Appliance Design - February 2008 - (Page 30) CONTROLS & SENSORS positioning over open-loop control (sensing motor drive parameters only), but typically has been a costly and complicated addition to the system assembly. ITC technology offers a cost-effective solution by removing the complexity on both the sensor-integration side and on the motor-control system side. For speed-control applications where speed is directly proportional to the supply voltage (as with a DC motor), or for applications where speed is related to the switching frequency (as with an AC induction motor or 3-phase induction motors), the ITC sensor platform offers a high-resolution, fast-dynamic-response, highaccuracy approach over the range from zero to full speed. While there are many non-contact optical and magnetic encoder systems available, many designers of motor-control systems have found the ITC technology to be an attractive option. For example, ITC has worked with DC motor manufacturers on control applications that involve rotary actuator position measurement using inGen Direct technology. In one particular design, the change in the integral of dielectric in the field created by the sensor transducer changes reactance in the transducer and thus the frequency. In this case, a one-lobe cam was used for a target with a pair of sensors in order to produce a quadrature output. The target is fixed to the rotating shaft. The system gives absolute zero speed/ position measurement, as well as direction of rotation and rotary speed. The same signal-processing methodology is used as in the previous temperature example above. Alternately, a single sensor can be used with a multi-toothed wheel to give an incremental indication of speed and position. Benefits of using this approach include: 1. Low measurement hysteresis. 2. True zero speed output with one sensor. 3. Not effected by dust, oil, moisture, etc. 4. Lightweight targets can be used. (Aluminum, metal-coated plastic, etc.). 5. Minimal effect from motor EMI. 6. Fast dynamic response. Signal refresh to 500 kHz or more. 7. Longer MTBF from fewer components. 8. Digital output. 9. Low power consumption. 10. High resolution. 11. Real time self-diagnostics. Continuous sensor output can be monitored for fault conditions/ pre-warning. Oven sensor array provides rack detection during self-clean cycle. and data transmission. Motor speed control Another potential application for inGen Direct sensors is in the realm of motor speed control. The obvious purpose of a closed-loop (feedback-based) motor speed controller is to receive a signal representing the actual speed, compare that to the demanded speed, and then adjust to drive the motor at the demanded speed. With a number of variables affecting motor speed (load, friction, temperature, etc.), sensing motion plays an integral part to the motor control system. Feedback-based speed control offers better motor control and Innovate Turn to Invensys Controls for innovative engineering solutions. Flexible options Reduced development time Faster market penetration We understand your challenges and we have what you need – like our Invensys Range Controls. LCD touch screen. Our extensive product and system integration offerings can pack the WOW into your residential and commercial range applications. Contact us today at 630.260.3052 or innovate@invensyscontrols.com. Innovate with the appliance controls leader. Invensys® and InnovatIT™ are trademarks of Invensys plc., its subsidiaries and/or affiliated companies. Innovation you expect For more Information Enter 111 30 applianceDESIGN AD02084Inven.indd 1 Digital sensors improve closed-loop motor speed control. www.applianceDESIGN.com 1/14/08 1:27:44 PM February 2008 http://www.appliancedesign.com
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