New digital sensor with square wave output

Diesel Progress North American Edition, March, 2007

Inprox Sensors has developed a square wave output digital sensor technology platform targeted toward the gas and diesel engine markets. The inGen Linear Direct system uses a suite of harsh-duty, noncontact, frequency-based digital sensors that run on an integrated circuit capable of interfacing directly with a microprocessor without the need for internal or external signal conditioning.

The sensor system is used to measure changes in pressure, temperature, linear position, angle and vibration, and works by using frequency of oscillation. This provides an output in the form of a square wave, which is then read through a pulse train by a digital microprocessor. Multiple outputs, such as position and temperature, can also be read by the inGen sensor using the same signal. Because the sensor uses a time-based technology, it does not rely on amplitude or signal shape, which translates into less interference to impact the signal quality.

"Our natural square wave output coupled with this kind of performance/ cost dynamic is really interesting to our customers," said Derek Weber, Inprox vice president, sales North America. "With today's microprocessors' ability to measure thousands of Hz, the resolution is an order of magnitude better than existing technology. The key is the way in which the inGen signal is generated in the first place--a sensor without the need for any signal conditioning."

Inprox developed the inGen sensor to replace less responsive analog technology. "Standard analog methodology requires A/D (analog-to-digital) signal conversion," said Weber. "If the underlying signal is unstable and prone to error, then the pulse train will only multiply and compound these errors and inaccuracies.

"Analog sensing can be like trying to see through a dirty window when your fundamental bit information is inaccurate. Direct to digital outputs create a reliable pulse train where compound error terms that are the cause of most inaccurate and unstable sensor signals are no longer an issue."

All major component costs such as the signal conditioning circuits and analog-to-digital converters have also been removed from the design of the inGen sensor, which Inprox said makes it a more cost-effective product. Inprox initially targeted the sensor toward the aerospace and automotive industries but to date, it has been used in an array of gas and diesel engine applications including camshaft speed-position sensing; fuel injector rack, throttle and injector positioning; turbocharger boost pressure and oil level sensing.

The sensor is also designed for commercial and military use, and with its -166[degrees] to 842[degrees]F temperature range and 1202[degrees]F survivability rating, can be used in extreme temperature applications. "The most impressive attribute isn't just the ability to operate or service in these temperatures," Weber said, "but the strain of cycling through temperatures actually strengthens the sensor itself. At the end of the life of certain systems, this sensor might actually be the component in the best shape."

Inprox Sensors is headquartered in Boston, Mass., with locations in Eastern and Western Canada, India, China and Japan. The company's portfolio features measurement systems, embedded sensing products and a full range of inductive proximity, photoelectric, ultrasonic, laser, capacitive, ultraviolet, magnetic, safety and fork sensors.