Sensors keep watch over liquid assets

Two products from Gems Sensors are aimed specifically at the problems of obtaining accurate and reliable data from groundwater resources, which are usually in remote locations.

London and the South of England are facing severe water shortages this summer following one of the driest winters on record.

The Environment Agency has reported that the Southern area has received only 75% of normal rainfall, with London being particularly hard hit with only 49%.

Both London Water and Southern Water have warned of impending hosepipe bans, and Sutton and East Surrey Water have acted to impose a sprinkler ban from late April.

The southern region relies on groundwater for almost 70% of its supplies, and levels are being closely monitored by the Environment Agency.

In these circumstances, accurate measurement of groundwater levels is of paramount importance.

Two products from Gems Sensors are aimed specifically at the problems of obtaining accurate and reliable data from groundwater resources, which are usually in remote locations.

Both units are designed to be immersed in the resource being monitored, measuring level based on the pressure of the water above the unit.

Combination of the depth at which the unit is placed and the water pressure provides a very accurate measure of the water level, and the units are triple sealed in slim 20mm diameter 316 stainless steel bodies, which provides maximum usability and minimum maintenance in groundwater applications.

They present significant benefits over previous measuring devices such as mercury manometers, which also represent a health hazard, and shaft encoders which have a high installation cost.

The specific gravity of water changes with temperature, so the units include temperature sensors and an onboard microprocessor which automatically compensates for temperature fluctuations, providing extremely accurate readings: 0.1% total error band over -5 to +45C.

The remote nature of most applications means that battery powered data loggers using SDI-12 protocols are commonly used to collect data from up to eight sensors.

The Gems Series 9500 incorporates the latest microprocessor based digital compensation techniques combined with an ultrastable media-isolated sensor to provide not only high accuracy but also low current draw to maximise battery life.

This makes it the ideal choice for level measurement where SDI-12 loggers are being used.

Gems DCL 9300 digitally compensated level transmitter has been designed to provide the user with the easiest possible installation combined with high accuracy.

The unit can be provided factory set to a specified range, after which no further calibration is required.

The unit just needs to be placed at the required depth and true level can be measured immediately, showing an immediate cost saving on installation and set up.

Both units feature an adjustable range option where the application demands.

Customers can set the range very easily via a user interface module and PC compatible software.

This is the simplest ranging method of any device in the market: ranging of 10:1 of nominal range is achievable.

Onboard calibration data allow the unit to be maintained or reranged without removal from the installation, which reduces down-time and eliminates calibration via a dead weight tester, which is normally a time consuming and costly procedure.

It is estimated that using the Gems units, with their simple installation and calibration and low maintenance, could save around Eur 1500 per site in commissioning costs while delivering the same performance as previous systems using shaft encoders.

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