ........................................... 25
TEK4052 .............................................. 26
DECLSIll.. ......................... ___. .......... _.- 27
PETlCBM2001 ........................................ 29
EH7000 Computer ..................................... 30
01984. Keithley Instruments, Inc.
Cleveland, Ohio, U.S.A.
Document Number: 485903-OlA
1

CONDENSED SPECIFICATIONS
Range
2nA
20 nA
2OilnA
J
Resolution
O.lpA
1 PA
10 pA
100 nA
1llA
10 nA
100 nA
Accuracy (1 year) Maximum
18O-2WC Continuous
*(%rdg + countsIt InputS
0.4 + 4 35OVdc
0.4 -t 1 35OVdc
0.2 + 1 35OVdc
0.15 + 1 35OVdc
0.1 +1 5OVdc
0.1 +1 5OVdc
0.1 +1 5OVdc 1
W&h no limitiw resistance: 1OOOVdc with external lOOk series resistance.
INPUT VOLTAGE BURDEN: Lessthan 2OOhV.
RANGING: Manual or autoranging.
AUTORANGING TIME: 2COmsper range.
SElTLING TIME AT DISPLAY: Lessthan lsec to within 1cuunt after
ranging.
CONVERSION PERIOD: 300ms.
TEMPERATURE COEFFICIENT: -z f0.1 x applicable accuracy
specificationper T.
MAXIMUM COMMON MODE VOLTAGE: BOVrms, DC to 60Hz
sinewave.
ANALOG OUTPUT:
Output Voltage: +lV, = -10000 counts. (Except +lOOmV =
-1OoM) wunts on 2nA range.)
Output Resistance: 1OOOQ.
RELATIVE: Pushbutton allows zeroing of on range readings. Allows
readings to be made with respect to baseline value. Front panel
annunciatorindicatesREL mode.
DATA STORE and MINIMAX: 100 readingstoragecapacity. Records
date at one of seven selectable rates from Brdgs/s to lrdg/hr and
manual triggering. Also detects and stores maximum and minimum
readingscontinuouslywhile in the data store mode.
LOG: Displaysthe logarithm(base10)of the inputcurrentreferencedto
1A.
2

SAFETY SYMBOLS AND TERMS
The ayrnboj
Q I on the instrument denotes that user shouldrefer to
the operating section in the Model 455 InstructionManual.
The WARNING usedinthisguideexplainsdangers that could resultin
personalinjuryor death.
SAFETY PRECAUTIONS
1. Before operation, ground the instrument through a properly earth
grounded power receptacle.
2. Before servicing,disconnectthe instrumentfrom the power line, all
other equipmentand consultthe Model 455 InstructionManual.
3. Do not touch the inputterminalwhile the instrumentisturned on or
connacted to any other tast equipment. Commonmodevoltagemay
be prasent.
3

DISPLAY ANNUNCIATORS
the fol\owing annunciators are displayA on the LCD Kiquid Crystal
Display1
AUTO-Indicates that the h+nfel485 is in the autorange mode.
REL--lnticates that the relativemodeisselecttxl. The readingisr&t&
to some previousreading.
LOG-Log mode readingisdirectlyin log (base 101.
SO-Indicates that the data store and minimax hold function is run-
ning. Displayedraadjng ispresent input.
RCL-Indicates that the displayedreadingis recalleddata.
BAT-Indicates that the battery requires recharghg (operates only if
the battery pack option Model 1758, is instaliedl.
ZERO CHECK-Indicates that the Model 485 is in the zero check
mode. Input impedancechangeswhen inthe zero check mode.
nA, & or mA-Nanoamps, microamps or milliampsselected. Read
measurementdirectlyfrom the display. (e.g. 1.2345fll
RMT--(Remote) Model 485 is beingcontrolledover the IEEE-488 bus
(Model 4853 installed).
CAL-Indicates that the Model 435 isin the calibrationmode.
4

MODEL 485 FEATURES
RANGE t2nA to 2mAl
I z&v I 35ov 5ov 5ov 5ov
MAX MAX MAX MAX
Description
The range buttonsse&t the desiredrange of current measurementfor
the Model 485. The range may’be selected manuallyor automatically.
With manual range selection always use the range that allows the
greatest amount of resolution.
Operation
Manual
1. Determinesignalto be measured.
2. Pressappmpriate range button.
3. Apply signal.
Auto
1. Pressthe AUTO button.
2. Apply signal.
5

ZERO CHECK
DesctiptIon
The ZERO CHECK button is used to correct interna ofFsetsand also
protects the sensitiveinput circuitryfrom buildup during overloads. In
the zero check mode or input overload, the input impedance of the
Modal 495 is changed as outlinedin the followingtable.
INPUT RESISTANCE WITH ZERO CHECK ENABLED
Current Maximum Effective
Ranae lmut Resistance
2nA 1 1GMl
Impedance In
Zero Check/Overload
9MWX3IpF
1. Select range.
2. Depress ZEFtOCHECK. The ZERO CHECK button operatas on the
push-pushprinciple.That is, pressingin the button locksthe instru-
ment inzero check, pressingthe button againreleasesthe zero check
mode.
Typical Use
Used in zeroing the2nA range for precise measurements. Refer to
paragraph 2.72 in the Model 495 InstructionManual.
6

REL (Relative Function)
REL
I
Description
The relativefunctionservesasa meansof baselinesuppressionallowing
a storedoffset valueto be subtractedfrom subsequentreadings.When
the REL button is pressed, the instrumentstores the baselinereading
with the next conversion. All subsequent readings represent the di-
ferences between the applied signalleveland the stored baseline.The
stored baselinecan be as smallas the resolutionof the instrumentwill
allow or as large as full range.
It isimportantto note that the RELfunctionreducesthe dynamicrange
of measurementsby that level (stored baseline). For example:assume
that the RELlevelis + Id and the Model495 ismanuallyset to thew
range. The maximum positivedisplayed reading, before overranging,
would be + 0.9999& Thisisbecausethe A/D converterwould be see-
ing + 1.9999fi to + 0.9999fi (2.999&A) as compared to the normal
-1.9999fi to + 1.9999d (3.9998fi). Actually, the dynamic range is
reduced by lfi or 10,000 counts. The effects on dynamicrangecan be
reduced by selectinge higher range or usingautorange.
Operation
1. Select measurementmodeand range. Forexample:normalmeasure-
ment mode and the w range.
2. PressREL. The displayreads zero.
3. The value that appeared on the displayis now the stored offset.
Typical Use
1. Nullingout external source offset (e.g. calibratoroffset).
2. Nulling out desired levels of offset (e.g. electrode dark current of
phototube).
7

LOG (Log Function)
Description
The log function givesthe log (base 101of the measuredinput current
referenced to 1A. Log can be used to make any current levelthe 0.0
(zero) point for log measurements. This can be done by selecting
autorange and log. Then measuringthe desiredcurrentthat isto be the
0.0 [zero) point. The logarithm is taken on the absolute value of the
measurement so that both positive and negative currents can be
displayedas e log. Pressthe REL button and the displaywiil read 0.0
(zero). The measured current is now the 0.0 (zero) point for the log
function. The mathematical equation for the log function is shown as
follows:
Input
Display = Log -
I I
1 Amp
Operation (referenced to IA)
1. Select the auto range mode.
2 Apply the source.
3. Pressthe LOG button. The LOG annunciatoron the displayturnson.
4. Take the log readingfrom the display.
Typical Use
1. For use in measuringe wide range of current. Nuclear reactorshave
variousoutputsof currentthat could be compressed(inreadingson-
ly) by usingthe log function.
2 Measuring the current output of a phototube. REL can be used to
nu[lthe dark current of the phototube.

DATA STORE (100 Point Data Store1
Description
The 100pointdata storefunctionservesto saveupto 100pointsof data
at the rate of one of six selectable rates from every reading (3 per
second) to one reading per hour. Also, manual data entry is available
(RN. This feature is usefulin applicationswhere data is requiredto be
logged over a periodof time.
Operation
1. Connect desiredmeasurement configurationto the Model 485.
2. Select rate of storage and begin data store:
A. Pressand hold in the STO/CLR button.
6. The rates are scrolled on the display. Tithe rates are described
below).
C. Releasethe STWCLR button when the desiredrate isdisplayed.
D. The ST0 annunciator turns on indicatingthat the data is being
stored at the selected rate.
Typical Use
1. Saving data pointsof current driftof a low leakagedevicesuch as e
FEr.
2. Monitoringand saving current levelsthat fluctuate over a period of
time.
r = 0 (every reading)
r = 1 (1 reading per second)
r = 2 (1 reading per 10 seconds)
r = 3 I1 readingper minute)
r = 4 I1 reading per 10 minutes)
r = 5 (1 reading per hour)
T = S (everytime STOKLR is pressed)

STO/CLR (Store end Clear Function)
Description
The STOKLR button isan internalpart of the data storefunction. The
button has severalfunctions that are listadas follows:
1. Starts the data store operation.
2. Turns off the data store operation.
3. Selects the storage rate.
4. In the R6 data rate mode the STOKLR button (when pressed)trlg-
gers the Model 485 to store a reading.
5. In the talk onlymode, the STOKLR button selectsthe talk rate. The
store mode must be disabledfor this function.
Operation
1. Pressthe STOKLR button to startthe data storeoperationISTO an-
nunciatoron the displayisturn on). At thispointthe Model465 starts
storing readings.
2. Holdinthe STOKLR button to selectthe storage rate. The ratesare
scmlled on the display. Release the STOlCLR button when the
desired rate is displayed.
3. Pressthe STOKLR button to stop the data store operation. Alldata
is retained untile new store cycle has commenced.
4. When in the R6 data rate mode, prass the STOKLR button each
timea readingisto be stored. This data rate mode isusedfor custom
rate data storage.
5. Using the IEEEinterface the STOKLR button can be usedto select
the talk rate. Refer to page 17.
10

RCL (Recall Function of DATA STORE)
Description
The RCL button is used to retrievedata that has bean stored usingthe
store/clear function.
Operation
1. Pressand hold in the RCL button. The displayscrollsthrough the
data points and minimum/maximum readings. The first data point
displayedisthe laststored reading. The next two data pointsare the
HI and LO readings made during that store cycle. Notice that the
longerthe RCL button is held in the faster the data pointsscrollon
the display.
2. Release the RCL button at the desired data point and note the
readingon the display.The data pointercan be incrementedbysteps
of one by momentarilyholdingin the RCL button.
3. Turn off the data store by pressingthe STO/CLR button. All stored
data is retained untila new store cycle has commenced.
MidMax HOLD
Description
The minimum/maximumholdfeature detectsand holdsthe highestand
lowestreadingswhileinthe data storemode. This action isindependent
of the storage rate and runsat a rate of three readingsper second. This
function works in conjunctionwith the data store mode. The minimum
and maximumreadingsare continuouslyupdatedwhileinthe data store
mode.
Operation
1. Use the data store mode to save a number of readings.
2 Pressand hold in the RCL button. The displayscrollsthrough the
data pointsand the minimumlmaxlmumpoints. The first data point
displayedis the last data point that was stored. The next two data
points are the maximum and minimum readings made during that
store cycle.
3. Releasethe RCLbutton at the desireddata point(min,max or nomral
data point)and note the readingon the display.The data pointercan
be incremented by steps of one by momentarilyholdingin the RCL
button.
Typical Use
Save up to 100 pointsof output currentdata alongwith the minimum
and maximum readingsof 1pA source that needs to be verifiedfor
calibration.
11

DIGITAL CALIBRATION
~ha diiitat calibrationfeature eliminatescalibrationpotentiometers. All
calibrationfactorsfor each rangeare storedinnon-volatileRAM;The rn-
strument can be calibratedfrom the front panel or with the optional
4353 IEEEinterface. With the Model 4653 IEEE-488 interface installed,
the Model 465 can be calibrated much faster using an automated
system. Front panel digitalcalibrationisoutlinedas follows:
NOTE
The following is an actual calibrationprocedure for
the 2Ofi range. If recalibrationisnot necessary,then
do not movethe calibrationjumper. Leavethe jumper
inthe disableposition.Referto the MaintenanceSec-
tion of the 465 InstructionManual for jumper place-
ment.
1. Move the calibrationjumper to the enable position.
2. Turn on the Model 465.
3. Press the REL and LOG buttons simultaneouslyuntil the message
“CAL” is displayed. Releasethe buttons. The Model 465 is now in
the calibrationmode as indicatedby the “CAL” annunciator.
4. Apply the proper signal or level to the Model 465 input. Example:
place the Model 465 to the 2Ofi range and apply 19.066~.
NOTE
Consultthe Model465 InstructionManualfor detailed
methods of creatingthe proper calibrationlevels.
5. Adjustthe displayaccordinglywith the usaof the STOKLR and RCL
buttons. The STOKLR button increments the displayed reading.
The RCL button decrements the displayedreading.
6. Press the LOG and REL button simultaneouslyuntil the massage
“STOR” isdisplayed.The “new” calibrationpointforthe 2&A range
is now permanently stored. This new constant remains as is until
changad.
7. To return to normaloperation, turn off the instrumentmomentarily,
then back on.
8. Turn the instrumentoff and placethe calibrationjumper inthe disable
positionto prevent inadvertent calibrationof the instrument.
Consultthe Model465 InstructionManual for completedetailsconcern-
ing Model465 calibration.The precedingprocedureispresentedhereto
remind the user that front panel digital calibrationis availableon the
Model 465.
IEEE-468 option: Allows the user to calibratethe instrumentover the
IEEE-468 bus. With the IEEE48 interface installed(option4653). the
Model 465 can be calibratedon most automated calibrationsystems.
12

IEEE-488 PROGRAMMING
Tha K&hlay Model 485 hasan optionalIEEE-488interfaca(Model
4853) which can be includedwith the instrumentor added later.
Inclusionof the interfaceoptionisapparent by the connectorand
addressswitch at the rear panel. The fieldinstallableoptionkit in-
cludesa replacementtop cover with appropriateaccessopenings
on the rearpanel. The followinglistsallthe commandsavailableto
the Model 485.
RANGE:
LOG:
RELATIVE:
ZERO CHECK:
TRIGGER:
EOI:
STORE:
DIGITAL
CALIBRATION:
SRQ:
RO = Auto Range
(ROignored in calibrationmode)
Rl = 2nA
R2= 20nA
R3 = 200 nA
R4= Z/UI
R5 = 20/A
R6=266d
R7= 2mA
W=Off
Dl = On
M=Off
21 = On
CO=Off
Cl = On
To = Continuouson Talk
Tl = One-shot on Talk
T2 = Continuouson GET
T3 = Oneshot on GET
T4 = Continuouson “X”
T6 = One-shot on “X”
KO = EOI is transmittedon the last byte
out.
Kl = EOI is not transmitted.
L6 = Store CalibrationConstants
V+n.nnnnE+nn
n= CalibrationValue
Mnnn
nnn= 0 to 255(base 10)
MO = Clear SRQ data mask
Ml = Reading Overflow
ME = Reading Done
M9 = Reading Done or ReadingOverflow
13

Ml6 = Busy
Ml7 = Busy or ReadingOverflow
M24 = Busyor Reading Done
M25 = Busy, Reading Done or Reading
ovemow
P.432= Clear SRQ Errol mask
M33 = IDDCQ
M34 = IDDC
M35 = IDDC or IDDCO
M36 = Not in Remote
M37 = Not in Remote or IDDCO
M33 = Not in Remota or IDDC
M39 = Not in Remote, IDDC or IDDCO
STATUS WORD: UO = Output Status Word on next read.
DATA FORMAT: GO = Send Prefuc
Gl = Do Not Send Prefix
TERMINATOR: Y(ASCII) = ASCII character
Y(CR LF) = CR LF
YiLF CR) = LF CR
Y(X) = None
EXECUTE: X = Execute other device-dependent
commands.
POWER UP DEFAULT CONDITIONS
LOG
REIATNE
CALIBRATION MOM
TRIGGEFI
EQI
DATA FORMAT
VALUE/STATUS
Turned Qff
Reflects Front Panel Buttons
Reflects Front Panel Button
Do) off
m off
w
(TO)Continuous on Talk
(KC0EOI is tranm-iti cm last byte
out.
(MOOO)No SRQ
Standard Output
(GO1Prefix Enabled
(CR) ILFI
14

MODEL 4953 PRIMARY ADDRESS SWITCH SET AT 22 (10110)
TALKER ONLY
(TO) MODE
:1pljijJpg
1 ADDRESSABLE
MODE
DATA FORMAT:
(Reading)
NDCA * 1 .2345 E-9 CR LF
1 ~iiiti&.%@
N = Normal
0 = Overflow
C = Zero Check
Z = Relative
15

STATUS:
485 CDRZKT MdMeY CR LF
r 7YzJLsIgdl,D.
DEFAULT:
4 8 5 C x D 0 R x Z 0 K 0 T 0 M 0 0 0 (CR) ILFI
R.sfk?cts
Front Panel
Reflects . 1
Front Panel
16

Talk Only Operation
Description
The talk oniymode maybe usedto senddata to a listenonlydevicesuch
as a printer. When the Model 465 is in the talk only mode, it ignores
commandsgivenoverthe bus. The talkonlymode isenabledby placing
the TOlADDRSSABLE switch in the TO position and then cycling
power to the instrument.The default talk rate isthree readingsper se-
cond (everyreading). However, a different talk rate can be selectedby
performingthe followingprocedure.
Operation
1. Enablethe talk only mode. Cycle power to the instrument.
2. Pressand holdinthe STOKLR button. The followingtalkratesscroll
on the display:
r = 0 (every reading)
r = 1 (1 readingper second)
r = 2 (1 reading per 10 seconds)
r = 3 (1 reading per minute)
r = 4 (1 readingper 10 minutes)
r = 5 (1 readingper hour)
r = 6 (1 reading per everytime STOKLR is pressed)
3. Releasethe STOlCLR button when the desiredtalk rate isdisplayed.
At this point the ST0 annunciatorappears on the displayindicating
that the instrumentis talking at the selected rate.
4. Turn off the data store operationby pressingthe STOKLR button.
Notice that the ST0 annunciatorturns off. ,
NOTE
The instrumentremainsin the selected talk rate untila
new rate isselected or power is cycled.
17

PROGRAMS
The fallowing programs are designed to be a simple aid to the war.
They are not intended to suit specificneeds. Detailed programmingin-
formation can be found in the manual.
These programsdisplayone readhg at the output of the controller.The
program providesan ASCII stringvariableoutput of the form:
NDCA + O.DoOO+OCR LF
The note at the end of each programindicatesmodificationsto provide
a numeric variable(A) in exponentialform:
+o.ooao+o
18

IBM PERSONAL COMPUTER XT or PC
(Keithley Instruments Model 8573 GPIB Interface)
The followingprogram sendsa command stringto the Model485 from
an \BM PC or XT computer and displaysthe instrumentreadingon the
CRT. The computer must be equipped with a Keithley Instruments
Model8573 GPIB IEEEinterfaceand the DOS 20 operatingsystem.The
GPIB software and hardware must be configured per the KeithleyIn-
struments Model 8573 InstructionManual.
DIRECTIONS
1. Using the rear panel switches set the primaryaddressof the Model
485 to 22 (10110).
2 Wti the power off, connectthe Model485 to the IEEE-488interface
installedin the IBM computer.
3. Usingthe interfacesoftware IBCONF program,set upthe GPIB.COM
handlerso that “DEV22” hasa primaryaddressof 22 Again, consult
the interface board instructionmanualfor complete details.
4. Place the instrument software disc in the default drive, type LOAD
“DECL”, and pressthe return key.
5. Enter the followingprogram into the computer, pressingthe return
key after each lineistyped. Linesl-6 are part of the DECLprogram
previouslyloaded and naed not be typed in.
6. Run the program and type in the desired command string when
prompted. Forexample:to placethe Modal485 intothe one shot on
talk triggermode and in the &A range, type inTl R4X and pressthe
return key.
7. The displaywillshow the Model 485 readingstringon the CRT. For
example:when the Model 485 isin Zero Check, the displaywillread
NDCA + O.OOOOE-6.
8. To exit the program type EXIT and pressreturn.
PROGRAM
1 CLEAR ,160OOl
2 IBlNlTl = 160001
3 IBINlT2 = IBlNlTl + 3
4 BLOAD “BIB.M”IBINITl
5 CALL IBINITl(IBFIND,IBTRG,
BCLR,IBPCT,IBSIC,IBLOC,
IBPPC,IBBNA,IBONL,IBRSC,
IBSRE,IBRSV,IBPAD,IBSAD,
IBIST,IBDMA,IBEOS,IBTMO,
IBEOTI
6 CALL IBINITZ(lBGTS,IBCAC,
IBWAIT,IBPOKE,IBWRT,
IBWRTA,IBCMD,IBCMDA,
COMMENTS
GPIB-PC Rev. B.0
IBM BASICA Declaration
File.
19