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