Instruction manual

SM425 INSTRUCTION MANUAL 12.0 TROUBLESHOOTING

If an Error-2 occurs immediately after power is supplied, the polarity of the thermo-couple input

connection (TC+, TC-) in the converter may be reversed. Check detector connections.

Possible causes of an Error-2 condition 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 of the converter electronics

5. Heater temperature control overcurrent limiting triggered.

6. TC+ and 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, an internal fuse blows. The heater is then disconnected, resulting in an Error 2

(temperature failure) condition.

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 will be normal if the resistance is lower than about 90Ω.

If the resistance value is higher, failure of the heater unit is suspected. In this case, replace the

heater unit (refer to Section 1.59.3, “Replacement of the Heater Unit”). In addition, check that the

wiring resistance between the converter and detector is 10Ω 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 between

these terminals. The thermocouple is considered normal if the resistance value is 5Ω or less. If

the value is higher than 5Ω, damaged thermocouple wiring may be the cause. In this case,

replace the heater unit (refer to Section 1.59.3, “Replacement of the Heater Unit”). Also, check

the wiring resistance between the converter and detector is 10Ω 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:

• Heater terminals are shorted together.

• Heater terminal(s) are shorted to ground.

• Heater terminals are shorted to power supply.

Do not attempt to replace an open internal fuse. Contact your Teledyne Monitor Labs service

representative if this occurs.

• Measure the thermocouple resistance after the difference between the detector tip temperature and the

ambient temperature decreases to 50°C or less. Accurate resistance measurements cannot be made at

high temperatures.

190 42500001 REV A