Pressure Sensors / Detectors / Transducers
SETRA's Inductive Sensing Transducer is High Pressure Answer for Test Stand Manufacturer
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Whitney Systems of Chelmsford, MA builds a wide range of customized machinery designed to enhance productivity and product quality. The company designs and manufactures everything from machines for custom automation to O-ring insertion machines to test stands such as electrical testers, flow rate testers, endurance testers and leak testers. Unfortunately, after creating one such test stand, a ball valve leak tester for their customer, Metso Automation, Whitney learned that it was relying on a far from sufficient test measurement device.
Whitney had built a machine that tested Metso's different ball valves for pressure decay. Metso makes cast iron, steel and brass ball valves which are used in a range of applications, including plumbing, air, water and HVAC applications. Metso's X-Series metal and soft seated ball valves are a key element in the most demanding, high-cycling applications. They feature an innovative shaft/ball connection which works to assure tight shut-off, even with the lowest pressure differentials.
Whitney's ball valve leak tester is designed to provide comprehensive leak testing for the X-Series and other Metso ball valves. The machine is designed to test for pressure decay in four locations: at the stem of the ball valve handle, on either side of the ball, as well as through the ball itself. The operator puts the ball valve into a "nest" in the machine, and hits the start button which initiates the formation of a pressure seal around the ball. An electric actuator is used to send signals which cause the ball valve to open and close. Finally, a number of pressure transducers on each machine are used to pinpoint and measure pressure drops.
A transducer fails the test.
Unbeknownst to Whitney, when initially creating this ball valve leak tester for Metso, they had incorporated a faulty transducer. The company that manufactured this transducer had changed its ratings, and not notified Whitney of the change. So while the machine was testing for ball valve leaks, the transducer actually ruptured - it literally couldn't handle the pressure, with the machine requiring testing at 150 psi. To make matters worse, Whitney sent the transducer back for repairs and, shortly after its return, the component ruptured again.
According to Whitney Systems president, Mark Whitney, locating the exact cause of the problem wasn't as easy as it should have been. He said, "When the old transducer broke, it took four to six weeks to figure out that our supplier had changed the rating on us."
Clearly Whitney needed to upgrade to a new transducer, but finding one that could meet they requirement of this ball valve tester wasn't easy. The transducer would have to be able to measure both very low pressure differential changes as well as high line pressures.
Meeting the highest pressure demands
"We looked at a couple of transducers that could meet some of our needs, but they couldn't satisfy the 150 psi requirement," Whitney said. "When we spoke with Setra, we realized that they not only had a transducer that was rated to handle our high pressure needs, but they had it available, off the shelf, without requiring any customization. Within a very short period of days, we were back up and running with Setra's Model 235 pressure transducer in place."
Setra Systems Inc.'s Model 235 differential pressure transducer is actually designed for high line pressures up to 2500 psig. Used also in municipal gas distribution, oilfield gas recovery, coal mine ventilation and electricity generating plants, this versatile pressure transducer was exactly what Whitney needed.
According to Setra sales manager, Paul Richards, "The Model 235 is unique in its ability to accurately measure from the highest and to the lowest line pressure changes. The Model 235 virtually eliminates the need to balance the high and low pressure at installation to minimize line pressure error on a differential measurement. Users can expect a miinimal low line pressure effect of <0.1% FS change per 100 psig line pressure change."
Said Whitney, "The Model 235's utmost accuracy allows us to ensure that the ball valves fall within Metso's acceptable leak rate of 45 cc per minute. Setra's patented technology was a great fit for both our application and our budget."
A unique inductive technological advance.
The Model 235's excellent performance, typical to more expensive differential pressure transducers, is achieved through Setra's unique inductive sensing technology. Unlike capacitive transducers, the Model 235 contains no liquid filled diaphragm and is not media-sensitive. This eliminates the possibility of batch contamination and thermal transient errors, as the only wetted parts exposed to media are stainless steel, alumina ceramic and glass. The transducer does not, in fact, measure fluid - it measures changes in a magnetic field.
The Model 235 is accurate to +/- 0.18% of full-scale output, with a total error band of +/- 0.5% full scale over the compensated temperature range of -20° to +160° F on 5 psid through 500 in. W.C. pressure ranges. There is virtually no shift in output at warm-up, and a typical update rate of 25ms makes thus unit ideally suited for pressure applications that require a stable, fast response - applications like Whitney's ball valve leak tester.
"Since we started using the Setra 235, we haven't had any problems," Whitney concluded. "The transducers have proven both accurate and durable. In fact, we just recently bought our fourth transducer for the Metso test stands."
With high line pressure transducers in place, the people at Whitney Systems are actually feeling quite a bit of pressure relief. And their customers, like Metso can rest easier knowing that their ball valves are production-ready, having already passed the most stringent of pressurized performance tests.
CONTACT:Charlene Cloney
Gray & Rice Public Relations
617-367-0100 ext. 107
cdcloney@gr2000.com
