Measuring Water Tank Contents Using Computerised Calibration

Under the name of Castello, Keller AG has introduced a flexible, modular system for the accurate indication of the content of a liquid in a tank.

Castello offers a user-friendly way to represent the pressure measurement at the bottom of a tank as the quantity of remaining liquid. At the push of a button, the microprocessor performs the calculations using the information of the tank shape and dimensions and displays the remaining tank content quantity on the clearly legible 5-digit LED display in the desired unit (litres, gallons etc.).

Easy to use software to configure Castello is free of charge. It contains the most current tank shapes yet, at the same time, other tank shapes can be easily integrated at the factory. Exclusive use of absolute pressure sensors in the Castello system eliminates the use of capillary vented cables with all the problems associated with a gauge pressure measurement.

The Castello enclosure integrates an air pressure sensor, ranged between 0,8 bar and 1,3 bar absolute. The sensors to measure the hydrostatic pressure at the bottom of the tank are calibrated from 0,8 to 1,8 bar abs for tanks up to 5m in height, and 0,8 to 2,3 bar abs for tanks up to 10m in height. The pressure difference, calculated by the μP, is the relative hydrostatic pressure.

The overall accuracy of the system of 2 mbar is achieved using a computerised calibration and compensation procedure for the pres¬sure sensors. The coefficients for this calculation are stored in EEPROMs in the sensors. These are retrieved by the microprocessor at each measurement and employed within the equations to calculate the pressure values. The Castello enclosure and hydrostatic sensor can be interchanged at will.

The power supply to the system is provided by a 9 V compound battery and is sufficient for at least 6000 measurements with a five second display duration. Another feature is that the Castello is IP65 waterproof.

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