Technical performance of selected pressure transducers used for groundwater monitoring under laboratory and field conditions

Over recent years the British Geological Survey (BGS) has been involved with research on shallow groundwater systems using a limited range of pressure transducers to monitor groundwater level and temperature. However, there have been concerns regarding their accuracy, precision, electronic drift and temperature compensation, which have limited data interpretation in some cases. This study aimed to evaluate technically the existing range of pressure transducers held by the BGS Groundwater Science Programme against a range of alternative commercially available transducers, sourced from previously unused manufacturers/suppliers. Laboratory testing included accuracy, precision and temperature compensation assessments. Field testing involved deploying all instruments in an on-site borehole for 99 days. Sensor readings were compared against frequent dip measurements to assess instrument field accuracy and potential drift. Laboratory accuracy tests indicated the majority of sensors performed within the product specification. The most accurate units were considered to be Transducers B, C, G and O which recorded all water level changes to within the experimental error. Precision was generally under ± 1.5 mm, with the exception of Transducers I to M and Transducers G and O which ranged between ± 3.6 and 74.2 mm. Temperature compensation was regarded as a concern on Transducer G, I, J, K and N. Field accuracy was generally to within around ± 10 mm, with the exception of the higher range models. Some sensors also clearly demonstrated decreasing accuracy over time, i.e. drift. This appeared to be of linear or curved forms in some transducers, although was not clearly identifiable in many others. The most accurate sensors, and inherently those with the least drift, were absolute Transducer H and vented Transducer F.