Output Goes Negative - Teledyne 3020M Operating Instructions Manual

5 Maintenance
Note that preamp test does not tell anything about sensor condition. If
preamp is ok but instrument is not performing then sensor, sensor power
supply, and sensor interconnection cable are suspects.
5.6

Output Goes Negative

If during operation of the instrument, gas pressure exceeds 20 psig, the
output of the sensor may reverse polarity, readings on the display may go
negative. If this happens:
Turn power off by unplugging the instrument.
Turn gas pressure to less than 20 psig.
Turn power on again.
Return instrument to analyze mode.
5-4
Analog
0 OK
1 DAC A (0–1 V Concentration)
2 DAC B (0–1 V Range ID)
3 Both Failed
Preamp
0 OK
1 Zero too high
2 Amplifier output doesn't match test input
3 Both Failed
Teledyne Analytical Instruments
Model 3020M