Adjustment and Verification
Non-volatile input offset compensation
6
Non-volatile input offset compensation
Good metrology practice should ensure that all high-precision measurements made with
the 8508A are preceded by an input zero of each measurement. However, a non-volatile
input-offset compensation is independently available for the front and rear inputs. This
compensation is retained after power down and is unaffected by clearing the volatile
input zeros. It is cleared by performing range zero adjustments. Compensation is
available on all functions, and includes separate compensation of 2-wire and 4-wire
measurements in the resistance functions.
Non-volatile input-offset compensation adjustment is available only when the rear panel
calibration keyswitch is in the
ENABLE position and the CAL legend is not shown on the
main display.
Adjustment is performed by initiating an input zero operation with the 8508A in this
condition, using the INPUT menu as described in Chapter 3 or using the IEEE 488 input
zeroing commands described in Chapter 4. Apply a high-integrity low-thermal emf 4-
wire short to the input terminals for this operation. Following adjustment for a particular
combination of function, range, and input a compensation is stored for the corresponding
non-volatile input zero, and the Zero legend is shown on the main display. The Zero
legend may be removed from the display without affecting the stored non-volatile
compensation by using one of the following operations:
1. Power the instrument down.
2. Press the
CLEAR key and make any of the selections from the CLEAR menu.
3. Entering
CAL mode.
Routine Adjustment
The 8508A is a Digital Reference Multimeter offering state-of-the-art performance. This
procedure is intended as a guide for qualified metrology personnel who have access to a
standards laboratory with equipment available to support an instrument of this level of
accuracy. It reflects the adjustment process used by Fluke to perform 8508A adjustment
implemented in an automated system, but as a manual procedure for users to follow. The
procedure is based on the following assumptions:
1. Users are familiar with relevant best measurement practice.
2. Users will take precautions to avoid introducing errors from sources such as thermal
emfs, leakages, electromagnetic interference, etc.
3. Users will make adequate allowance for equipment stabilization and measurement
settling times.
This routine adjustment procedure describes the adjustment points and sequence of
operations required to adjust the 8508A and assumes calibration standards of adequate
traceable uncertainty are available – in this case a Fluke 5720A calibrator and 5725A
amplifier used with an 8508A-7000 Calibration Kit. The procedure assumes the user is
able to adjust and characterize the calibration standards, without describing the process
required to do so.
Characterization of the 5720A/5725A combination allows the 8508A to be adjusted with
uncertainties lower than otherwise available from that equipment. The characterization
process determines the 5720A/5725A errors from nominal at the values required for
8508A adjustment, and may be performed using Fluke’s recommended verification
procedures appearing in the 5700A/5720A Service Manual as a guide. If a characterized
5720A/5725A combination is available where the error from nominal at the various
points required is known, those errors may be taken into account during 8508A
6-9
To Next Page
Loading...
