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8.2.4 Additional Troubleshooting
General
Verify that piping of analyzer and flow rates are correct. Verify that wiring of analyzer is correct.
Power Supply Fault
30 V supply — Measure voltage between sensing-unit terminals 14 (hot) and 13 (common.). It should read
30 +2, –6 volts. Actual value depends upon current drawn by heaters.
Temperature Control Inoperative
Heater voltage — Measure voltage between the sensing-unit terminal given below (hot) and terminal 13
(common).
Terminal F. Warmed-up (at 50 °C); 19 ± 3 V. Cold start from (25 °C); 2.5 ± 0.5 V
Terminal J. Warmed-up (at 50 °C); 30 +2, -4 V. Cold start from (25 °C): 28 ± 3 V.
Heater thermistor voltage — Measure voltage between the sensing-unit terminal given below (hot) and
terminal 13 (common).
Terminal G. Warmed-up (at 50 °C): 6.2 ± 0.2 V. Cold start from (25 °C): 6.2 ± 0.2 V.
Terminal H. Warmed-up (at 50 °C): 3.1 ± 0.1 V. Cold start from (25 °C): 1.5 ± 0.5 V.
Zero and Span Check — measure current in Sensing-unit Terminal 12
Zero gas (air) – Sensor output current to be between 250 uA and 450 uA.
Range 1 – Sensor output current to be approximately 1.5 mA at 100 % CO
Range 2 – Sensor output current to be approximately 12 mA at 100 % CO
Range 3 – Sensor output current to be approximately 3 mA at 75 % H
Resistance Check (Sensor Card Disconnected)
R8 = 2078 ohms ± 0.1 %
R10 = 2000 ohms ± 0.1 %
Temperature Control Thermistors
50 °C, 122 °F, R= 3.6 K ohms ± 5 %
25 °C, 77 °F, R = 10 K ohms ± 5 %
Heaters, R = 30 ± 3 ohms (one pair)
Measuring Cell (WR to WB wires)
50 °C, 122 °F, R = 2024 ohms ± 20 %
25 °C, 77 °F, R = 5000 ohms ± 20 %
Reference Cell (WR to WG wires)
50 °C, 122 °F, R = 2024 ohms ± 20 %
25 °C, 77 °F, R = 5000 ohms ± 20%
Measuring and reference cells resistances should be matched to 1 %.
Test for short circuit between leads of each of the above components and case ground.
9/06
7866 Triple Range Digital H
and CO
Analyzer/Indicator - Operation and Maintenance
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Troubleshooting
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Table of Contents
Troubleshooting
