Datalogger Recording Unstable Readings

1. Introduction

Dataloggers can be affected by changing conditions on site or a specific event on site. This can lead to them giving variable and unstable readings. The following tests will help to identify the root of the problem.

2. Fault Finding Tests

Testing of sensors in question. Determining whether the sensors are functioning correctly should be the first step, as this can immediately rule out the datalogger as the cause. If a manual readout is available disconnect the sensor(s) from the datalogger, take a few readings and compare with the previous datalogger reading. For In-Place-Inclinometers (IPIs) a multi-meter can be used to measure the output mV reading from the instruments by powering the sensor with a 12V supply. With vibrating wire transducers it is possible to test whether there has been a failure in the transducer or in the cables with specific tests that can be found in the back of the piezometer manuals.

Testing of cables. This can involve a visual check to make sure there are no loose connections where they are wired in to the datalogger as well as checking the cables themselves to ensure there are no cuts or nicks that could indicate a cable break.

Swapping of sensor locations. If it appears that only one or two of the sensors on the datalogger are faulty we would suggest swapping their positions with other sensors that are still giving stable readings to see if there is any change in their output readings. 

Swapping of components. This would only be possible if you have multiples of components or spare components such as multiplexers or AVW200s. If you do, it is possible to swap out the potentially faulty components with other components to further narrow the possible causes of the unstable readings.