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Fan-Failure Detector Circuit

IP.com Disclosure Number: IPCOM000047713D
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Boerstler, DW: AUTHOR

Abstract

In this fan-failure detector circuit, a light-emitting diode illuminates a spot in the path of a fan blade and a light-detecting diode detects light reflected from a reflective spot on one blade. As the blade rotates, the light-detecting diode produces a sequence of up-level pulses that are spaced apart by the period of fan rotation. A single-shot circuit is connected to be set by the pulse from the light-detecting diode. The period of the single-shot is just longer than the normal period of rotation of the fan, and while the fan runs at its normal speed the single-shot remains reset. If the fan speed fails, the single-shot completes its timing sequence and produces an up logic level at its output.

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Fan-Failure Detector Circuit

In this fan-failure detector circuit, a light-emitting diode illuminates a spot in the path of a fan blade and a light-detecting diode detects light reflected from a reflective spot on one blade. As the blade rotates, the light-detecting diode produces a sequence of up-level pulses that are spaced apart by the period of fan rotation. A single-shot circuit is connected to be set by the pulse from the light-detecting diode. The period of the single-shot is just longer than the normal period of rotation of the fan, and while the fan runs at its normal speed the single- shot remains reset. If the fan speed fails, the single-shot completes its timing sequence and produces an up logic level at its output. The circuit includes a timer that starts when the fan is turned on and runs long enough for the fan to come up to its operating speed. The output of this timer is dot ANDed with the output of the single-shot to hold the output at a down level during this normal period of slow fan speed. Circuits for several fans can be connected in a chain to produce an output at the last circuit if any fan fails. The output of each circuit is supplied to the next circuit through an inverter so that an up level at the inverter output signifies a normal speed for the fan of the preceding circuit. The inverter output signal is dot ANDed with the fan detector signal at the input of the single- shot. Thus, the light detector pulses are inhibited from setting t...