Pressure Sensors Get Smarter

February 12, 2007
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New sealed pressure sensors that shield against most electromagnetic interference (EMI) and provide more reliable readings may help improve HVAC system efficiency, service, and maintenance. According to Sensata Technologies, the new 2CH pressure sensor allows the use of pressure sensors in HVAC applications previously considered too electrically dense for traditional pressure sensors to operate efficiently in.

Higher system efficiency and improved reliability are the goals for both HVACR manufacturers and end users.

“Reduced warranty events and improved service are the goals this product addresses for system manufacturers,” said Chris Mello, an engineering manager for Sensata Technologies.

“Increased EMI in commercial spaces came with the introduction of inverter-driven compressor systems, from fan controls to the compressors themselves.”

The trend toward increased use of electronic controls was introduced to the North American market through some overseas manufacturers. “It has been requested more and more often by other OEMs,” said Mello.

OVERCOMING LIMITATIONS

In the past, the use of electronic pressure sensors in commercial HVACR systems had been restricted due to the high levels of electrical noise these systems generate. The new product from Sensata is case-isolated, providing a barrier against EMI and enabling HVACR system designers and contractors to integrate reliable and accurate pressure sensors into their systems.

The degree of EMI interference depends on where the unit is located as well as how much EMI the system itself generates, said Mello. The 2CH unit is designed specifically for installation within the a/c unit. This sensor offers resistance from EMI that travels directly to and within the unit. “Our hexport is threaded onto metal fittings like refrigeration lines,” Mello explained. “An electrical charge can build up. It’s attached to our case, but our electronics are isolated from it.”

The 2CH also addresses customers’ needs to maximize system efficiency, said Mello. More-efficient systems tend to use more electronic components. “The more electronics, the more EMI there is,” Nate Strong, field sales engineer for Sensata Technologies, said. “We’re driven by our customer base to respond to their needs and system designs.”

The 2CH pressure sensor features EMI protection of 100 V/m and a dielectric terminal-to-case strength of 1.8 kV. With pressure ranges from 100 to 750 psi and a burst pressure rating of up to four times the operating pressure, the device can be used in “electrically challenging” environments such as inverter pumps and advanced HVACR systems.

“The sensor can be used across a wide range of refrigerants and temperatures,” stated John Forsyth, HVAC marketing manager for Sensata. “System designers can now benefit from an electrically stable, hermetic sensor designed specifically for use in HVACR applications.”

MONITORING, FEEDBACK

The pressure sensor also can be tied into a feedback loop to keep track of system operation, said Mello. “This is real-time monitoring feedback,” offering information on high- and low-pressure conditions, superheat, subcooling, refrigerant charge indication, and direct fan control for variable-speed systems. “With a [pressure] switch, it will turn it on or off,” he said. “The pressure sensor will monitor the system parameters in real time and allow the operation of these systems to be optimized.

“Accuracy from the pressure sensor is key to maintaining system efficiency,” Mello continued. “If the technician assumes they are at a certain pressure but the reading is off, it could affect system efficiency or even damage components.

“Applications for sensors in commercial spaces could be smaller split systems,” he continued. In North America sensors are mainly used in rooftop units and larger chiller systems. “We’ve also applied them to commercial refrigeration and transport refrigeration,” Mello stated.

The sensor provides its pressure feedback in terms of voltage output. This voltage output is fed into system control electronics. Its usefulness to service and maintenance staff depends on where the sensor is applied. “The HVAC maintenance person may not be able to see what the actual charge level is without an efficient, real-time pressure measurement,” said Mello.

MARKET OPPORTUNITIES

Across the board “all large OEMs we are engaged with” are interested in pressure sensors. “We are hearing interest from major OEMs around the globe,” Mello said. “There are potential residential applications as the cost of some of our products continues to be driven down. We’re now in a position to offer some of the benefits of using pressure sensors to the residential air conditioning market.”

In both residential and commercial applications, “We are trying to stay one step ahead of industry trends and new technology adoption rates, coupled with the expected lower cost of components,” Mello said. “Customers are driving us to come up with solutions at a new cost point. On the residential side, they need something with real-time pressure output and low component cost.

“In the residential market, the primary driver will be accuracy of charge,” Mello said. “Overcharging or undercharging both can lead to potential stresses on the system, which can lead to system failure.”

As OEMs continue to be pushed beyond 13 SEER efficiency, “there could be a potential higher rate of adoption in terms of technology,” Mello said, “for charge monitoring and the measurement of subcooling and superheat.” Technicians will be able to look at charge pressure in real time. Computations could be made in an OEM’s control board. “The ‘smarts’ on the electronic board already lend themselves to this type of application,” Mello said.

“The technology is here,” Mello concluded. “At this point it’s more overcoming the hurdle of the cost point. If you apply a pressure sensor on a system, you can reduce warranty claims. That’s the Holy Grail of applications.”

Sensata Technologies, formerly the Sensors & Controls business of Texas Instruments, is headquartered in Attleboro, Mass. For more information, visit www.sensata.com.

Publication date: 01/29/2007

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