Yokogawa Integral Oxygen Analyzer ZR202 - Manual (Page 170)

IM 11M12A01-05E 12-7
12. Troubleshooting
12.2.2.5 Alarm 10: Cold Junction Temperature Alarm
The equipment incorporates a temperature sensor. An alarm is issued when the sensor
temperature exceeds 858 C. If internal temperature of this equipment exceeds 858 C, the
electronics may fail.
<Locating cause of failure, and countermeasures>
This equipment can be used at ambient temperatures up to 558 C. If the ambient tempera-
tures may exceed the limits, take appropriate measures — such as applying heat insulat-
ing material to the furnace walls, and adding a sun shield to keep out direct sunlight.
If this alarm occurs even when the ambient temperature is under 558 C, the electronics
may be defective. Contact your local Yokogawa service or sales representative.
12.2.2.6 Alarm 11: Thermocouple Voltage Alarm
This alarm is generated when the emf (voltage) of thermocouple falls below -5 mV
(about -1708 C) or exceeds 42.1 mV (about 10208 C).
(1) A failure of the thermocouple at the detector occurred.
(2) A failure of the electrical circuits occurred.
<Search for cause of failure and taking measure>
(1) Turn off the power to the analyzer.
(2) Remove the probe from the analyzer. Also remove all the connectors between the
converter and probe. Measure the resistance of the heater wire (yellow wire) from the
probe as indicated in Figure 12.5. The heater unit is normal if the resistance is lower
than about 90V. If the resistance is higher than that value, the heater unit may be
defective. In this case, replace the heater unit (refer to Section 11.1.3, “Replacement
of the Heater Unit”).
F12.2E.EPS
Multimeter
(V)
Heater wire
Figure 12.5
(3) Next, check the resistance of the thermocouple from the probe. Use a multimeter to
measure the thermocouple resistance between terminal 3 (red cable connected) and
terminal 4 (white cable connected) as indicated in Figure 12.6.
The thermocouple is normal if the resistance is 5V or less. If the value is higher than
5V, the thermocouple wire may be broken or about to break. In this case, replace the
heater unit (refer to Section 11.1.3, “Replacement of the Heater Unit”).
CAUTION
• Measure the thermocouple resistance value after the difference between the probe tip
temperature and the ambient temperature decreases to 508C or less. If the thermo-
couple voltage is large, accurate measurement cannot be achieved.