Many of the sensing problems that confront engineers involve measuring position or distance. Contactless sensing techniques provide a preferred method for many measurements, but the technology to provide the desired performance can vary considerably. Depending on the application, Hall Effect, magnetic, ultrasonic, optoelectronic, and laser displacement sensors offer quite different solutions. This section includes sensors designed with each of these approaches as well as an example of a signal conditioner IC for sensing applications and an application-specific temperature sensor.
CONTACTLESS POSITION SENSOR
Melexis' new, patented MLX90316 CMOS Hall sensor detects the absolute angular position of a small magnetic field parallel to the IC's surface. Using two pairs of conventional planar Hall plates for each of the two directions parallel with the IC surface (X and Y), the sensor identifies the position of the magnet above the device. Ferromagnetic structures then amplify the external magnetic field and concentrate it on the Hall plates. The unit performs full 360 degree sensing with a single die SO8 package and provides full redundancy with dual die in a TSSOP16 package. The sensor encodes a mechanical angle into two 90 degree phase-shifted (sine and cosine) signals, which are then amplified, sampled, and converted in the digital domain using a CoRDiC algorithm that performs an iterative rectangular-to-polar transform. The output signal can be either an analog signal, a PWM signal, or a SPI digital signal since the digital value can be converted back into the analog domain. Designed for angle measurements in both industrial and automotive, potential applications include rotary position system, gas / brake pedal, throttle valve, ride height, steering wheel, and joystick motion. For more information on Melexis' MLX90316, go to http://rbi.ims.ca/4416-710.
ENCAPSULATED PROXIMITY SENSOR
Massa's TR-2445/210 ultrasonic air transducer is an encased solid plastic housing that operates in the 210 kHz frequency region. In non-contact echo ranging applications a single transducer transmits a short duration acoustic signal, and then receives the reflected echo. Alternatively, one unit serves as a transmitter and a second unit is a receiver. The peak frequency response is 210 kHz with a bandwidth of -3 dB at 7 kHz and -6 dB at 25 kHz. Transmitting sensitivity is 110 dB (dB re 1µPa/V at 30 cm) with receiving sensitivity of -191 Db (dB re 1V/µPa). Target applications include proximity detection, robotics, level measurement, mechanical positioning roll diameter measurement, thickness control, and more. For more information on Massa Products' Model 18A/40 go tohttp://rbi.ims.ca/4416-709.
CONTACTLESS ABSOLUTE POSITION SENSOR
TT electronics OPTEK Technology has developed an inductive sensor for a wide range of vehicle and automotive applications. The Autopad technology uses a movable disc that interacts with a magnetic field generated on a fixed portion, or pad, by a series of transmit and receive coils to determine absolute position. The disc changes the magnetic filed phase generated by the pad and multiple discs can be used with a single pad to provide automotive engineers 360 angular and linear displacement sensing. The sensor's nonlinearity is less than 1 percent, with 0.1 percent resolution (at 10 bits), and an input/output rate of 1kHz. With an analog (ratiometric), pulse-width modulated (PWM) output, or a specified automotive BUS protocol, potential automotive applications include chassis height sensors, headlamp leveling, ride height and suspension control systems, pedal and steering sensors, and throttle position sensors, among others. For more information on Optek's Autopad inductive sensor technology, go tohttp://rbi.ims.ca/4416-711.
DIFFERENTIAL HALL IC FOR AUTOMOTIVE APPLICATIONS
Infineon's TLE4925(C) differential Hall IC detects the motion and position of ferromagnetic and permanent magnet structures by measuring the differential flux density of the magnetic field. Fast start-up occurs with the second detected edge. The high sensitivity (Bmin less than 1.5 mT), low jitter (typically ±0.11 percent at 10 mT) units take advantage of a dynamic self-calibration principle, use advanced digital signal processing for offset cancellation, and provide a digital output. The sensors have short- circuit, reverse polarity, and over-temperature protection of the output. The module style package has two 4.7 nF capacitors integrated between the leads for enhanced electromagnetic compatibility (EMC). Units require no external components for operation. Target automotive applications for the smart Hall Effect sensor include crankshaft and transmission measurements. For more information on Infineon's TLE4925C differential Hall IC,go tohttp://rbi.ims.ca/4416-712.
HIGH POWER DIGITAL ULTRASONIC SENSORS
Keyence's digital ultrasonic sensors are multi-reflective devices with a maximum detection range of 39.37 inches (FW-H10R). The design incorporates an Active Wave Stabilizer (A.W.S.) algorithm and an external shift function that provides stable detection in severe environments. The response of the FW-410R at 39.37 inches is 1,000 msec and is 150 msec at 5.9 inches. The FW Series sensors can detect glass, metal, liquid levels or other targets that could be difficult to detect with reflective-type photoelectric sensors and measurements are not affected by the target's color, pattern, or luster. For more information on Keyence's digital ultrasonic sensors, go tohttp://rbi.ims.ca/4416-713.
LONG DISTANCE REFLECTIVE SENSOR
Optek Technology has developed a reflective sensor, the OPB720 Series for optoelectronic sensing in commercial plumbing fixtures. The sensor consists of a synchronized infrared LED and photosensor packaged in plastic housing measuring 1.1×0.68×0.33 inch (27.9×17.3×8.4 mm). The unit can detect the absence or presence of objects from 0.04 inch (1 mm) to over 24 inches (610 mm). The proximity sensor has a current of 50 mA dc, with power dissipation of 300 mW. Custom options include cable length, reflective distances, and terminations options. The Series permits plumbing engineers to implement non-contact, automatic faucets, bathroom fixtures, and soap dispensers with preset factory sensing distances at lower costs than traditional proximity sensors. Other potential applications include moving sidewalks, escalators, and product dispensing systems. For more information on Optek OPB720 Series, go to http://rbi.ims.ca/4416-714.
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