Keysight 8478B, Руководство по эксплуатации и обслуживанию

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Keysight 8478B Thermistor Mount 37
Maintenance
Troubleshooting
Troubleshooting
Exceeding the CW or pulse power limits of the Model 84 78B Thermistor Mount
may result in damage such that the mount will no longer zero on the power
meter.
Before adjusting the mount in any way, make sure that the mount is the cause
of the problem. An open or short indication, using the performance test or the
check in below means that the mount is not repairable by the procedure
outlined in the following paragraphs. However, the mount may be
nonoperative, but still repairable. Test for this by using the thermistor resistive
match test procedure, or by connecting the mount to a power meter and cable
which are known to be good. A faulty cable will not have continuity through the
respective connector pins, or may have poor contact at the mount connector.
Poor contact will show up as intermittence or a great deal of noise (visible on
the power meter) when the cable is gently flexed near the connector end.
To troubleshoot a damaged mount, proceed as follows:
1. Connect mount to Model 432.
2. Set:
3. Rotate COARSE ZERO from one limit to the other.
If meter remains pegged upscale, the thermistor elements have been
damaged. However, it may be possible to re-compensate the thermistors and
return the mount to operation; otherwise they must be replaced. In either case,
the Effective Efficiency and Calibration Factor data on the nameplate are no
longer valid (refer to “Repair and Recalibration” ).
If meter remains pegged downscale, measure resistance between pins 1 and 2,
and pins 3 and 4. The resistance should measure between 1000 and 5000
ohms. An open or shorted reading indicates the need for replacement of the
thermistors.
MOUNT RES: 200 Ω
RANGE: COARSE ZERO
POWER: ON
Under no conditions should the mount be required to carry a current
higher than 14mA.