
Chapter Five: Maintenance
Fault Isolation
33
PRESSURE IN
+15 Volts
SGND
10K + 5%
5.1K + 5%
Figure 5: Inserting Two Resistors to Replace the Pressure Sensor Signal
This will produce an input voltage of +9.6 to +10.3 Volts. To produce a zero input, simply short
out the 10K
Ω
resistor. Set the front panel engineering units switch to the “mmHg” position. Use
an external meter to measure the output voltage for this channel (not the “DC OUTPUT”).
Reference the meter to SGND on the input connector. The output voltage should track the input
voltage developed by the above network to within ±0.2 Volts. If not then the problem lies in the
channel amplifier and zero circuit. Refer to the circuits involving U1, U2 and U3 in order to
troubleshoot to the appropriate component. If the voltage does track but the front panel DVM does
not agree, the problem is with either the engineering units resistive divider (R43-R54), relay K1
(PDR-C-2C only), the front panel READ or engineering units switch, or buffer U8. Note that the
DVM is 1.9999 Volts full scale and will read out
1
/
10
of the incoming signal voltage when set to the
“mmHg” position (ignoring decimal point).
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