Troubleshooting RDE300 series RTD temperature sensors

Occasionally the Pt100 or Pt1000 RTD temperature sensor on an RDE300 series unit may read incorrectly.

When temperature is out of range or cannot be read correctly, the RDE300 unit will not be able to calculate irradiance or soiling ratio, since temperature is an input to the calculations. 

For example, RDE300 Series Engineering Client Software may display NaN for both PV temperature and Irradiance, as shown below:

In addition, the Event Log in RDE300 Series Engineering Client Software may display an error as shown below:

You may check the function of the RTD using the following steps, which may only be performed by qualified personnel:

1. Disconnect power to the RDE300.
2. Open the RDE300 enclosure. WARNING: Even though power is disconnected, hazardous voltages may be present. These instructions should only be performed by trained and qualified personnel.
3. Locate the RTD#1 and RTD#2 inputs as shown below, indicated by red arrows.
4. Take a photograph of the connector to record the wire colors.
5. Disconnect the connector of the RTD channel to be inspected.
6. Disconnect the RTD wires from the connector.
7. Use a digital multimeter to measure the resistance between each pair of wires.  At least one pair will read resistance of near 100 ohm (Pt100) or 1000 ohm (Pt1000), with exact value depending on the current temperature. Other pairs (corresponding to sense wires) will read a low resistance likely <10 ohms, depending on RTD cable length.
8. Record the resistance readings along with their corresponding wire color pairs. 
9. Rewire the connector (using the photo acquired previously).
10. Reinstall the connector.
11. Close the enclosure securely.
12. Reconnect power to the RDE300

Send your resistance readings to Atonometrics for confirmation of findings.

If the RTD resistance values are incorrect, the RTD or associated sensor, such as PV1 reference cell, may need replacement.

If the RTD resistance values are correct, but your RDE300 series unit still does not read temperature correctly, there could be a software configuration problem or a PCB malfunction.

Atonometrics will advise how to proceed.