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Circuit for Monitoring Parallel DC Blower Motor Operation

IP.com Disclosure Number: IPCOM000060379D
Original Publication Date: 1986-Mar-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 3 page(s) / 49K

Publishing Venue

IBM

Related People

DeSilva, DK: AUTHOR

Abstract

This article describes a circuit arrangement by which two blower motors can be monitored for proper shaft rotation. A hall effect device built into each motor issues pulses proportional to shaft revolutions. These pulses are integrated to yield a voltage inversely related to shaft speed. A low voltage means the motor shaft is turning adequately. Conversely, a high voltage signals an error. The addition of a logical OR gate to the circuit allows multiple blowers to be monitored simultaneously. The circuit arrangement disclosed herein offers high sensitivity and reliability for monitoring blower motor performance (rpm) when one or more DC blower motors are installed in a housing.

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Circuit for Monitoring Parallel DC Blower Motor Operation

This article describes a circuit arrangement by which two blower motors can be monitored for proper shaft rotation. A hall effect device built into each motor issues pulses proportional to shaft revolutions. These pulses are integrated to yield a voltage inversely related to shaft speed. A low voltage means the motor shaft is turning adequately. Conversely, a high voltage signals an error. The addition of a logical OR gate to the circuit allows multiple blowers to be monitored simultaneously. The circuit arrangement disclosed herein offers high sensitivity and reliability for monitoring blower motor performance (rpm) when one or more DC blower motors are installed in a housing. This is accomplished by connecting the output of the hall effect diodes of each motor to an RC network to control the periodically discharged capacitor in such RC network. If the capacitor voltage exceeds a given threshold level, an output signal is produced to provide an indication that the rpm of one or all of motors has slowed or has stopped completely. Referring to the drawings, Fig. 1 shows the circuit with two blower motor inputs and Fig. 2 shows the various waveforms appearing at different points in the circuit. The monitor circuit for blower motor #1 is the upper branch which includes a transistor 20, an RC circuit formed by resistor 21 and a capacitor 22, a diode 23, transistors 24 and 25, an optional singleshot 26 and a lamp driver circuit 27 which drives indicator 28. Lamp 28 is lit when the rpm of blower #1 has slowed to a predetermined level. This option can be used in applications where microprocessor alarm circuits are not available. The monitor circuit for blower motor #2 is the lower branch which includes a transistor 30, an RC circuit formed by the resistor 31 and capacitor 32, a diode 33, transistors 24 and 25, and the optional single-shot circuit described above. Lamp 28 will also light when the rpm of blower #2 has slowed to a predetermined level. In actual operation, both branches are periodically pulsed by square-wave pulses from the blower motors. These pulses (waveform A) periodically turn on the transistors 20 and 30, to periodically discharge the RC network capacitors 22 and 32. Considering the upper branch, normal operation, the capacitor 22 is discharged by the blower #1 pulse 50 (waveform...