|
The simplest way to troubleshoot an RTD is to use an ohmmeter. Since the RTD must have some amount of original resistance at room temperature, one should be able to disconnect and isolate its leads so its resistance may be measured. If the RTD is platinum, the amount of resistance should be approximately 110 Ω. The next step would be to heat the RTD and see if the resistance increases. Even though one may not know the actual temperature, this field test will indicate if the RTD can change resistance as its temperature changes. Remember, the resistance change may only be a few ohms. If the resistance does not change or if the resistance is infinity ∞, the RTD should be replaced. The most common problem with RTDs is that the wire that is used for the sensor will break and cause an open circuit. If the original resistance reading of the RTD is infinity ∞, it indicates the RTD is open and it must be replaced. It's also possible for the RTD to become shorted, which would cause the resistance reading to be near zero and it would not change as the temperature changes. After one has determined that the RTD is operational, its circuit may need to be calibrated. A calibration tester is available that is basically a precision Wheatstone bridge, which allows one to measure the amount of resistance the RTD provides for each temperature throughout its range. One must also be able to accurately control the temperature for each reading if the calibration is to be successful. |
|
|
Using the RTD as a Motor-Starting Switch | |
|