ETS-Lindgren HI-1710A Microwave Oven Survey Meter - Manual (Page 48)

48 Theory of Operation www.ets-lindgren.com
When not in the Peak Hold mode, the bar graph display responds to the filtered
signal as displayed.
The system performs a series of self-tests at startup and each time the probe is
zeroed. The bias voltage is measured to check for defective diodes and for a
proper bias supply, and then the offset voltage of the array is measured. The
offset voltage is the signal at the preamp output with the probe in a zero RF field.
Limits on the offset voltage check for proper probe/preamplifier operation. A zero
chamber option is available to minimize the RF present at the probe head during
zeroing; see Zero Receptacle Option on page 11. A stimulus voltage is applied to
the input of the first operational amplifier stage in the preamp. This signal is used
to test the integrity of the RF signal path. The level of each of the four power
supply outputs is tested on startup. If an error is detected, the parameter screen
will be displayed with the erroneous value flashing. Upon zeroing, the self-test is
repeated until all errors are corrected.