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Motor On/Off Sensing Device by Monitoring the RF Conducted Noise

IP.com Disclosure Number: IPCOM000043882D
Original Publication Date: 1984-Oct-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Pennell, GF: AUTHOR [+4]

Abstract

The operation of an electrical motor generates radio frequency (RF) noise which is both radiated and conducted. An air flow sensing system for determining the on/off condition of blowers, fans and other motor driven devices is achieved by detecting this conducted RF noise produced by the motor as it operates, and not just as power is applied. The pick-up device 11 (Fig. 1) is, in effect, a transformer having a single-turn primary, formed by the motor lead through the toroid. The secondary 12 is thirty turns of #30 insulated wire, which goes to the detector logic 13. Pick-up device 11 can be located anywhere along the power feed 14 to the motor 15 on the load side of the filter 16, if one is used. The detector logic 13 (Fig. 2) shows that the secondary 12 of the pick-up device 11 is connected to the input of amplifier 17.

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Motor On/Off Sensing Device by Monitoring the RF Conducted Noise

The operation of an electrical motor generates radio frequency (RF) noise which is both radiated and conducted. An air flow sensing system for determining the on/off condition of blowers, fans and other motor driven devices is achieved by detecting this conducted RF noise produced by the motor as it operates, and not just as power is applied. The pick-up device 11 (Fig. 1) is, in effect, a transformer having a single-turn primary, formed by the motor lead through the toroid. The secondary 12 is thirty turns of #30 insulated wire, which goes to the detector logic
13. Pick-up device 11 can be located anywhere along the power feed 14 to the motor 15 on the load side of the filter 16, if one is used. The detector logic 13 (Fig. 2) shows that the secondary 12 of the pick-up device 11 is connected to the input of amplifier 17. The selective gain of amplifier 17 is determined by capacitor 18, inductor 19 and resistor 20 providing amplification at the frequency where it is required and limiting the gain at other frequencies, i.e., 60 Hz. The output of amplifier 17 is used to charge capacitor 21 whose voltage is then compared, by amplifier 22, to a voltage level established by resistor 23 and resistor 24. When the charge voltage on capacitor 21 exceeds the voltage at the junction of resistor 23 and resistor 24, the output of amplifier 22 decreases to logic '0', indicating the motor is operating. This approac...