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.