Keithley 485 User manual

Model 485
Autoranging Picoammeter
Instruction Manual
Contains Operating and Servicing Information

WARRANTY
Keithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for a period of 1 year from date of
shipment.
Keithley Instruments, Inc. warrants the following items for 90 days from the date of shipment: probes, cables, rechargeable batteries,
diskettes, and documentation.
During the warranty period, we will, at our option, either repair or replace any product that proves to be defective.
To exercise this warranty, write or call your local Keithley representative, or contact Keithley headquarters in Cleveland, Ohio. You will
be given prompt assistance and return instructions. Send the product, transportation prepaid, to the indicated service facility. Repairs
will be made and the product returned, transportation prepaid. Repaired or replaced products are warranted for the balance of the origi-
nal warranty period, or at least 90 days.
LIMITATION OF WARRAN-IY
This warranty does not apply to defects resulting from product modification without Keithley’s express written consent, or misuse of
any product or pwt. This warranty also does not apply to fuses, software, non-rechargeable batteries, damage from battery leakage, or
problems arising from normal wear or failure to follow instructions.
THIS WARRANTY IS IN LlBU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING ANY IMPLIED
WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. THE REMEDIES PROVIDED HEREIN ARE
BUYER’S SOLE AND EXCLUSIVE REMEDIES.
NEITHER KBITHLEY INSTRUMENTS, INC. NOR ANY OF ITS EMPLOYEES SHALL BE LIABLE FOR ANY DIRECT, INDI-
RECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF ITS INSTRUMENTS AND
SOFTWARE EVEN IF KEITHLEY INSTRUMENTS, INC., HAS BEEN ADVISED IN ADVANCE OF THE POSSIBILITY OF
SUCH DAMAGES. SUCH EXCLUDED DAMAGES SHALL INCLUDE, BUT ARE NOT LIMITED TO: COSTS OF REMOVAL
AND INSTALLATION, LOSSES SUSTAINED AS THE RESULT OF INJURY TO ANY PERSON, OR DAMAGE TO PROPERTY
Keithley Instruments, Inc. - 28775 Aurora Road *Cleveland, OH 44139~216-248-0400 -Fax: [phone] *http://www.keithley.com

Model 485 Autoranging Picoammeter
Instruction Manual
0 1984, Keithley Instruments, Inc.
Test Instrumentation Group
All rights reserved.
Cleveland, Ohio, U.S.A.
January 1990, Sixth Printing
Document Number: 485-901-01 Rev. F

SPECIFICATIONS
RANGE RESOLUTION
2nA O.lpA
20 “A 1 PA
200 “A 10 pA
2PA 100 PA
20 !A 1 nA
200 ,‘A 10 “A
2mA 100 “A
ACCURACY I1 YEAR,
lW28~C
* l%rdg + countslt
0.4 + 4
0.4 + 1
0.2 + 1
0.15 + 1
0.1 + 1
0.1 +1
0.1 +1
NORMAL MODE
ANALOG REJECTION MAXIMUM
RISE TIME RATIO CONTINUOUS
I10 .SO%, IS0 or EOHz, INPUTt
60ms 7OdB 350”dC
60iTlS 7OdB 350Vdc
6rnS 65dB 350Vdc
3ms 6FdB 350Vdc
3ms 65dB 5O”dc
lms 65dB 5OVdc
lms 55dB 5OVdc
,NP”T VOLTAGE BURDEN: Less than 200&V.
RANQING: Manual or autoranging.
AUTORANGING TIME: Average 250ms per range.
SmLlNG TIME AT DISPLAY: Less than 1 second to within 2 co”nts on
fixed range.
CONVERSION PERIOD: 300,“s.
TEMPERATURE COEFFICIENT 10°-160C B 26°-50”C,: f10.1 x BP-
plicable sccuracy specification) per OC.
MAwMUM COMMON MODE VOLTAGE: 30V rms. DC to 60Hz sine
WWB.
ANALOG OUTPUT:
Output Voltage: + IV = - 10000 co”ntf.. mept + 1OOmV = - 10000
mints 0” 2nn range.
OUtput tIea,*tance: 10000.
REL: Pushbutton allows zeroing of an range readings. Allows relative
readings to be made with respect to baseline value. Front panel ~nnuncistor
indicates REL mode.
DATA STORE and MINIMAX: 100 reading storage capacity: records data
at one of six selectable rates from 3 readings/second to 1 reading/hour, or
by manual triggering. Also detects and stores maximum and minimum
readings comin”““sIY while in the data store mode.
LOG: Displays logarithm (base 101of the absolute value of the measured C”F
rent Iexamples: -3.000 = *ImA; -6.301 = +O.$Al.
IEEE-488 BUS IMPLEMENTATION (Option 48631
MULTILINE COMMANDS: DCL, SDC, GET, GTL, “NT. UNL. SPE. SPD.
UNILINE COMMANDS: IFC, REN EO,. SRC. ATN.
INTERFACE FUNCTIONS: SHl. AH,, T5. TEO. L4, LEO. SRI, RL2,
PPO. DCl, DTI, CO, El.
PROGRAMMABLE PARAMETERS: Zero Check. Range, REL. LOG, Trig-
ger, Calibration. EO,, SRO, Status. 0”tp”t Format. Terminator.
GENERAL
DISPLAY: 4% digit LCD, 0.5” height: polarity. range and staf”s indication.
OVERRANGE INDICATION: “OL” displayed.
CONNECTORS:
Input: ENC.
Analog Output: Banana Jacks.
OPERATING ENVIRONMENT: 0-50.X. less than 70% R.H. up to 35’C:
linearly derate 3% R.H./OC up to 5OOC.
STORAGE ENVIRONMENT: -25O to +BO”C
POWER: lOF,-125V or 210.250V (switch selected,. go-llOV available.
SO-6OHr. 12 VA.
DIMENSIONS, WEIGHT: 65mm high Y 235mm wide x 275mm deep.
(3%” x 9%” x lO%“,.
Net Weight: 1.Skg I4 Ibs.)
ACCESSORIES AVAILABLE:
Model 1010:
Model ,017:
Model 1664:
Mods, 1758:
Model 4801:
Model 4603:
Model 4653:
Model 7006-3:
Model 7006-6:
Model 6573:
Single Rack Mounting Kit
Dual Rack Mounting Kit
Hard Shell Carrying Case
Rechargesble Battery Pack
Low Noise Input Cable (4ft.l. BNC to ONC
Low Noise Cable Kit
IEEE-486 Interface
IEEE-466 Digital Cable 13ft.b
IEEE-468 Digital Cable 16ft.1
IEEE-488 Interface for IBM PC
Specifications subject to change without notice.

TABLE OF CONTENTS
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
2.1
2.2
2.2.1
2.2.2
2.2.3
2.3
2.4
2.4.1
2.4.2
2.4.3
2.4.4
2.5
2.6
2.7
2.7.1
2.7.2
2.7.3
2.7.4
2.75
2.7.6
2.7.7
2.8
2.8.1
2.8.2
2.8.3
2.8.4
2.8.5
2.9
2.9.1
2.9.2
2.9.3
2.9.4
2.9.5
3.1
3.2
i::
3.5
SECTION l-GENERAL INFORMATION
Introduction. ........................... ...... ...... ...... ......
Getting Started ......................... ...... ...... ...... ......
Unpacking and Inspection ................ ...... ...... ...... ......
Specifications .......................... ...... ...... ...... ......
Warranty Information. ................... ...... ...... ...... ......
Manual Addenda ....................... ...... ...... . ...... ......
Safety Symbols and Terms ............... ...... ...... ...... ......
Optional Accessories .................... ...... ...... ...... ......
l-1
1-l
l-l
l-l
l-l
1-2
1-2
l-2
SECTION Z-BENCH OPERATION
introduction ...............................................................................
PreparationforUse ..........................................................................
Line Power ..............................................................................
Battery Pack Power .......................................................................
BatteryCharging .........................................................................
TntBail ....................................................................................
Model 485 Familiarization ....................................................................
Display ..................................................................................
FrontPanelControls .......................................................................
InputConnector ..........................................................................
AnalogOutputConnectors .................................................................
Error Messages .............................................................................
EnvironmentalCondition .....................................................................
BasicBenchMeasurements ..................................................................
Power-Up ...............................................................................
Zero Check ..............................................................................
Current Measurements ....................................................................
RelativeMode ...........................................................................
LOGMode ...............................................................................
Inverting Analog Output ...................................................................
MIN/MAXand 100 Point Data Store .........................................................
MeasurementConsiderations .................................................................
SourceResistance ........................................................................
SourceCapacitance .......................................................................
LeakageResistance .......................................................................
ZeroTimeStability ........................................................................
Groundingconsiderations ..................................................................
2-l
2-l
2-l
2-l
2-l
2-1
2-l
2-l
2-2
2-2
2-2
2-2
2-3
2-3
2-4
2-4
2-4
2-4
2-5
2-5
2-6
2-6
2-6
2-7
2-8
2-8
2-8
Applications ................................................. .........................
Op Amp Offset Current ...................................... .........................
FET Gate Leakage and Channel Current. ....................... .........................
Insulation Leakage Currents and High Resistance. ................ .........................
Phototube, Photodiode and Beam Currents ..................... .........................
Resistivity Tests ............................................ .........................
SECTION 3-PERFORMANCE VERIFICATION
Introduction ......................................
Environmental Conditions ...........................
Recommendrsd Test Equipment ......................
Initial Conditrons ...................................
Verification Procedure ..............................
,,....
,,....
..................
..................
..................
..................
..................
3-l
3-l
,. 3-l
3-1
3-l
i

TABLE OF CONTENTS (CONT.)
4.1
4.2
4.3
4.3.1
4.3.2
4.3.3
4.3.4
4.3.5
4.4
4.4.1
4.4.2
4.4.3
4.4.4
4.5
4.6
4.7
5.1
5.2
5.3
5.4
5.4.1
5.4.2
5.4.3
5.4.4
5.4.5
5.5
5.6
5.6.1
5.62
5.63
5.6.4
5.6.5
5.7
5.8
5.9
6.1
if
6.4
6.5
SECTION 4-THEORY OF OPERATION
Introduction ............................................................................... 4-l
Overall Functional Description. ................................................................ 4-l
AnalogCircuitry ............................................................................ 4-l
Current-to-Voltage Converter ............................................................... 4-1
Multiplexer ............................................................................4-2
InputBufferAmplifier ..................................................................... 4-2
-2VReferenceSource ..................................................................... 4-3
AIDConverter.. ......................................................................... 4-3
Digital Circuitry ............................................................................. 4-4
Microcomputer ........................................................................... 4-4
Address Decoding ........................................................................ 4-4
PIA ..................................................................................... 4-4
DisplayBoard.. .......................................................................... 4-4
Digital Calibration ........................................................................... 4-4
PowerSupply .............................................................................. 4-4
Model 1758 Battery Option ................................................................... 4-4
SECTION 5-MAINTENANCE
Introduction ............................................................................... 5-I
Top Cover Removal/Installation ............................................................... 5-l
Battery Pack (Model 1758) Installation ......................................................... 5-l
Front Panel Calibration ...................................................................... 5-l
Recommended Calibration Equipment. ....................................................... 5-1
CalibrationJumper ........................................................................ 5-2
Environmental Conditions .................................................................. 6-2
Calibration Procedure. ..................................................................... 5-2
CalibrationStorage ........................................................................ 5-2
Calibration Over IEEE-488 Bus ................................................................. 5-3
Troubleshooting ............................................................................ 5-3
Recommended Test Equipment ............................................................. 5-3
Self Diagnostic Program ................................................................... 5-3
Power Supply and Battery Pack (Model 1758) Checks ........................................... 5-6
A/D Converter and Display ................................................................. 5-6
SignalConditioning ....................................................................... 5-7
Input Amplifier NJ105) Balancing .............................................................. 5-7
LineFuseReplacement ...................................................................... 5-7
Special Handling of Static Sensitive Devices., ................................................... 5-8
SECTION B-REPLACEMENT PARTS
Introduction ............................................................................... 6-l
ReplaceableParts ........................................................................... 6-l
Ordering Information ........................................................................ 6-l
FactorySen/ice ............................................................................. 6-l
Component Location Drawings and Schematic Diagrams .......................................... 6-l
ii

LIST OF ILLUSTRATIONS
2-1
2-2
2-3
2-4
2-5
2-6
2-7
Z-8
2-9
2-10
3-l
4-l
4-2
4-3
4-4
4-5
5-I
5-2
6-l
6-2
6-3
6-4
6-5
6-6
6-7
6-8
Model485FrontPanel ....................................................................... 2-2
Model 465 Inverting Analog Output ........................................................... 2-6
Simplified Model for Input Signal Conditioning .................................................. 2-7
Test Fixture Guarding ....................................................................... 2-8
LeakageTestSetUpUsingModel6104 ........................................................ 2-8
Op Amp Input Offset Currents Measurement .................................................... 2-8
F5T Gate Leakageand Channel Currents Measurement. ........................................... 2-9
Insulation Leakage Currents end High Resistances Measurement .................................... 2-9
Set Up to Measure Photomultiplier, Photodiode end Beam Currents .............................. ,, 2-9
ResistivityTestSetUp ...................................................................... Z-IO
Shielded Test Fixture ........................................................................ 3-2
Simplified Block Diagram ..................................................................... 4-l
Current-to-Voltage Converter ................................................................. 4-2
Simplified Schematic of the Multiplexer ......................................................... 4-2
Simplified Schematic of the Input Buffer Amplifier ................................................ 4-2
AIDConverter ............................................................................. 4-3
Segmentldentification ....................................................................... 5-4
JumperLocations ........................................................................... 5-7
Model485MiscelianeousParts ............................................................... 6-2
Display Assembly ........................................................................... 6-3
Mother Board, Component Location Drawing. Dwg. No. 485-100 ................................... 6-7
Mother Board, Schematic Diagram, Dwg. No. 485-106., .......................................... 6-9
Display Board, Component Location Drawing, Dwg. No. 485.110 ................................... E-13
Display Board, Schematic Diagram, Dwg. No. 485-116 ............................................ 6-14
Model 1758 Battery Peck, Component Location Drawing, Dwg. No. 1758-100 ......................... 615
Model 1758 Battery Peck, Schematic Diagram, Dwg. No. 1768-106 ................................. 6.16
iii

LIST OF TABLES
2-1
2-2
2-3
3-1
3-2
5-1
5-2
5-3
5-4
5-5
5-6
5-7
5-8
6-1
6-2
83
8-4
Error Messages.. ..........................................
Range, Accuracy and hlaximum Allowable Inputs ...............
Equivalent Input Resistance With Zero Check Enabled ............
Recommended Test Equipment ..............................
RangeAccuracy ...........................................
Range Calibration ..........................................
Recommended Troubleshooting Equipment ....................
TroubleshootingModes .....................................
Power Supply Checks and Battery Pack (Model 1758) Checks .....
A/DConverterChecks ......................................
DisplayBoardChecks ......................................
OffsetJumparSetUp ......................................
Static Sensitive Devices ....................................
Mother Boerd, Parts List ....................................
Display Board, Parts List ....................................
Model 1758 Battery Pack, Parts List ...........................
Model485SperePartsList ..................................
.......
.......
.......
.......
2-3
2-3
2-4
3-l
3-2
5-3
5-3
5-5
6-6
6-6
5-7
5-7
5-8
6-4
6-13
6-15
6-17
iv

SAFETY PRECAUTIONS
The following safety precautions should be observed before operating the Model 485.
This instrument is intended for use by qualified personnel who recognize shock hazards and are familiar
with the safety precautions required to avoid possible injury. Read over the manual carefully before
operating this instrument.
Exercise extreme caution when a shock hazard is present at the instrument’s input. The American
National Standards Institute (ANSI) states that a shock hazard exists when voltage levels greater than
30V rms or 42.4V peak are present. A good safety practice is to expect that a hazardous voltage
is present in any unknown circuit before measuring.
Do not exceed 30V rms between the input connector shell and earth ground.
Inspect the test leads for possible weer, cracks or breaks before each use. If any defects are found,
replace with test leads that have the same measure of safety as those supplied with the instrument.
For optimum safety do not touch the test leads or the instrument while power is applied to the circuit
under test. Turn the power off and discharge all capacitors, before connecting or disconnecting the in-
strument.
Do not touch any object which could provide a current path to the common side of the circuit under
test or power line (earth) ground. Always make measurements with dry hands while standing on a dry,
insulated surface, capable of withstanding the voltage being measured.
Do not exceed the instrument’s maximum allowable input as defined in the specifications and operation
section.
Safe operation and good measurement practice dictates use of an external resistor when necessary to
limit input currents to less than 3mA.

Model 485 Addendum
me following idormation is supplied as asupplement to tfi manual korder to prmide the user
with the latest tiprovements. It is recommended that vefication tio~tion kadded to Section 3
of the Model 485 Instiction Manual and c&bration tifomatimr be added to Section 5.
~is addendum contatis complete procedures for vefi@g and cahhatig the Model 485 ustig the
WltMq Model 2& Cdibmtor/Somce. Complete sepmate pmcedmes apmtided for @otig di@ti
calibration horn either the hont panel or over the IEEE+8 bus. Dgitd ctibration over the bus is
automated ustig aBASIC pro~am mn @the W85 computer.
PA-2w Rev. A/149

PERFORMANCE VERIFICATION USING
MODEL 263 ~LIBRATOR/SOURCE
Use of the Model 263 to verify ac~aq specifications of
the Model 485 stip~ies the prored~ by etiating the
need for user desi~ed _nt somces. The quipment
fisted hTable >1 of the manual is not needed.
Idetiy performance verification shotid be perfomed
when the tis~ent kfirst received to emm that no
daage or chmge hcalibration has ocmed dtig ship
ment. It may&O be perfomed when fi~ent acwa~
is swpe~ Orfo~w~ c~bration. Eperfmrnance on any
of the rmges ia outside the specified tits, ctibrate the
titiment.
NOTE
Mthe~ent does not meti spedicatiom md
is stfl under warrmty ~ess thm Qmonths stice
date of shipment), con~d your ~lMey mpmsen-
tative Orthe factory bdetetie the atimr to &
t&en.
Etimenti Condltiom
Mmeasurements shodd be made at mmbient
temperature b~een M“ md 28°C (&” to 82°~ with a
relatiw humidity less thm 70°h.
Irritid Conditimra
Before perfofig the verification procedure, m&e sure
the Models 485 md 263 meet the fo~owtig conditiom:
1Ethe tis~ents have been subjed btempmams
blow M°C (&°F) Orabom 28°C (82°F), dow sufficient
tie for the titruments to reach temperahs tithti
the rmge. GenerWy, it tskes one hour to stabtie m
irrs~ent that is M“C (MOF)outside of the specfied
range.
2. Tm on the Models 485 and 263, and allow them to
wm up for one hour. The Model ~may be operated
from either ~ie power or battery pack power, as long
as the batteq pack has been fu~y charged..
Veficatirur Prncedw
Weed as fo~owsto verify the accuraq of the Model 485:
1. On the Model 485, press ZERO CHECK and select the
Mrmge.
2. With an open input, adjust the ZERO pot for .0000 *1
cmrnt on the display.
3. Comect the Model 263 to the Model 485 as shown in
Fi~e 1. Make sue the cdlbrator is in standby.
4. Relesae ZERO CHECK on the Model 485.
5. Using the AMPS (adive) c~nt source, program the
Model 263 to output 1.90~nA and verify that the
reading is within the Itits hTable 1,
6. Using Table 1as aguide, check the rest of the current
ranges by applying the a~ropriate current and verify-
ing that the reatig is within the allowable limits.
Table 1. Range Accumcy
263 Output
(AMPS)
1.90M0 A
19.0000 M
190.WO A
1.90000 PA
19.0000 ~A
190.000 @
1.9oooofl
*Includes Model 263 error.
Allowable Reading*
(M”C -28°C)
1.8933 to 1.9067
B.936 to 19.064
M9.69 to 190.31
1.8976 to 1.9024
28.986 to 19.014
E9.86 to lW.14
1.8986 to 1.9014

MODEL 4W BNC TO TRIW ADAPTER
\
MODEL 263 MODEL 485
Rgum 1. Model 485 Verification Connections
.

CALIBRATION USING MODEL 263
CALIBRATOWSOURCE Environmental Conditions
me fo~oting pua~aphs ptide detded pmcedwes for
c~bratig the Model 485 Picommeter using the Model
263 Wbrator/Some. Mbut one of the cfibratimr ad-
jmtienta ~e digiti md ~&done km the ~nt pmel
mover the ~EE~ bus.
TOc~brate the tis~ent bm the tint pmel, pefiom
the fo~otig pmedures, muitig pma~aph ‘TEEE=
BW Cfibration”. TO ctibate the Model 485 over the
=4 bus, pdom the foflwtig pmedmes, ornitig
pmagaph ‘Tmnt ~el Mbration”.
Calibmtion Stomge Enable
The Model 485 mmt be in cfibratimr storage enable to
stem cfihation comtita hNVRAM. Ethe instiment
knot placed hti mode, subsequent ctibration Wbe
lost when the ~at kbd off. @fiOm the fOflw-
~g steps tO enable cab~mtiOn stOrage.
1. Mthe Model 485 is presently rm, *it off.
2. We holtig kthe S~/CLR button, -the ina~-
ment back on.
3. When the “CA~ message is displayed, mle=e the
~/CLR button. The ina~ent ti ~to the rmr-
md diapl~ mode md the stotig of cdibratimr con-
s~ts is now enabled.
Required Equipment
The fo~-g item (one of each) me necess~ ti ctihate
the Model ~:
1. WitMq Model 263 Cti&ator/Some.
2. Trim to Tri= Cable (suppfied with 263)
3. kiW~ Model WMde BNC to Pemde Tfi Adapter.
N~: The fo~owtig ad~tiond item@ be nwces~
if c~bration is to be petioned over the ~E4 bus.
4. KiMey Model 4853 EEE48 Intetiace tisti~ed hthe
Model 485.
5. ~85 Computer eqtipped tik ~82937 GP~ kter-
face md 1/0 ROM.
6. KltMey Model 7008 ~E cable.
C~bration shmdd be pefiomed under labrato~ ccm&-
tiom hatig m-bient tempera~ of 23 +l°C md a
relative hufidity of less tha 70%. With both the Model
485 and 263 on, dow them to wam up for one hem. K
either ina~ent has ken subjected to mtieme temper-
atim or hufidity, dow at least one ad~tiond how for
the titiment to stabike before be@tig the ctibra-
tion procedw.
NWE
Cfibration can be stopped at ay tie md ody
those ranges out of spwificatimr need be cd-
bra~d.
Front Panel Calibmtion
Petiom the foE- steps to dbrate the Model& tim
the front pmek .
1. On the Model 485, depress ZERO C~CK and select
the Mrmge.
2. With mopen tiput, adjust the Z~O pot for.~ AI
count on the display.
N~E
HQ104, U105, RIU, Rl14 or RIB hwe been re-
placed, the pico-der may not zero. See paa-
&aph 5.7 hthe Model& btition Manual fur
the pmcedti to bdmce the tiput amp~er.
3. Comect the output of the Model 263 ~hatur/Sowe
to the tiput of the Model 485 as show hFi~ 2.
M*e sue the ctibrator is hstandby.
4. On the Model 485, press the R~ arrd ~G pwh-
buttmrs stidtanemrsly md hold kunti the message
“CAH is &played. Release the buttons. The tit is
now hthe c~bration mode mkdicated by the “~~
annunciator.
5. Release Z~O HCK on the Model 485.
6. Pro&mn the Model 263 to output .m nA. Use the
AMPS (active) -ent some.
7. The Model& maybe displaying asmfl offset (=1
count). TOcmcel this offset, press ML rm the Model
485 to zem the display.
8. Pro~a the Model 263 to output 1.900W nA.
9. Adjust the display of the Model 485 to read l.~
uatig the S~/CLR md RCL httons. The STO/CLR
button hcrements the displayed reading and the R~
button demments the displayed reatig.

MODEL 4W BNC TO TRl~ ADAPTER ~
MODEL 263 MODEL 485
Rgum 2. Model 485 Catibmtion Connections
10. Ustig Table 2as aguide, repeat the basic pmcedme the ~E48 bus ustig the Model 263 C~brator/Sowe.
oufltied hsteps 5thmuxh 9to ctibrate the rest of the
-ent range; of the M;del 485.
11. TOatom A:bration comtmta md ~t the ctibration 1. Comect the Models 263 md 485 to the GP~ titefiace
mode, simti~eously press the ~md LOG buttom of the HP 85 computm. The Model 485 mti have a
UM the message “Stofl is &played. Etitead the Modd &53 ~488 htefiace tistied.
message “ouf’ is displayed, then ctihation storage 2. Make sue the =488 adtiess of the Model 2@ is set
was not embled md cahbatimr crmstits Wbe lost to 8md the adhss of the Model 4853 is set to 22.
when the Model Nis tied off.
Table 2. Model 485 Range Calibtion
263 titput
Cumnt
1.90000 d
19.0000A
190.000 A
Lm &
19.0000@
190.000 @
1.9W d
485 Readtig
IEEE-488 Bus Calibmtion
Pdom the fofltig steps to dbrate the Model 485 mr
3. Enter the c~iration pm~m tito the HP 85 computer.
4. TO‘dbmte the titiment, stiply press the R~ key
on the computi. The -m wfl prompt for the On-
ly marmd adjustimt md then automatically cdbrate
dthe mmnt rmges of the Model 485.
5. The pm-@ prompt for storage of the c~tiation
constita me 330). ~ptides the user the oppor-
tity to stop at this petit to avoid pemment cAha-
tiOn. me Ctibation con~ts WM ~lost when the
Model 485 is tied off.
6. Stomge of c~bmtion comtits is pefimed mrhe 350
of the pmga md is tidcated by the “Stofl message
on the Model 485. Hbtead the message “out” k
displayed, c~iratiorr storage was not enabled md
c~bmtion com~ts w~ be lost when the Model &
is ~ed off,
ZAfter c~bration is completed, it is mcomended that
you somce amnt fmm the Model 263 to each rmge
at kh~ scale bverify acwacy.

10 CLEAR 722 @CLEfiR
22 NAIT 1020
32 OUTPUT 722 ;“CIRIX” !485; set to 2nA range and enable ZERO CHECK.
42 BEEP @DISP ‘AOJUST ‘ZERO’ POT ON 495 FOR .0000 +/-1 COUNT. “
50 DIsP
S0 DISP “IF DISPLAY WILL NOT ZERO, PRO- CEEO TO P6RAGRAPH 5.7 IN THE 48 SMANUAL.
70 OISP
80 DISP ,’PRESS ‘CONT’ KEY ON THE HP 85 TOCONTINUE. “
90 P6USE
100 CLEAR @BEEP
110 DISP “CONNECT ?G3 OIJTPUT TO 485 INPUT (SEE FICURE 2) ~ ~
120 DIS?
130 OISP “PRESS ‘CONT’ TO CONTINUE. “
140 PAUSE
152 06Th 1, .0000000019,2,.000000019,3, .00000019,4, .0000019,5,.000019,6, .00019,7,
160 CLEAR
170 CLEAR 708
180 OUTPUT 708 ;“F1R4UI .gE-gx, !263; program for 1.9nA.
190 OUTPUT 722 ;“COX,, !4S5; disable ZERO CHECK.
200 FOR 1=4 TO 10
210 REAO J
~ZO OUTPUT 722 ~,,R,, ;J; ,,x, !485; ~e~ect ~ange,
230 OUTPUT 708 ;R; I; ,X< !265; select range.
240 OUTPUT 708 ;“Z101X” !263; output zero amp5.
2S0 WAIT 3000
260 OUTPUT 722 ;“ZIXS’ !485; enable REL to cancel Of
270 REAO J@ WAIT 2000
~sO OUTp UT 708 ;,,zOx,, !~E~; source programmed outpu
290 Wfl IT 2000
5et .
300 OUTPUT 722 ;“V’’; J; “X,” !485; send calibration value.
310 OUTPUT 722 ;“ZOX” !485; disable REL.
320 NEXT I
330 BEEP @OISP “TO STORE C6L CONSTANTS, PRESS ‘CONT’ .“
340 PAUSE
350 OUTPUT 722 ;‘“LOX,’ !485; store cal constants.
560 CLEhR @BEEP
370 DISP “CfiLIBRATION COMPLETE”
380 END
485 CALIBRATION PROGRAM

MODEL 485 AUTORANGING PICOAMMETER
Features:
l 4% Digit LCD Display
l Fast Autoranging
l Bench or Portable
l Digital Calibration
l 100 Point Data Store
l O.lpA Sensitivity
l Analog Output
l LOG/Relative Functions
l Min/Max Reading Hold
Options:
l Model 1758 Rechargeable Battery Pack
l Model 4853 IEEE-488 Interface
vi

SECTION 1
GENERAL INFORMATION
1.1 INTRODUCTION
This instruction manual contains the necessary information
for operating and maintaining the Model 485 Autoranging
Picoammeter and the Model 1758 Rechargeable Battery
Pack. The information is divided into the following sections:
1. Section 1 contains general information and provides
guidelines for using this manual. Important safety infor-
mation is also presented here.
2. Section 2 contains detailed operation information for the
Model 485.
3. Section 3 contains the information needed to verify the
accuracy of the Model 485. Performance verification can
be done upon receipt of the unit or whenever the basic ac-
curacy is in question.
4. For the more technically oriented, information on theory
of operation, maintenance and servicing is contained in
Section 4 through 6.
NOTE
The Model 4853 IEEE-488 interface comes sup-
plied with its own instruction manual.
1.2 GElTlNG STARTED
Perform the following steps in sequence to acquaint yourself
quickly and safely with the basic operation of the Model 485.
1.
2.
3.
4.
Verify that the Model 485 was not damaged in transit, as
explained in paragraph 1.3.
Carefully read the safety precautions and warnings found
preceding this section and the first two sections (General
Information and Bench Operation) of this manual.
Referring to paragraph 2.2.1 (Line Power) set the line
voltage switch and plug the power cord into a properly
grounded cutlet. If the optional battery pack is installed
the charge circuitry will be activated.
Acquaint yourself with the controls and display of the
Model 485 as follows:
A. Turn on the Model 485 by pressing in the ON/OFF
pushbutton. All the zeroes will be displayed briefly.
B. Select autoranging by pressing in the AUTO pushbut-
ton. The nA and AUTO annunciators will be displayed.
Pressing any of the other range pushbuttons will put
the Model 485 in manual ranging as indicated by the
absence of the AUTO annunicator.
C. Engage the ZERO CHECK pushbutton and note that
the ZERO CHECK annunciator turns on. Release the
ZERO CHECK button.
D. Select LOG by pressing the LOG pushbutton. The
LOG annunciator will turn on. Press the LOG button
again to take the Model 485 cut of the LOG measure-
ment mode.
E. REL (relative) can be used in the linear measurement
mode or the logarithm measurement mode. The
stored REL level will be subtracted from all subsequent
measurements. Press the REL pushbutton and note
that the REL annunciator turns on.
F. To activate the 100 point DATA STORE with
MinIMax, press end hold in the STO/CLR pushbut-
ton. When the reading rate r = 0 is displayed let go of
the button. The ST0 annunciator will turn on. Press
the RCL pushbutton and the last data point will be
displayed briefly followed by the reading (data). Other
date points can be displayed by holding in the RCL
button. Turn off the DATA STORE by pressing the
STO/CLR pushbutton again.
5. When you are comfortable with the controls of the Model
485, go on and make the desired measurements using
Section 2, Bench Operation as a guide.
1.3 INSPECTION
The Model 485 Bench Picoammeter was carefully inspected,
both mechanically and electrically, before shipment. Upon
receiving the Model 485, check for any obvious signs of
physical damage that might have occurred during shipment.
Report the damage to the shipping agent immediately. Retain
the original packing materials in case reshipment becomes
necessary. The following items are included with every Model
485 order:
l Model 485 Autoranging Picoammeter
l Model 485 Instruction Manual
l Additional accessories as ordered.
If an additional instruction manual is required, order then
manual package (Keithley Part Number 486-901-00). The
manual package includes an instruction manual and all perti-
nent addenda.
1.4 SPECIFICATIONS
Detailed Model 485 specifications may be found immediately
preceding the table of contents of this manual.
1.5 WARRANTY INFORMATION
Warranty information may be found on the inside back cover
of this manual. Should it be necessary to exercise the warran-
ty, contact your Keithley representative or the factory to
determine the correct course of action. Keithley Instruments
maintains service facilities in the United States, West Ger-
many, Great Britain, France, the Netherlands, Switzerland
1-l

and Austria. Information concerning the application, cpera-
ticn or service of your instrument may be directed fc the ap-
plications engineer at any of these locations. Check the inside
front cover of this manual for addresses.
1.6 MANUAL ADDENDA
Information concerning improvements or changes to the in-
strument which occur after the printing of this manual will be
found on an addendum sheet included with this manual. Be
sure to review these changes before attempting to operate or
service the instrument.
1.7 SAFETY SYMBOLS AND TERMS
The following safety symbols and terms are used in this
manual or found on the Model 485.
The symbol A on the instrument indicates that the user
should refer to the operating instructions in this manual.
The WARNING heading in this manuel explains dangers that
could result in personal injury or death.
The CAUTION heading in this manual explains hazards that
could damage the instrument.
1.8 OPTIONAL ACCESSORIES
The following accessories can be used with the Model 485.
Model 1010 Single Reck Mounting Kit-Use to mount
one Model 485 in e standard 5% x 19” rack.
Model 1017 Dual Reck Mounting Kit-Use to mount two
Model 486’s in a standard 5% x 18” rack.
Model 1684 Hard Shell Carrying Case-Hard vinyl case,
IOOmm x 300mm x 350mm (4 x 13 x 14 inches) has a fit-
ted foam insert with room for the Model 485, instruction
manual end small accessories.
Model 1768 Rechargaable Battery Pack-Provides six
hours minimum operation from full charge, recharges within
10 hours end is field installable.
Model 4801 Input Cable-A low noise coaxial cable four
feet (1.2m) in length with a male BNC connector on each
end.
Model 4803 Low Noise Cable Kit-Consists of 50 feet
(15.2m) of low noise coaxial cable, 10 male BNC connectors,
and five female chassis mount BNC connectors.
Model 4863 IEEE-486 Interface-Field installable prcgram-
mable option provides isolated data output. Switch-
selectable talk only or addressable modes. Mounts within and
powered by the Model 485.
Model 7008 IEEE-488 Digital Cable-Useful for ccnnect-
ing the Model 4853 to the IEEE-488 bus. The Model 7008-3 is
0.9m 13ft) in length and has a standard IEEE-488 connector
at each end. The Model 7008-6 is 1.8m (6 ft) in length.
Modal 8673 IEEE-486 Interface for IBM PC-Field in-
stallable programmable option provides data output for the
IBM PC. Mounts within and powered by the IBM PC.
l-2

SECTION 2
BENCH OPERATION
2.1 INTRODUCTION
This section contains the information needed to prepare and
operate the Model 485 as a bench picoammeter. Bench
operation consists of using the Model 485 to perform basic
current measurements. Data store operation is also covered.
The capabilities of the Model 485 can be enhanced with the
addition of the Model 4853 IEEE-488 interface. IEEE opers-
tion is covered in the Model 4853 Instruction Manual.
2.2 PREPARATION FOR USE
2.2.1 Line Power
The Model 485 is provided with a three-wire line cord which
mates with third-wire grounded receptacles. Connect the in-
strument to AC line power as follows:
1. Set the LINE VOLTAGE switch on the back of the instru-
ment to correspond to line voltage available. Ranges are
105-125V or 210-250V 50/60Hz AC.
CAUTION
Connect only to the line voltage selected.
Application of incorrect voltage can
damage the instrument.
2. Plug the power cord into a properly grounded outlet.
WARNING
Ground the instrument through a properly
grounded receptacle before operation.
Failure to ground the instrument can result
in severe injury or death in the event of
short circuit or malfunction.
NOTE
Although the Model 485 is specified at 50Hz and
60Hz the instrument may be operated at 400Hz
and 440Hz. Add one count to instrument
specifications under this condition.
2.2.2 Battery Pack Power
The Model 485 may also be operated from rechargeable
sealed nickel-cadmium batteries contained in the optional
Model 1758 Rechargeable Battery Pack. The battery pack will
operate the Model 485 for up to six hours. The BAT ennun-
ciator will turn on when the banely charge is insufficient to
maintain eccurate readings. Refer to Section 5, paragraph 5.3
for installation procedures.
2.2.3 Battery Charging
After the Model 1758 Banery Pack is installed in the Model
485 it can be charged and recharged as follows:
1. Connect the instrument to line power as described in
paragraph 2.2.1.
2. With the power switch off, the battery charge circuitry is
automatically energized to charge the battery at the maxi-
mum rate. When the battery pack is first installed, or if it is
completely discharged, allow it to charge for ten hours.
NOTE
For maximum battery efficiency only charge the
battery pack after it has become discharged and
only charge until it is fully charged I,10 hours).
Continuous charging over long periods of time
will not damage the batteries but, useful life will
gradually decrease. This loss is not permanent
and may be restored by cycling the battery pack
through several complete charge/discharge
cycles. The battery pack is capable of 500 to
1000 charge/discharge cycles before replace-
ment is needed.
Do not make measurements with the BAT annunciator on as
the readings may be erroneous.
3. When the Model 485 is in use on line power, the banely
charger maintains a trickle charge on the battery pack.
2.3 TILT BAIL
The Model 485 is equipped with a tilt bail which makes it
possible to elevate the instrument to a convenient viewing
position. To change the bail position, pull out the bail handle
from each side of the case until it rotates freely; rotate the bail
to the desired position and release the bail to allow it to lock
into place.
2.4 MODEL 485 FAMILIARIZATION
The following paragraphs and Figure 2-l provides a brief
description of the display, front panel controls and connec-
tors.
2.4.1 Display
The Model 485 has a 4% digit liquid crystal display (LCD).
The minus sign is displayed. The plus sign is implied by the
absence of the minus sign. The following annunciators are
displayed on the LCD.
2-l

BAT-Low battery indicator for the Model 1758.
nA. uA or mA-Nanoamos. Microamos or Milliamos
selected.
RMT IRemote)-Model 485 being controlled over the
IEEE-488 bus (Model 4853 installed).
CAL-Model 485 in calibration mode.
AUTO-Autorange selected.
REL-Relative selected.
LOG-Logarithm selected.
ZERO CHECK-Zero Check selected.
BTO- Data being stored.
RCL-Data being recalled. RCL flashes when buffer is full
during store cycle.
2.4.2 Front Panel Controls
ON/OFF-Pressing in this pushbutton turns the Model 485
on. Releasing (out) this pushbutton turns the instrument off.
ZERO CHECK and ZERO-This pushbutton and trimpot are
used to zero the instrument’s internal offsets.
REL (Relative)-This pushbutton is used to cancel measure-
ment offsets or store the input signal as a reference level.
Pressing this button again shuts REL off.
LOG-This pushbutton selects the logarithm function. The
displayed current measurement is expressed as the logarithm
(base IO) of the measured current referenced to one ampere.
Pressing this button again shuts LOG off.
DATA STORE-Has MlNlMAX and 100 point reading
storage capachY; records data at one of seven selectable
rates. Records minimum and maximum conversion during
the period the data store is active at the rate of 3/set.
1. STO/CLR-Pressing this button initiates the storage se-
quence. Pressing the button a second time shuts off the
data store when in r=Othrough r=5. When in r=6, press-
ing this button stores one reading.
2. RCL-Pressing and holding this button in scrolls the data
pointer. To read the data at a particular point, simply
release the button.
Range Pushbuttons
1. Auto-This pushbutton selects autoranging.
2. Manual ranging is accomplished by depressing the ap-
propriate range button.
2.4.3 Input Connector
The input connector is a standard BNC type.
2.4.4 Analog Output Connectors
A voltage level that is proportional to the incoming current
can be monitored using the analog output banana jacks
located on the rear panel.
2.5 ERROR MESSAGES
Table 2-1 lists the error messages associated with basic front
panel operation. Note that the instrument has a number of
other messages that are discussed in the appropriate sections
of this manual.
i_J
ITHLEY 485 AUTORANGING PICOAMMETER 4 \
Figure 2-l. Model 485 Front Panel
2-2