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Induced draft fan control for use with gas furnaces

  • US 5,720,231 A
  • Filed: 11/16/1995
  • Issued: 02/24/1998
  • Est. Priority Date: 06/09/1995
  • Status: Expired due to Fees
First Claim
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1. A method for monitoring operating conditions of an induced draft fan electric motor of a gas furnace system having a microprocessor to control the speed of the electric motor to ensure that adequate back pressure and flow rate for safe and efficient furnace operation exist including the steps oftaking an electric motor and fan to be used in the system and operating the motor over a selected range of back pressure from a back pressure value when the motor is unloaded to a maximum back pressure based on the design of the furnace system,taking a plurality of readings of first and second parameters proportional to speed and torque of the electric motor as first and second variables over the selected range to generate a curve of the first variable vs the second variable and storing the variables in a memory location of the microprocessor,selecting a minimum and maximum value of acceptable back pressures,on a continuing basis, during normal operations of the induced draft fan electric motor when used in the system, taking readings of actual operating values of the first and second variable,comparing the actual operating variables with the stored variables proportional to motor speed and torque at the maximum and minimum values of acceptable back pressures;

  • andif the actual operating variables are above the maximum point on the curve or below the minimum point on the curve, deenergizing the system.

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