Customised differential pressure module
By B Vetterli, Keller
Published in the October 2014 issue of Electricity+Control (pages 42 – 44)
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A spraying system that allows precise metering of lubricants was required for sheet metal working. This application was the starting point for Bürkert to develop a series of liquid flow controllers, and it served as the pilot project. The sensor and control technology, the actuator and the customary electrical process interfaces had to be accommodated in one compact device that was to be designed for trouble-free continuous operation, as is usually the case in process measurement technology.
Flow rate measurement using differential pressure
The process environment called for a fairly robust design and high operating reliability, therefore it was decided to measure the flow volume on the basis of the pressure drop in the measuring medium as it passes through a metering orifice with a defined diameter. Moreover, two individual pressure sensors were to be deployed for this purpose. In fact, the company had introduced a differential pressure transmitter that could deliver the key features required in this instance especially in terms of overload capability.
In conventional differential pressure transmitters, both sides of a measuring diaphragm are exposed to the measuring medium; ie one ‘high’ and the other ‘low’ pressure input. With typical differential measuring ranges of 500 mbar and common mode pressures of up to 10 bar, a momentary interruption of either the high or low pressure could result in a 20-fold overload on the diaphragm. Such an overload can only be absorbed with complex (and therefore expensive) adaptations to the structural design, without which the transmitter would inevitably be destroyed. Bürkert’s fluid control systems specialists wanted to exclude risks of this sort, so they were very interested in the differential pressure measurement module.
- A differential pressure measuring module, developed in response to a client’s request, is integrated into a production flow controller.
- Optimised solutions come from close collaboration between a component producer and a device manufacturer.
- The module has been deployed in numerous applications.