Technical data

Calibration Procedures 3
34980A Service Guide 53
DMM Test Considerations
Errors may be induced by ac signals present on the input leads during a
self- test. Long test leads can also act as an antenna causing pick- up of ac
signals.
For optimum performance, all procedures should comply with the
following recommendations:
• Assure that the calibration ambient temperature is stable and 
between 18 °C and 28 °C. Ideally the calibration should be 
performed at 23 °C ±1 °C.
• Assure ambient relative humidity is less than 80%.
• Allow a 1.5- hour warm- up period with a copper short connecting pins
3, 4, 8, and 9 of the ABus connector. Connector pinout is shown in the
figure on page 52.
• Use shielded twisted pair PTFE insulated cables to reduce settling and
noise errors. Keep the input cables as short as possible.
• Connect the input cable shield to the source LO output. Except where
noted in the procedures, connect the calibrator LO source to earth
ground.
• Either remove all modules from the mainframe, or reset the modules to
ensure no module is connected to the backplane ABus.
Because the instrument is capable of making highly accurate
measurements, you must take special care to ensure that the calibration
standards and test procedures used do not introduce additional errors.
Ideally, the standards used to verify and adjust the instrument should be
an order of magnitude more accurate than each instrument range full
scale error specification.
For the dc voltage, dc current, and resistance gain verification
measurements, you should take care to ensure the calibrator’s “0” output
is correct. If necessary, the measurements can be referenced to the
calibrator’s “0” output using Mx + B scaling (see Chapter 2 in the 34980A
User's Guide). You will need to set the offset for each range of the
measuring function being verified.