Task

A chemical is to be added on a controlled basis to water flowing in an open trench. The metered addition is to be set proportional to the quantity of water flowing through.

Solution

The non-contact ultrasonic level sensor measures the filling height of the trench as a measure of the flow velocity or the flow rate of the water. A surge pipe eliminates the influence of wave movements on the measured filling level. Metered addition of the chemical is controlled by a pneumatically operated diaphragm control valve, whose aperture can be varied by means of a TopControl positioner. The positioner or control valve is activated via the standard signal output of the level sensor.

The function enabling free presetting of a characteristic integrated in the positioner allows the rangeability of the control valve and, thus, the flow rate of the chemical to be matched to the measured filling level or the water flow rate in the trench.