Under Pressure: Transducers and Testing

Fri, 06/01/2007 - 7:58am
When Steve Asselin, a project manager and specialist in automated test measurement, came to Heat Transfer Products Inc., his initial assignment was to design a production line for the company's Munchkin water heaters. Heat Transfer Products in East Freetown, MA, manufactures water tanks and water heating appliances. Its Munchkin line consists of ultra high-efficiency stainless steel heaters.

Asselin knew that the most important aspect of designing the new production line would take place during the final stages of assembly: the testing stage during which each boiler would be checked for its ability to perform — literally — under pressure. Asselin contacted Setra Systems in Boxborough, MA, to get the test measurement devices he needed for this essential testing phase. Setra Systems is a manufacturer of electronic instrumentation for measuring pressure, acceleration, and weight.

Setra's Paul Richards recommended the Model 201 pressure transducer, which at that time was a prototype. Asselin set up two testing lines for the Munchkin boilers with the transducer coming into play during the boiler firing rate test, which is when the boiler is tested to make sure it is firing at its designed rate so that it will produce the amount of heat it's rated for. During the test, water from a 2,400-gallon tank is pumped through the boiler. The boiler is then lit. As the boiler heats up, gas flow into the boiler and other parameters are measured to determine the firing rate of the boiler. In order to determine the gas flow rate accurately, the pressure of the gas flowing into the boiler must be known. The Model 201 transducer is used to measure this pressure. The transducer features an Inconel diaphragm and an insulated electrode, which forms a variable capacitor. As the sensor pressure increases or decreases, the capacitance changes. This change in capacitance is detected and converted to a fully conditioned, easy-to-read linear current output signal.

The Model 201 transducer is suitable for this kind of application because of its rugged design, wide operating range (-40°F to +175°F), and high overpressure capability (45 psi). In addition, its all-welded, no o-ring construction makes it leak-free so that it can measure hazardous gasses, and its patented variable capacitance sensor allows it to measure very low differential or gauge pressures.

More information about pressure transducers is available by contacting Setra Systems, Boxborough, MA, at 800-257-3872 or by visiting


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