There are only three possible failure modes for an IRt/c sensor. If an IRt/c sensor is installed and does not function as expected, the failure may be due to something other than the sensor. It is recommended that the sensor is checked out for response after installation to ensure that it is connected to the readout instrument properly. This can be done simply by placing a hand or a heat source in front of the sensor after it is installed and making sure the reading changes (this is still valid even if the temperature is well below the calibration point). If the sensor gives a reading very different from the expected reading:
Troubleshooting Steps
- Check initial calibration. If the controller has been changed, or the offset adjusted after the sensor has been installed, the temperature reading may be very different from the actual temperature.
- Check the sensor lens. If dirt has accumulated on the lens over time, then the reading may be lower than expected. Clean the lens using a Q-tip and alcohol. The lens needs to be treated gently, it can be easily scratched.
- Check sensor impedance. If the sensor reading does not change even thought the target temperature is changing, the sensor may be burnt out. Check the impedance of the sensor; if the impedance is >15kohm, then the sensor is probably burnt out. If the impedance is <100ohm, then there is a short in the thermocouple wire and the temperature being measured is at the short.
- Check for hermetic seal compromise. If the temperature suddenly reads about half of what it should, then the hermetic seal may be compromised and the Xenon gas may have escaped.
Diagram Description
The diagram illustrates an Exergen IRt/c sensor connected via a cable to a readout instrument. The readout instrument appears to be a panel-mounted device with multiple indicator lights or controls. The cable connects to the sensor, which has a cylindrical body and a lens at the front. Several close-up views are provided: one showing the electrical connection within the sensor head, another detailing the lens and its mounting, and a third illustrating the sensor tip and its field of view. These details help in understanding the physical construction and potential points of failure or inspection.
Troubleshooting Table
| Symptom | Action | Result |
|---|---|---|
| 1) Sensor reads high | Check initial calibration | Adjust zero offset of readout to bring reading back to normal. |
| 2) Sensor reads low | Clean lens of sensor | If sensor does not correct, check points 3 and 4 below. |
| 3) Sensor reading does not change | Check impedance of sensor | If sensor reads open, replace. If sensor has impedance of a few 10W, then there is a short in the t/c wire. |
| 4) Sensor reading suddenly drops by about half | Check through points 1 to 3 above | If still reads low, replace sensor. |
Additional Information
For more information regarding the calibration testing of IRt/c sensors, see Tech Note #74. For process control applications, the system can be programmed to check the sensor circuit every time it is powered up, see Tech Note #39. If a PLC is used for process control, a sensor short will have the same effect as a “Heater Burn Out Protection” feature.
Contact Information
Exergen Corporation office:
USA
400 Pleasant Street
Watertown, MA 02472
Tel: +1 617 923 9900 press 4 for industrial
Fax: +1 617 923 9911
Exergen Industrial International/OEM Sales office:
Clever IR
The Netherlands
Pastoor Clercxstraat 26
5465 RH Veghel
Tel: +31 (0)413 376 599
Email: industrial@exergen.com
Website: www.exergen.com
