Teledyne GFC-7000E - Trace CO2 Analyzer - Manual (Page 215)

Model GFC7000E Instruction Manual TROUBLESHOOTING & REPAIR PROCEDURES
04584 Rev A1 204
• Measure the voltage across TP3 and TP1. With proper flow (800 sccm at the sample inlet)
this should be approximately 4.5V (this voltage will vary with altitude). With flow stopped
(sample inlet blocked) the voltage should be approximately 1V. If the voltage is incorrect,
the flow sensor is bad, the board is bad or there is a leak upstream of the sensor.
11.4.7. Motherboard
11.4.7.1. A/D Functions
The simplest method to check the operation of the A-to-D converter on the motherboard is to use
the Signal I/O function under the DIAG Menu to check the two A/D reference Voltages and input
signals that can be easily measured with a voltmeter.
1. Use the Signal I/O function (see Section 11.1.3 and Appendix A) to view the value of
REF_4096_MV and REF_GND. If both are within 3 mV of nominal (4096 and 0), and are
stable, ±0.5 mV then the basic A/D is functioning properly. If not then the Motherboard is
Bad
2. Choose a parameter in the Signal I/O function such as SAMPLE_PRESSURE,
SAMPLE_FLOW, CO
2
_MEASURE or CO
2
_REFERENCE. Compare these Voltages at their
origin (see Interconnect drawing 04215 and Interconnect list 04216) with the voltage
displayed through the Signal I/O function. If the wiring is intact but there is a large difference
between the measured and displayed voltage (±10 mV) then the Motherboard is bad.
11.4.7.2. Analog Outputs: Voltage
To verify that the analog outputs are working properly, connect a voltmeter to the output in
question and perform an analog output step test as described in Section 6.9.3.
For each of the steps, taking into account any offset that may have been programmed into
channel (see Section 6.9.4), the output should be within 1% of the nominal value listed in the
table below except for the 0% step, which should be within 2 to 3 mV. If one or more of the steps
fails to be within this range then it is likely that there has been a failure of the either or both of
the DACs and their associated circuitry on the Motherboard.
Table 11-10: Analog Output Test Function - Nominal Values Voltage Outputs
FULL SCALE OUTPUT VOLTAGE
100MV 1V 5V 10V
STEP % NOMINAL OUTPUT VOLTAGE
1 0 0 0 0 0
2 20 20 mV 0.2 1 2
3 40 40 mV 0.4 2 4
4 60 60 mV 0.6 3 6
5 80 80 mV 0.8 4 8
6 100 100 mV 1.0 5 10
11.4.7.3. Analog Outputs: Current Loop
To verify that the analog outputs with the optional current mode output are working properly,
connect a 250 ohm resistor across the outputs and use a voltmeter to measure the output as