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<12. Troubleshooting>
12-3
IM 11M12A01-02E 16th Edition : Mar. 19, 2020-00
If Alarm 10 is generated simultaneously, a failure in the cold junction system on the detector
terminal block is suspected. In this case, follow the procedure according to troubleshooting for
Alarm 10 in 12.2.2.5.
If Alarm 11 is generated simultaneously, a failure in the thermocouple system located in the
detector heater is suspected. In this case, follow the procedure according to troubleshooting for
Alarm 11 in 12.2.2.6.
If this failure occurs immediately after the power is supplied, the polarity at thermocouple input
connection (TC+, TC-) on the converter may be reversed. Check the connection from the
detector.
Causes considered for cases where Error2 occurs independently are shown below.
(1) Faulty heater in the detector (heater wire breakage)
(2) Faulty thermocouple in the detector
(3) Faulty cold junction sensor located at the detector terminal block.
(4) Failure in electrical circuits inside the converter
(5) Heater temperature control overcurrent limiting triggered.
(6) TC+ ,TC- thermocouple terminals wired to detector with reverse (wrong) polarity.
Overcurrent protection is triggered if there are problems in the heater wiring. When the protective
circuit is triggered, the internal fuse blows and the heater is disconnected, resulting in Error 2
(temperature failure).
<Locating cause of failure, and countermeasures>
(1) Turn off power to the converter.
(2) Remove the cable from terminals 7 and 8 of the detector and measure the resistance value
between these terminals. The heater unit is normal if the resistance is lower than about
90 Ω. If the resistance value is higher, failure of the heater unit is suspected. In this case,
replace the heater unit (refer to Section 11.1.3, Replacement of the Heater Unit). In addition,
check that the wiring resistance between the converter and detector is 10 Ω or less.
(3) Ensure that TC+ terminal (terminal 3 in detector) is connected to converter TC+ terminal,
and TC- terminal (terminal 4) is connected to converter TC- terminal.
(4) Remove the wiring from terminals 3 and 4 of the detector and measure the resistance
value between these terminals. The thermocouple is considered normal if the resistance
value is 5 Ω or less. If the value is higher than 5 Ω, it may indicate that the thermocouple
wire has broken or is about to break. In this case, replace the heater unit (refer to Section
11.1.3, Replacement of the Heater Unit). Also, check that the wiring resistance between the
converter and detector is 10 Ω or less.
(5) Even if items (2) to (4) are normal, the heater overcurrent protection fuse may have blown.
Check for wiring problems such as the following:
(a) Heater terminals shorted.
(b) Heater terminal(s) shorted to ground.
(c) Heater terminals shorted to power supply.
If the internal fuse blows, this cannot be replaced by the user. Contact your Yokogawa service
representative.
NOTE
Measure the thermocouple resistance value after the temperature difference between the
detector tip and the ambient atmosphere has decreased to 50°C or less. If the thermocouple
voltage is large, accurate measurement cannot be achieved.