Teledyne GFC 7001E User Manual download pdf (Page 294)

Troubleshooting & Repair Model GFC7001E Carbon Dioxide Analyzer

Teledyne Analytical Instruments 294

13.5.7. MOTHERBOARD

13.5.7.1. 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.

3. Use the Signal I/O function (see Section 13.1.3 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.

4. Choose a parameter in the Signal I/O function such as SAMPLE_PRESSURE, SAMPLE_FLOW,

CO_MEASURE or CO_REFERENCE.

 Compare these voltages at their origin (see interconnect drawing, P/N 04215 and interconnect list,

P/N 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.

13.5.7.2. Test Channel / Analog Outputs Voltage

The ANALOG OUTPUT submenu, located under the SETUP  MORE  DIAG menu is used to verify that the

GFC 7001E/EM Analyzer’s analog outputs are working properly. The test generates a signal on functioning

outputs simultaneously as shown in the following table.

Table 13-10: Analog Output Test Function - Nominal Values Voltage Outputs

FULL SCALE OUTPUT OF VOLTAGE RANGE

(see Section 7.4.2)

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

For each of the steps the output should be within 1% of the nominal value listed in the table below except for the

0% step, which should be within 0mV ±2 mV. Make sure you take into account any offset that may have been

programmed into channel (see Section 7.4.5).

If one or more of the steps fails to be within these ranges, it is likely that there has been a failure of either or both

of the DACs and their associated circuitry on the motherboard. To perform the test connect a voltmeter to the

output in question and perform an analog output step test as follows:

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Teledyne GFC 7001E User Manual Page 294