Keithley 485 User Manual
MODEL 485
AUTORANGING PICOAMMETER
QUICK REFERENCE GUIDE
INTRODUCTION
This reference and programming guide contains condensed specifications and information which describes the various features of the
Model 485. Each feature is described in three segments of information. The first segment describes the features. The second segment
gives an exact procedure on how to use the feature. The third segment 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 Instruction Manual for complete information and essential safety information.
With the Model 4853 IEEE-488 interface installed, the Model 485 can
be controlled over the IEEE-488 bus. This booklet also contains information concerning Model 485 bus operation. Several example programs using some commonly used controllers are outlined to get the
Model 485/4853 “up and running”.
CONTENTS
CONDENSED SPECIFICATIONS ..........................
MODEL485 FEATURES
IEEE-488 PROGRAMMING..
PROGRAMS
IBM-PCorXTPersonalComputer..
(Keithley Model 8573 Interface)
APPLE II (Apple Interface)
HP-85 .................................................
HP-9825A.. ...........................................
HP-9816 ...............................................
HP-9845B.. ...........................................
TEK4052 ..............................................
DECLSIll..
PETlCBM2001
EH 7000 Computer
............................................
................................... 5
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....................... 19
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01984. Keithley Instruments, Inc.
Cleveland, Ohio, U.S.A.
Document Number: 485903-OlA
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CONDENSED SPECIFICATIONS
Accuracy (1 year)
18O -2WC
Range
2OilnA
INPUT VOLTAGE BURDEN: Less than 2OOhV.
RANGING: Manual or autoranging.
AUTORANGING TIME: 2COms per range.
SElTLING TIME AT DISPLAY: Less than lsec to within 1 cuunt after
CONVERSION PERIOD: 300ms.
TEMPERATURE COEFFICIENT: -z f0.1 x applicable accuracy
MAXIMUM COMMON MODE VOLTAGE: BOVrms, DC to 60Hz
ANALOG OUTPUT:
RELATIVE: Pushbutton allows zeroing of on range readings. Allows
DATA STORE and MINIMAX: 100 reading storage capacity. Records
LOG: Displays the logarithm (base 10) of the input current referenced to
Resolution
2nA
20 nA
W&h no limitiw resistance: 1OOOVdc with external lOOk series resistance.
ranging.
specification per T.
sine wave.
Output Voltage: +lV, = -10000 counts. (Except +lOOmV =
-1OoM) wunts on 2nA range.)
Output Resistance: 1OOOQ.
readings to be made with respect to baseline value. Front panel
annunciator indicates REL mode.
date at one of seven selectable rates from Brdgs/s to lrdg/hr and
manual triggering. Also detects and stores maximum and minimum
readings continuously while in the data store mode.
1A.
O.lpA
1 PA
10 pA
100 nA
1llA
10 nA
100 nA
*(%rdg + countsIt InputS
0.4 + 4 35OVdc
0.4 -t 1 35OVdc
0.2 + 1 35OVdc
0.15 + 1 35OVdc
0.1 +1
0.1 +1 5OVdc
0.1 +1 5OVdc
Maximum
Continuous
5OVdc
J
1
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SAFETY SYMBOLS AND TERMS
I
The ayrnboj
the operating section in the Model 455 Instruction Manual.
The WARNING used in this guide explains dangers that could result in
personal injury or death.
on the instrument denotes that user should refer to
Q
SAFETY PRECAUTIONS
1. Before operation, ground the instrument through a properly earth
grounded power receptacle.
2. Before servicing, disconnect the instrument from the power line, all
other equipment and consult the Model 455 Instruction Manual.
3. Do not touch the input terminal while the instrument is turned on or
connacted to any other tast equipment. Common mode voltage may
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 relative mode isselecttxl. The reading is r&t&
to some previous reading.
LOG-Log mode reading is directly in log (base 101.
SO-Indicates that the data store and minimax hold function is running. Displayed raadjng is present input.
RCL-Indicates that the displayed reading is recalled data.
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 impedance changes when in the zero check mode.
nA, & or mA-Nanoamps, microamps or milliamps selected. Read
measurement directly from the display. (e.g. 1.2345fll
RMT--(Remote) Model 485 is being controlled over the IEEE-488 bus
(Model 4853 installed).
CAL-Indicates that the Model 435 is in the calibration mode.
4
MODEL 485 FEATURES
RANGE t2nA to 2mAl
35ov
5ov
I z&v I
Description
The range buttons se&t the desired range of current measurement for
the Model 485. The range may’ be selected manually or automatically.
With manual range selection always use the range that allows the
greatest amount of resolution.
Operation
Manual
1. Determine signal to be measured.
2. Press appmpriate range button.
3. Apply signal.
Auto
1. Press the AUTO button.
2. Apply signal.
MAX
MAX
5ov 5ov
MAX MAX
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ZERO CHECK
DesctiptIon
The ZERO CHECK button is used to correct interna ofFsets and also
protects the sensitive input circuitry from build up during overloads. In
the zero check mode or input overload, the input impedance of the
Modal 495 is changed as outlined in the following table.
INPUT RESISTANCE WITH ZERO CHECK ENABLED
Current Maximum Effective
Ranae lmut Resistance
2nA 1
1. Select range.
2. Depress ZEFtO CHECK. The ZERO CHECK button operatas on the
push-push principle. That is, pressing in the button locks the instrument in zero check, pressing the button again releases the zero check
mode.
Typical Use
Used in zeroing the 2nA range for precise measurements. Refer to
paragraph 2.72 in the Model 495 Instruction Manual.
1GMl
6
Impedance In
Zero Check/Overload
9MWX3IpF
REL (Relative Function)
REL
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Description
The relative function serves as a means of baseline suppression allowing
a stored offset value to be subtracted from subsequent readings. When
the REL button is pressed, the instrument stores the baseline reading
with the next conversion. All subsequent readings represent the di-
ferences between the applied signal level and the stored baseline. The
stored baseline can be as small as the resolution of the instrument will
allow or as large as full range.
It is important to note that the REL function reduces the dynamic range
of measurements by that level (stored baseline). For example: assume
that the REL level is + Id and the Model 495 is manually set to the w
range. The maximum positive displayed reading, before overranging,
would be + 0.9999& This is because the A/D converter would 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 dynamic range can be
reduced by selecting e higher range or using autorange.
Operation
1. Select measurement mode and range. For example: normal measurement mode and the w range.
2. Press REL. The display reads zero.
3. The value that appeared on the display is now the stored offset.
Typical Use
1. Nulling out external source offset (e.g. calibrator offset).
2. Nulling out desired levels of offset (e.g. electrode dark current of
phototube).
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LOG (Log Function)
Description
The log function gives the log (base 101 of the measured input current
referenced to 1A. Log can be used to make any current level the 0.0
(zero) point for log measurements. This can be done by selecting
autorange and log. Then measuring the desired current that is to 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
displayed as e log. Press the REL button and the display wiil 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:
Display = Log -
Operation (referenced to IA)
1. Select the auto range mode.
2 Apply the source.
3. Press the LOG button. The LOG annunciator on the display turns on.
4. Take the log reading from the display.
Typical Use
1. For use in measuring e wide range of current. Nuclear reactors have
various outputs of current that could be compressed (in readings only) by using the log function.
2 Measuring the current output of a phototube. REL can be used to
nu[l the dark current of the phototube.
Input
1 Amp
I I
DATA STORE (100 Point Data Store1
Description
The 100 point data store function serves to save up to 100 points of 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 useful in applications where data is required to be
logged over a period of time.
Operation
1. Connect desired measurement configuration to the Model 485.
2. Select rate of storage and begin data store:
A. Press and hold in the STO/CLR button.
6. The rates are scrolled on the display. Tithe rates are described
below).
C. Release the STWCLR button when the desired rate is displayed.
D. The ST0 annunciator turns on indicating that the data is being
stored at the selected rate.
Typical Use
1. Saving data points of current drift of a low leakage device such as e
FEr.
2. Monitoring and saving current levels that 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 reading per minute)
r = 4 I1 reading per 10 minutes)
r = 5 (1 reading per hour)
T = S (every time STOKLR is pressed)
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