Agilent Technologies 34970A, Руководство по обслуживанию, Страница: 73 / 273

Test Considerations
To ensure proper instrument operation, verify that you have selected
the correct power line voltage prior to attempting any procedure in
this chapter. See “If the Instrument Does Not Turn On”, on page 42.
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 2-hour warm-up period with a copper short connected and
the multiplexer module installed before verification or adjustment.
The connections are shown in the figure on page 66.
•
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.
Two-wire Ohms measurements are affected by the entire path length,
including the plug-in card trace length and slot trace lengths. On the
34901A, Channel 10 is recommended as the median path length
(on the 34902A, use Channel 8) for 2-wire Ohms verification and
adjustments. Install the input multiplexer in slot 200.
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 page 54 ). You will
need to set the offset for each range of the measuring function being verified.
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Chapter 4 Calibration Procedures
Test Considerations
71