Fluke 8508A, Service Manual

Page: 64 / 120

8508A
Service Manual
3-24
For the 2 G
Ω
range use the 1 G
Ω
standard resistor in place of the calibrator. To avoid the
requirement for a 10 G
Ω
standard, the 20 G
Ω
range is automatically calibrated when the
2 G
Ω
range gain calibration is triggered. It is also necessary for the 100 M
Ω
and 1 G
Ω
Normal
Ω
ranges to be calibrated prior to the 2 G
Ω
HiV
Ω
range for the result to be valid.
A 10 G
Ω
standard resistor may be used for calibrating the 20 G
Ω
range if available, but
if performed, this operation must take place after the 2 G
Ω
range gain point calibration to
avoid the automatic process overwriting the result.
Voltages of approximately 200V will be developed across the resistance standard at full
scale, ensure the resistance standards used are suitable for operation at these voltages.
Note that EX SNS (4-wire) is not available on the 5720A 100 M
Ω
range, and the 8508-
7000K 1 G
Ω
standard resistor is used as a 2-wire device with the calibrator 2-wire
resistance zero used for the corresponding zero points.
4W
Ω is deselected on the
Multimeter when calibrating the 200 M
Ω
and 2 G
Ω
range, range zero, and range gain
points.
On each range, the Multimeter automatically recognizes the appropriate value as range
zero or range gain from the applied resistance value.
Note
It is unlikely that the resistance standard will be at exactly the nominal
value required. The Set feature allows a user to enter the true output value
of the calibration standard where it differs from nominal range gain point.
If the resistance value is exactly the nominal value required, omit steps 2-4
for the Range Gain Point .
Zero Point
1. On the Multimeter, select the required range.
2. On the Calibrator, select zero
Ω
and Operate. (For the 200 M
Ω
range and above, de-
select Ex SNS on the calibrator and de-select
4W
Ω
ο
n the Multimeter.) Alternatively
if using a standard resistor connect the standard resistor for a 4-wire resistance zero.
3. On the Multimeter, press
CAL
to enter the
CALIBRATION
menu.
4. Press
SAMPLE
to initiate the calibration operation.
Calibration is complete when the Busy legend goes out and the calibrated
measurement is displayed.
Range Gain Point
1. On the Calibrator, select Range Gain point Output value. Alternatively if using a
standard resistor re-connect the standard resistor to measure its resistance. (For the
2 G
Ω
range the 8508-7000K 1 G
Ω
standard resistor is used in place of the calibrator.
For the 200 M
Ω
range and above, de-select Ex SNS on the calibrator and de-select
4W
Ω
ο
n the Multimeter. Calibration of the 20 G
Ω
range gain point takes place
automatically when calibrating 2 G
Ω
range, and calibration against an external
standard is optional if a suitable standard is available).
2. On the Multimeter, Press
CAL
to revert to
CALIBRATION
menu.
3. Select
Set
on the
CALIBRATION menu
.
4. Use the numeric keys with the
SET VALUE
menu to key in the true output value of
the calibrator (or the value of the resistance standard) at the range gain value, then
press Enter.