Pressure Range: An important criterion for accurate water levels

Addressing frequently asked questions about both the pressure range of Diver dataloggers and the pressure range in relation to the Diver “suspension depth” – often referred to as “cable length”.

This article addresses frequently asked questions about both the pressure range of Diver dataloggers and the pressure range in relation to the Diver “suspension depth” – often referred to as “cable length”. In this post we will help you choose the right Diver pressure range to ensure water levels are monitored as accurately as possible.


Let’s clear up some confusion around pressure and suspension depth


In our conversations we hear that it is assumed that a monitoring point with a suspension depth of 100 meters also requires a Diver with a pressure range of 100 meters,  and that it is not always clear that the accuracy of the Diver datalogger decreases with a higher pressure range.

In order for water levels to be monitored as accurately as possible the following chart summarizes the most important information on the pressure range of Diver dataloggers to assist with the selection of the correct Diver pressure range.


Van Essen Instruments offers Diver dataloggers with 4 pressure ranges:

  • Available in 10, 20, 50, and 100 meter water column
  • A Diver pressure sensor with a pressure range of 10 meters will accurately measure a water column of up to 10 meters.
  • Configured with a safety margin of 50% (also referred to as the ‘overload pressure’ in our specifications) ensures the Diver pressure sensor will not malfunction until the water column reaches 15 meters. 


Did You Know?


The pressure range determines the accuracy of the Diver datalogger and consists of a pressure sensor with a ceramic membrane that is deformed under the influence of pressure.

The degree of deformation is an accurate indication of the pressure and a thicker and less flexible membrane can withstand a higher pressure (a larger water column).

However, this thicker membrane is less sensitive to small pressure changes and therefore less accurate. For example, a TD-Diver with a pressure range of 10 meters has a maximum accuracy of ±2.0 cmH2O, while the maximum accuracy of a TD-Diver with a pressure range of 100 meters is ±20.0 cmH2O.

 

It is important to take the Diver pressure range into account when you want to start monitoring groundwater and the first consideration should be to determine the measurement objectives such as – “Is there is only interest in water level measurements, or are water quality parameters like electrical conductivity (EC) and temperature also important?” In the latter case it is recommended to place the Diver in the middle of the monitoring well screen to ensure that the EC and temperature recorded are representative for the water in the surrounding aquifer. If only water levels need to be monitored there is no need to place the Diver in the middle of the screen – just make sure that the Diver is positioned below the lowest possible water level.

The required Diver pressure range can be determined based on the correct suspension depth and the highest possible water level – the maximum expected water level fluctuation.

A greater pressure range is only required in situations where large fluctuations of water levels are present, for example near a groundwater abstraction well.

In summary, when monitoring water levels, a Diver with a pressure range of 10 meters is the best option and this Diver will provide the highest level of accuracy available.


Click here to use our interactive tool that will help you find the correct Diver cable length for your project.