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Process transmitters designed for flexibility

Supplier: WIKA Australia By: Bernd Reichert, Head of Process Transmitters, Wika, Klingenberg, Germany
21 April, 2015

Plant operators desire measuring components that are versatile and can be used economically. Wika developed a generation of universal process transmitters for pressure measurement that is tailored for this profile of requirements.

In addition to its primary task, the model UPT-2x can determine, for example, both the level and the volume of tank contents.

Generally speaking, a process transmitter is used for measuring a pressure in pipes and ducts through which liquids or gases are flowing. However, using the hydrostatic pressure in vessels also opens up the possibility of another application, identifying the level by using the 'liquid column' as a reading of the height.

The only requirement for this: The substance being measured and, with this, its density must be known.

The default setting of the UPT is based on the density of 1 kg/dm³, being the density value for water. Any difference in the medium (for example, mineral oil with a density of 0.8 kg/dm³) can easily be implemented in the instrument via the display menu or through its communication software. The height reading is then displayed either in metres, centimetres, millimetres, feet or inches.

To then determine the volume, the only missing data is the maximum filling height of the container. This dimension is input via the measuring instrument‘s display, and thus it displays the volume. Furthermore, with the UPT, vessels with a custom shape can also be included. The transmitter features a HARTv.7 interface for an easy connection of the system.

Via this communication channel, the instrument software can also transmit ‚holding points‘. These are value pairs of height in percent and volume in percent, which the operator has determined through calculation or through a test filling of the tank. The UPT handles 30 such value pairs, through which the form of the tank can be sufficiently described.

This method also works for tank shapes that are, for ex- ample, composed of different bodies. The following figure illustrates the system (for the sake of simplicity given by the example of a horizontal cylindrical tank): When one generates the volume from the fill level, one gets an S-curve.

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