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Adjustable speed drive system for centrifugal fan

  • US 4,158,527 A
  • Filed: 10/22/1976
  • Issued: 06/19/1979
  • Est. Priority Date: 08/26/1976
  • Status: Expired due to Term
First Claim
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1. A method of controlling operation of a centrifugal fan comprising:

  • (a) providing a centrifugal fan with a means whereby upset conditions in a system receiving air from said fan can be monitored and correction action initiated,(b) providing an artificial pressure limitcurve above the operation curve representing the expected spectrum of normal fan operation,(c) monitoring the operation of the centrifugal fan by measuring its actual output pressure at the then existing flow rate and generating a first signal, determining the existing flow rate and the desired pressure for the fan at the existing flow rate, generating a second signal representing said desired pressure,(d) comparing said first and second signals,(e) generating a third signal when as a result of said comparison the actual fan pressure signal exceeds the desired pressure signal at the then existing flow rate by a predetermined amount and is at least equal to a point on said limit curve.

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