Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 255)

Troubleshooting & Repair Model 9110TH NOx Analyzer
Teledyne Analytical Instruments 235
7.5.10. MOTHERBOARD
7.5.10.1. A/D functions
A basic check of the analog to digital (A/D) converter operation on the motherboard is
to use the Signal I/O function under the DIAG menu. Check the following two A/D
reference voltages and input signals that can be easily measured with a voltmeter.
 Using the Signal I/O function (Section 4.13.2 Appendix D), view the value
of REF_4096_MV and REF_GND. If both are within 3 mV of their
nominal values (4096 and 0) and are stable to within ±0.5 mV, the basic
A/D converter is functioning properly. If these values fluctuate largely or
are off by more than 3 mV, one or more of the analog circuits may be
overloaded or the motherboard may be faulty.
 Choose one parameter in the Signal I/O function such as
SAMPLE_PRESSURE (see previous section on how to measure it).
Compare its actual voltage with the voltage displayed through the SIGNAL
I/O function. If the wiring is intact but there is a difference of more than
±10 mV between the measured and displayed voltage, the motherboard may
be faulty.
7.5.10.2. Analog Output Voltages
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 4.13.3.
For each of the steps, taking into account any offset that may have been programmed
into the channel (Section 4.13.5.4), the output should be within 1% of the nominal value
listed in the table below except for the 0% step, which should be within 2-3 mV. If one
or more of the steps is outside of this range, a failure of one or both D/A converters and
their associated circuitry on the motherboard is likely.
Table 7-9: Analog Output Test Function - Nominal Values
FULL SCALE OUTPUT VOLTAGE
100mV 1V 5V 10V
STEP % NOMINAL OUTPUT VOLTAGE
1 0 0 mV 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