Digital sensors: Sensor technology provides digital output

-- Control Engineering, 1/25/2007

Inprox Sensors has been developing a technology they call 'linear direct sensor platforms' for use in aerospace-industry speed and linear position measurement. The company has been working actively and quietly for the last 2 years with some of the largest automotive, aerospace and appliance makers in the world to adapt the technology to their critical applications

They've applied the technology specifically to advanced linear variable differential transformer (LVDT) replacements, and as speed-measurement devices for high temperature runout and material deformation sensing. The devices Inprox has developed so far provide micron resolution precision distance measurement with both ferrous and non-ferrous targets coupled with error-free data communications.

They have also applied the technology in the automotive market for advanced steering, various position and brake-wear sensors, and in the appliance markets for low cost, high volume applications among laundry and cooking manufacturers.

What makes this sensor technology unique is an innovative integrated circuit to interface between the sensor itself and the measurement system front end, and the design of a tuned oscillator for encoding the analog signal in digital form. The digital sensor technology puts out a square wave that can interface directly with microprocessors without the need for analog-to-digital conversion, signal conditioning. The microprocessor reads this output as a pulse train.

The technology's advantages include adaptability to digital control equipment; and improvements in system reliability, as well as reduced sensitivity to electrical noise, temperature drift and common-mode variations on the ground bus. In addition, the technology offers higher precision sensing resolution, better dynamic response; greater linearity, durability, longer mean time before failure, lower hysterisis, higher stability, lower costs, more immunity to interference, an easier process of transmission and extended capabilities for multiplexed signals. The ability to operate in high temperature environments (-110 to 450 C, and up to 650 C for the linear position sensors) is an added benefit.

The technology has only begun to reach its full potential. 'We would not be surprised if in 5 years customers were adopting digital frequency of oscillation output sensors in preference to analog devices,' said a company's salesperson. 'As understanding of the technology's great benefits reach a market break point, [we expect to see] a spill over effect. The momentum of large users in automotive, aerospace and industrial markets will drive smaller OEM's end-users towards this technology.'

—C.G. Masi, Senior Editor