Keithley 486 User manual

Model 486
PICOAMMETER
Model 487
PlCOAMMETER/SOURCE
QUICK REFERENCE GUIDE

INTRODUCTION
This quick reference guide contains descriptions of vari-
ous features and information concerning the operation of
the Model 4861487.
~21990,Keithley Instruments, Inc.
All rights reserved.
Cleveland, Ohio, U.S.A.
Document Number: 486-903-01 Rev. A
1

Asyst tsa registered trademarkof Asyst Software technologies.
Hewtett-Packard Is a registered trademark of Hewlett-Packard
Company.
IBM and ATare registeredtrademarksand PC/XTisatrademark
of International Business Machines, I~C.
PC&488 isa registered trademark of Capital Equipment Cow
ration.
2

TABLE OF CONTENTS
SAFETY WARNINGS ......................... 5
ERROR MESSAGES ......................... 7
CURRENT MEASUREMENTS .................. 8
VOLTAGE SOURCE (Model 487) .............. 14
V/l OHMS MEASUREMENTS (Model 487) ....... 19
MENU .................................... 21
FRONT PANEL TRIGGERING ................. 22
EXTERNAL TRIGGERING .................... 24
DATA STORE OPERATION .................. 26
ANALOG OUTPUT .......................... 27
TALK-ONLY ............................... 28
IEEE-488 PROGRAMMING .................. .29
Device-dependent Commands ................. 29
Display Intensity ........................ 29
Reading Source ........................ 29
Zero Check and Correct .................. 29
Display ............................. ..3 0
V/lOhms ........................... ..3 0
Data Format ........................... 39
Hit Control ............................ 31
Self-Test .............................. 31
EOI and Bus Hold-off ................... .31
Default Conditions or Calibration ........... 32
SRQ ............................... ..3 2
Data Store ............................ 32
Operate .............................. 33
Filters ................................ 33
Interval ............................... 33
Range................................3 3
Integration ............................ 34
3

Trigger ...............................
Status.. ..............................
Voltage Source (487)
i:l
.................... 35
Delay ................................
Execute ............................ 35 a
..3 5
Terminator .......................... ..3 5
Relative .............................. 36
Data Formats .............................. 36 a
SRQ Mask and Serial Poll Byte ................ 40
StatusWords ............................ ..4 1 a
4

SAFETY WARNINGS
The following precautions should be observed before us-
ing Model 488/487. Refer to main manual for detailed
safety information and complete operating instructions.
The Model 48W487 is intended for use by qualified per-
sonnel who recognize shock hazards and are familiar
with the safety precautions required to avoid possible in-
jury. Read over the instruction manual carefully before
using the instrument.
Before operating the instrument, make sure the line cord
is connected to a properly grounded power receptacle.
Exercise extreme caution when a shock hazard is pre-
sent. Lethal voltages may be present on the test fixture or
the Model 487 output jacks. The American National Stan-
dards Institute (ANSI) states that a shock hazard exists
when voltage levels greater than 30V RMSor 42.4V peak
are present. A good safety practice is to expect that
hazardous voltage is present in any unknown circuit
before measuring.
Inspect the connecting cables, test leads, and jumpers
for possible wear, cracks, or breaks before each use.
5

For maximum safety, do not touch the Model 487 con-
nections, test fixture, test cables or connections to any
other instruments while power isapplied to the circuit un-
der test. Turn off all power and discharge all capacitors
before connecting or disconnecting cables or jumpers.
Also, keep the test fixture lid closed while power is ap-
plied to the device under test. Safe operation requires the
use of the lid interlock.
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.
Do not exceed the maximum signal levels of the instru-
ment, as shown on the rear panel and as defined in the
specifications and operation section of the instruction
manual.
Connect the chassis of the test fixture to safety earth
ground using #I 8 AWG or larger wire.
Instrumentation and accessories should not be con-
nected to humans.
Maintenance should only be performed by qualified serv-
ice personnel. Before performing any maintenance, dis-
connect the line cord and all test cables from the instru-
ment.
6

ERROR MESSAGES
Table 1. Error Messages
Message Description
NO DEFLTS Checksum error in default condi-
tion during power-up.
UNCAL Checksum error in calibration
during power-up
ROM ERROR Failed ROM self-test.
RAM ERROR Failed RAM self-test.
TRG OVERUN Trigger overrun; instrument trig-
gered while still processing a pre-
vious trigger.
CAL VALUE Calibration value conflicts with
the currently selected range.
CAL ERROR Calibration value not within allow-
able limits.
CAL LOCK Sent calibration command with
calibration switch (CAL LOCK)
disabled.
CAL ZCHK Cannot calibrate picoammeter
with zero check enabled.
INTERLOCK Tried to put V-Source of Model
487 in operate while an enabled
safety interlock switch is open.

CURRENT MEASUREMENTS
Current Ranges
SHIFT
q v RANGE A
El 0
AUTO
RANGE
The available current ranges of the Model 4861487 are
listed in Table 2.
2nA
20nA
200nA
2c1A
20/.iA
2oopA
2mA 2.19999inA
‘Higher voltages requirecurrent to be limitedto 3mA.
2.19999nA
21.9999nA
219.999nA
2.19999pA
21.9999pA
219.999uA
35OVdc
35OVdc
35OVdc
35OVdc
5OVdc
50Vdc
50Vdc
Table 2. Current Ranges
.

Autorange is enabled by pressing SHIFTand thenAUTO
RANGE in that order.
CAUTION
To avoid possible damage to the instru-
ment, do not apply more than 5OVdcto
the input when autorange is enabled
(unless an external series resistor to
limit current to 3mA is used).
Zero Check and Correct
ZERO
SHIFT CHECK
q El
CORRECT
When zero check is enabled, the input amplifier is inter-
nally disconnected from the input connector of the instru-
ment. A 1OOkGresistor shunts the input connector, and
the instrument displays the offset of the selected range.
When zero correction is performed, the offset is meas-
ured and algebraically subtracted from every subsequent
reading (including zero checked readings).
Zero check is enabled by pressing ZERO CHECK.
Pressing ZERO CHECK a second time disables the fea-
ture.
9

When zero correction is performed, only the present
range iszero corrected. Before making measurements, it
is recommended that each current range be zero cor-
rected.
To perform zero correction:
1. Enable zero check.
2. To perform zero correction, press SHIFT and then
CORRECT in that order.
Filters
SHIFT
cl
Filtering is used to stabilize noisy measurements. The
Model 486/487 has two available filters; a digital filter and
an analog filter. The digital filter bases the reading on the
weighted average of a number of measurement conver-
sions. The analog filter is a simple RC filter whose time
constant varies with the selected range.
When the filter is enabled, the selected filter(s) (digital fil-
ter, analog filter or both) will be used.
10

To check or change the filter selection:
Press SHIFT and then FILTER SELECT in that or-
der. One of the following messages will be dis-
played to indicate the currently selected filter(s):
FILTER DIGITAL
FILTER ANALOG
FILTER DIG+AN
(Digital filter selected)
(Analog filter selected)
(Both digital and analog
filters selected)
To select a different filter, use the rotary knob or the
4 and b keys to display the desired filter selection.
Enter the displayed filter selection by pressing
SHIFT and then FILTER SELECT.
Rel
REL
q
0
The rel (relative) feature serves as a means of baseline
suppression by allowing a stored offset value to be sub-
tracted from subsequent readings. When rel is enabled,
the instrument takes the currently displayed reading as a
baseline value. All subsequent readings represent the
difference between the applied signal level and the
stored baseline.
11

A baseline can be established for both current and VII
ohm measurements and is “remembered” by both func-
tions.
Rel is enabled by pressing the REL key. Pressing REL a
second time disables the feature.
Making Current Measurements
To make current measurements:
1. Select a current range that isappropriate for the ex-
pected measurement or enable autorange (press
SHIFT and then AUTO RANGE).
2. Enable zero check and, ifthe display is not zeroed,
perform zero correction by pressing SHIFT and
then CORRECT.
3. Connect the current to be measured to the input of
the Model 486/487 (see Figures 1 and 2).
4. Disable zero check and read the measured current
on the display of the Model 486/487.
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Input Connector
Max Overload
2nA - 2pA Range; 35OVdc
2OpA- 2mA Range; 50 Vdc
Chassis Gmund
Fiaure 1. Triax InDut Connector (3-Lua)
Figure 2. Picoammeter Connections
Model486

VOLTAGE SOURCE
(Model 487)
CAUTION
The voltage source may float. However,
neither V-Source terminal may ever be
more than 500V above chassis.
V-SOURCE OUTPUT
500V MAX TO ,& OR.+
I HI LO 1
5oov
MAX
Figure 3. Model 487 V-Source Output Terminals
Table 3. Model 487 V-Source
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Test Fixture and Interlock
The voltage source of the Model 487 is designed to be
used with atest fixture that incorporates a safety interlock
switch, such as the Keithley Models 8002A High Resis-
tance Test Fixture. By using the interlock feature, the
Model 487 cannot source voltage when the lid of the test
fixture is open or ajar.
Adjusting V-Source Level
The rotary knob and the4 and, keys are used to adjust
the V-Source level and select range.
WARNING
With the instrument in operate (OPER-
ATE indicator on), the displayed voltage
level (possibly hazardous) will be ap
plied to the output terminals of the V-
Source. The V-Source should be kept in
standby until ready to safely source
voltage to a load.
15

Preset
PRESET
Preset allows the V-Source to be toggled between two
preset values.
To preset a V-Source level:
1.
2.
3.
4.
Enable preset by pressing PRESET. Indicator wljl
turn on.
Adjust the V-Source to the desired range and level.
Disable preset by again pressing PRESET.
Whenever preset is enabled, V-Source will adjust
to the value and range set in step 2.
I-Limit
The V-Source has current limit (l-limit) capabilities to pro-
tect the instrument and external current sensitive circuitry
from possible damage. The V-Source can be set for an
l-limit of 25pA or 2.5mA.
When l-limit occurs, the OPERATE indicator will flash.
16

To set l-limit:
1. Keep pressing and releasing MENU until the cur-
rently selected i-limit is displayed:
ILIMIT
or
ILIMIT
251rA
2.5mA
2. Use the rotary knob to display the desired l-limit
value.
3. to enter the displayed l-limit, press MENU.
Operate
5oov 2mA
MAX
OPERATE
III
0
FLASHES
IN I LIMIT
The OPERATE key toggles the output between standby
and operate. In standby, the V-Source is removed from
the rear panel output terminals. In operate, V-Source is
applied to the output terminals.
17

V-Source Operation
1. While in standby, connect the V-Source as shown
in Figure 4.
2. Use the rotary knob, and the 4 and b keys to set
the desired voltage range and level.
3. Select the appropriate l-limit (25pA or 2.5mA).
4. Press Operate.
5. To disable the V-Source, again press OPERATE.
3anana r;
‘lug Cables
HI r -- 7
-%---I Safety
1 Shield
Model 487
Figure 4. Basic V-Source Connections
18

V/I OHMS MEASUREMENTS
(Model 487)
By using the V-Source in conjunction with its picoamme-
ter, the Model 487 can make resistance measurements
as high as 5.05 x 10i6fI. With V/I ohms selected, the re-
sistance is automatically calculated from the applied volt-
age and measured current (R=V/I) and displayed (in
ohms) on the Model 487.
The V/I ohms function is enabled by pressing SHIFT and
then OHMS.
To make VA ohms measurements:
1.
2.
3.
4.
5.
6.
7.
8.
With zero check enabled and the V-Source in
standby, connect the circuit shown in Figure 5.
Select a current range that gives the nearest full
scale reading or autorange, and perform zero cor-
rection by pressing SHIFT and then CORRECT.
Set the V-Source to OVon Ihe range that will be
used and press OPERATE to enable the source
output.
Press REL to cancel offset current.
Set the V-Source to the desired voltage level.
Disable zero check. The current measurement will
be displayed.
Enable V/I ohms by pressing SHIFT and then
OHMS.
To measure from a baseline resistance, enable ref
while in V/I ohms.
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