There are several things that you should check if your sensor is showing erratic readings:
Ensure that your sensor is running the latest version firmware. Contact us to make sure that you have the latest version relevant to your sensor. You will need to quote your unit serial number when getting in touch.
Ensure that the heater set point is set to 30°C or higher.
Ensure that some sort of data averaging has been applied, either within the sensor (using the sensor’s internal filtering) or in the computer/data logger.
Check your cables are properly connected and ensure shielding is terminated at both ends of the cable. Refer to the Installation Section of your User Manual for further advice.