Buttressed-diaphragm sensor monitors pressure extremes

Parsippany, NJ--The customer's need was simple: a lightweight, low-cost indicator to signal when hydraulic-line pressure fell below 15 psi. Simple, except that the indicator had to withstand exposure to 2,000-psi static pressures and operate repeatably between -100F and 400F. Calls to the rest of the industry had produced only laughter, the customer said.

Charles Liucci of Artisan Electronics Corp., had the answer in a week, and the company delivered the product within six. His DiaLast(TM) indicator uses the force of fluid pressure over a diaphragm to tip the balance of forces between a set of magnets and an opposing set of springs.

Above a given pressure, the sum of the fluid force and the magnets' attractive force compresses the springs, and the unit's indicator button can be manually reset. When the pressure falls below a level determined by the spring and magnet combination, the springs drive the magnets apart, and the button pops up.

Liucci says that the most important element in the design is the membrane diaphragm buttressed by the lower magnet carrier. "It fits like a glove over the carrier's semi-spherical surface, so it can withstand tremendous pressure even though it's thin," he explains. The diaphragm's contour permits the 0.13-inch excursions between actuation and rest necessary to overcome the coercive force of the magnets.

The diaphragm had to be thin because of the sensor's wide temperature range. Although a thick diaphragm might withstand the pressure without support, it would stiffen at low temperatures, throw off the unit's calibration, and increase hysteresis and deadband.

Arriving at the proper balance of nonlinear magnetic forces, linear spring forces, and pressure-diaphragm force might seem like more than a week's design work. Liucci says that the proper way to approach the problem is through computer modeling and optimization, but time constraints would not allow for that. Instead, he called on more than fifty years of experience "playing" with magnets to arrive at a workable design empirically within a week.

Other Applications
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  • Process controls

  • Fluid
    power

"The design has a wide setpoint span with exceptional repeatability," explains Dan Booton, director of sales and marketing at Artisan. "It fit within the specified size and weight constraints and replaced a very expensive transducer, making the customer's design viable."

Dialast's success led to a number of subsequent variations including electronically switched versions for remote pressure sensing and temperature/viscosity-compensating models. With an auxiliary pressure port available in the magnet side of the diaphragm chamber, the indicator can read absolute or differential pressures.

Additional details...Contact Dan Booton, Artisan Electronics Corp., 5 Eastmans Rd., Parsippany, NJ 07054, (201) 887-7100.

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