Keithley 486 Instruction Manual page 165

SECTION 7
Maintenance
10.
11.
If&Model 197isnotreading+50.000V,repeatsteps
5 throueh 9. Otherwise. uroceed to the next steo.
Settheii-Sourcetoout+OOO.OOV ontheSOOV&nge
by sending the following command over the bus:
vo, 1x
12. Send the following command over the bus to pre-
pare the 500V range for calibration:
L6X
13. Adjust the V-Source output of the Model 487 to
m-e (as close as possible) OO.OOOmV on the
Model 197.
14. Send the following command over the bus to cali-
brate OV on the 500V range:
15. Adjust the V-Source output of the Model 487 to
measure +5OO.OOV on the Model 197.
NOTE
If the output cannot be adjusted high enough
to measure 5OO.OOV on the Model 197, set the
V-Source to its maximum output setting
(505.OOV displayed on the Model 487).
16. Send the following command to calibrate the 500V
range at full scale:
WX
17. IftheModel197isnotreading+500.OOV,repeatsteps
12 through 16.
18. Place the V-Source of the Model 487 in standby.
L5X
Calibration Errors
CAL ERROR - The message "CAL ERROR" indicates
that the calibration Constants calculated by the instzu-
ment during the calibration procedure are not within ac-
ceptable limits. This may be due to a calibration source
value which is outside allowable limits, or hardware er-
rors in the instrument which are too great to be compen-
sated by digital calibration. Ail current calibration source
values must be 190000 counts B500 counts. In the event
of this error, the calibration constants are not changed
from their previous values. To clear the displayed error
message, press any front panel key. If this error persists
when using valid calibration values, then service will be
necessary.
CAL VALUE - The briefly displayed message "CAL
VALUE" indicates that the calibration value conflicts
with the currently selected range. For example, sending a
cd value of 19Op.A on the20@ range will cause this error
to occur. In the event of this error, calibration wiIl not be
performed.
CAL LOCK - This message indicates that the calibra-
tion switch (CAL LOCK) is in the disabled position. Cali-
bration will not occur.
It is important to realize that if any of these errors occur,
calibration does not occur. When a calibration error oc-
curs, find and fix the problem and repeat calibration.
It is strongly recommended that calibration errors be de-
tected and displayed by the calibration program. The fol-
lowing steps provide the general procedure required to
detect calibration errors over the IEEE-488 bus:
1. Program the Model 486/487 to generate an SRQ on
anerrorbysendingtheU32cmnman doverthebus.
2. When an SRQ OCCUB (error), send the Ul command
and then address the Model 486/487 to talk.
3. Display the character string (LJl Error Status Word)
from the Model 486/487on the Computer~CRT and
refertoFigure4-7(iiSection4) todeterminethetype
of error.
7.4 HANDLING AND CLEANING
PRECAUTIONS
When froubleshootig or otherwise working inside the
instrument, care should be taken not to indisaiminateIy
touch PC board traces and open wires to avoid contami-
nating them with body oils or other foreign matter. Areas
covered by the shield within the Model 486/487 have
high impedance devices or sensitive circuitry where con-
tamination could cause degraded performance.
The same general precautions apply when replacing
parts in these areas. When unsoldering and soldering
parts, be careful not to spread the flux around the board
to adjacent areas.
1. Using a squeeze bottle, carefully apply clean, uncon-
taminated methanol to the area to be cleaned. Use
7-8