Manual - 8500A Series Peak Power Meter - Giga-tronics

Theory of Operation
written into the U10 DAC will force the voltage at the thermistor bridge to the desired level to produce
the required power level from the oscillator.
U18A is the buffer for the incoming +10V reference voltage. Q10 and Q11 are controlled by the B6
connection of U9 to provide a signal which can supply current to turn on a relay external to the PPM for
special applications.
A3 Test Points
The test points in Table 4-2 can be checked for the correct signals on the A3 GPIB/Cal Control board:
Table 4-2. A3 Test Points
Test Point
TP1
TP2
TP3
TP4
TP5
TP6
TP7
TP8
TP9
+5 V
5 V Common
-15 V
15 V Common
Description
Output of the control amplifier for the Calibrator control. Its
voltage (ranging from a few hundred mV to 10 V) will be related
to the power required by the Calibrator.
+15 V
Measure from TP7 to TP3 to give an indication of the current
through the oscillator. Will be between 1 and 30 mA.
+10 V
Output of the thermistor bridge. Typically will have a voltage of
about 7 V under ambient conditions.
Manual No. 20790, Rev C, November 1998 4-7
Superceded by Revision D, March 2009