Differences between thermocouple and glass fiber temperature measurements

In order to compare thermocouples and fiber-optic sensors, our experts attached the various sensors to the motor supply wire on an imc demo test stand and then produced a visualization of the measurement.

In the test setup, the sensors were mounted near the motor on a screw terminal on the supply wire. The phase voltage is measured at this clamping point by means of a sense cable, which is protected against contact by a transparent shrink sleeve. In our test we fixed the thermocouple to the shrink tubing from the outside with cable ties. The glass fiber was inserted into the shrink tubing and placed directly at the contact point.

The diagram shows the following measurement data:

  • Temperature via thermocouple (blue)
  • Temperature via glass fiber (red)
  • RPM (orange)
  • Phase current of the motor (green)

The curve shows that a strong deviation can be detected between the temperature measurements. The signal coming from the thermocouple (blue) shows a sinusoidal disturbance which correlates with the phase current of the motor and depends on its frequency.
The following characteristic curve shows that a temperature error of ± 15°C was measured here. Temperature measurement via glass fiber, on the other hand, shows an interference-free measurement signal.
Our whitepaper lists further advantages of fiber-optic measurement technology.

Attachment of thermocouple and fiber-optic sensor to the motor supply wire
Temperature development of the sensors
Report with characteristic curves of the motor
Report with characteristic curves for voltage, rpm, speed and torque