A gem of a device for water tasks

Dec 29, 2011 | Flow & Level

Advances in pressure transducer technology, combined with the affordability of such devices, make them an obvious choice for use in water processing. Mike Powers, product marketing director for Gems Sensors and Controls, explains the technology used in these transducers and shows how they can enhance system performance

With dependability such an important issue in the processing of clean and waste water, the use of pressure transducers can provide a way of maintaining and protecting both systems and product quality. These devices can withstand aggressive process conditions, extremes of temperature, mechanical shock and vibration while delivering precise control. For example, within a system that is handling abrasive slurries, a constant measurement of pump discharge pressure via transducers will reveal whether a system is coping with a blockage. If so, the transducer can trigger appropriate action that can prevent the pump from generating high pressure in excess of the operating limits of the piping system.

Converting pressure into signals

A pressure transducer converts pressure, typically that of fluid or gas, into electrical output signals. Inside a pressure transducer is a strain gauge sensor, mounted on the back of a stainless steel diaphragm, the face of which is in direct contact with the pressure media. Displacement of the diaphragm thus causes the strain gauge to flex, either in compression or under tension, with the electrical output being directly proportional to the pressure or vacuum applied. Output from the sensor is connected to onboard electronics, with the entire unit being contained within a stainless steel housing.

Strain gauge sensors, which contain this pressure sensitive diaphragm, can be manufactured using the sputtered thin film process. The application of the sputtered thin film layer during the manufacture of pressure transducers results in a sensitive, robust sensor that is suitable for direct contact with almost all liquids, oils and gases.

Compact, accurate devices

Chemical vapour deposition (CVD) technology is another method of manufacture, producing compact, accurate devices. CVD sensors can be mass produced at low cost, since they are produced on wafers in large batches.

Advances in electronics technology have also made a strong and positive impact on the efficacy of pressure transducers. The integral electronic signal conditioning that has been supplied with these devices over recent years often incorporates advanced ASIC (application specific integrated circuits) technology. This allows the performance and functionality of each transducer to be tuned to meet the specific requirements of each customer. As with CVD, the benefits of ASIC technology have included reductions in manufacturing costs and, consequently, unit costs for the end user.

Gems Sensors and Controls manufactures a range of submersible pressure transducers using CVD, including the 2600 Series. These devices can be used in clean water applications and offer stability and accuracy in a variety of enclosure options rated at IP65 and above. For contact with grey and black water, the 5000 Series has an open face construction that allows the transducer to deliver accurate results in presence of viscous liquids and solids without clogging.

Affordability

With such components now being available at affordable prices, pressure transducers are now incorporated in a a variety of water and wastewater treatment facilities. During tests these devices have measured a response of 1ms or less to changes in pressure, accuracy with almost zero drift over time and an operating life in excess of 100 million cycles. These levels of performance and reliability have been welcomed by the water and wastewater processing sector, not only because accuracy is vital to plant safety but also because it is imperative to minimise the potential for maintenance and component replacement where equipment is difficult to access.

Pressure transducers offer robust performance even amid the harsh or corrosive media elements found in applications such as desalination plants or sewage sludge processing, while the resistance of these devices to constant vibration enables them to be used in proximity to pumps, useful for water processing applications.