HP 432A, Manual

Page: 22 / 78

Model 432A Section III
Operating Information
3 − 5
1. POWER. Instrument power ON/OFF switch;
connects either ac line voltage or internal
battery (Option 01 only) to internal voltage
regulator circuits. When ac power is on, optional
battery charging circuit operates.
2. COURSE ZERO. Meter zero adjustment; set the
RANGE selector to COURSE ZERO, turn OFF
the RF power, and adjust to zero the meter.
3. RANGE. Power measurement range selector;
selects ranges from 0.01 to 10 milliwatts (-20 to
+10 dBm). COURSE ZERO setting is used to
zero meter with no power applied to thermistor
mount.
4. FINE ZERO. Electronic zero that balances the
compensation bridge with zero RF input. To
zero meter during operation, close the switch
momentarily. Be sure that RF power is not
applied to the thermistor mount when the FINE
ZERO switch is depressed.
5. Meter. Indicates power input to thermistor
mount in milliwatts and dBm. To use the dBm
scale, note the value in dBM of the range in use,
and subtract from it the reading on the meter
dBm scale.
6. Mechanical Meter Zero. Sets meter suspension
so that meter indicates zero. To adjust the zero:
a. Turn POWER switch off.
b. Turn the adjustment screw clockwise until
the indicator falls below zero and comes
back up to zero again.
c. Turn the adjustment very slightly counter-
clockwise to free up the mechanism from
the adjusting peg.
7. CALIBRATION FACTOR. Amplifier gain
compensation selector. Set to correspond to the
calibration factor printed on the thermistor
mount body. See paragraph 3 − 23 for more
information.
8. MOUNT RESISTANCE. Selects resistance
equal to that of mount in use to balance bridges.
Table 1 − 2 lists Hewlett-Packard thermistor
mounts and resistances. Set with meter power
OFF, when mount is initially connected to the
meter.
9. Thermistor Mount Cable Connector. Input
connector for 5-1/2 foot cable that connects to
the 478A, 8478B, or 486A Thermistor Mounts.
Figure 3 − 2. Front Panel Controls, Connectors and Indicators (Sheet 2 of 2)
NOTE: The photograph opposite is for
illustration purposes only.