Operation; Biasing Thermistors; Maximum Input; Average Power - Keysight 478A Operating And Service Manual

Thermistor mount

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Operation

CAUTION

may destroy the match between thermistors and increase susceptibility to drift.

Before connecting the model 487A to the 431 or 432 power meters, set the

CAUTION

MOUNT RES switch to 200 W position. CONNECTING A 200 W MOUNT TO A

POWER METER SET FOR A 100 W MOUNT CAN RESULT IN THERMISTOR

DAMAGE.

The model 478A/431 and 478A/432 combinations respond to the average RF

power applied. The maximum signal applied to the thermistor mount should not

exceed the limitations for

– pulse energy

– peak pulse power

Excessive input can permanently damage the model 478A by altering the match

between RF and compensation thermistors (resulting in excessive drift or zero

shift) or cause error in indicated power.

Average Power

The 478A/431 and 478A/432 combinations can measure average power up to 10

mW. To measure power in excess of 10 mW, insert a calibrated directional coupler

such as one of the Keysight Technologies model 770 series or 790 series between

the mount and the source. UNDER NO CIRCUMSTANCES APPLY MORE THAN 30

mW AVERAGE POWER TO THE MOUNT.

echanical Shock: Do not drop or subject to severe mechanical shock. Shock

Keysight 478A Operating and Service Manual

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