Noise filtering utilizing running average

• US 5,764,542 A
• Filed: 01/11/1996
• Issued: 06/09/1998
• Est. Priority Date: 01/11/1996
• Status: Expired due to Fees

• Current Assignee: Ranco Incorporated of Delaware (Schneider Electric SE)
• Original Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Inventors: Vitkus, Kimble A., Gaudette, Marvin F.
• Primary Examiner(s): Trammell, James P.
• Assistant Examiner(s): PEESO, THOMAS R
• Application Number:
  US08/584,902
• Time in Patent Office: 880 Days
• Field of Search: 364/557, 364/571.01, 364/574, 364/575, 34/318, 34/445, 34/321, 34/524, 236/91 F, 237/2 R, 374/101, 374/103, 374/116, 374/185, 395/200.32
• US Class Current: 702/179
• CPC Class Codes: G01K 7/21 for modifying the output characteristic, e.g. linearising

Abstract

A system and method for reducing the amount of electrical noise in a signal produced by a temperature sensor for an appliance which utilizes a running average calculation to provide a more accurate sensor reading in an inexpensive and efficient manner. Consecutive readings obtained by the sensor are digitized and stored in a circular buffer. A running average of the readings stored in the buffer is made upon each new reading and the concurrent erasure of the oldest reading.

Claims

1. In an appliance having a sensing element electrically coupled to a microprocessor by a transmission line wherein said sensing element produces a series of values each indicative of a sensor measurement, said values being transmitted over said transmission line as a time varying electrical signal, a method for producing an output value averaged to reduce the effects of electrical noise, said method comprising the steps of:

(a) providing a running average circular buffer including a fixed number of memory storage locations, said buffer including a pointer for indicating a memory location into which a sensor measurement indicative value is to be stored, said buffer being electrically coupled to said transmission line;

(b) receiving a signal indicative of said sensor measurement indicative value;

(c) storing said received value in said buffer at said memory location wherein said memory location had previously stored an oldest sensor measurement indicative value, said oldest sensor measurement indicative value being thereby deleted;

(d) incrementing said buffer pointer to a next memory location of said buffer for first-in, first-out storage of-measurement values in said fixed number of memory storage locations;

(e) calculating the average of all values stored in said buffer to produce an average output value; and

(f) repeating steps (b)-(e) for each value received from said sensor.

2. The method of claim 1 wherein said sensor signal is an analog signal and said method further includes the step of converting said analog signal to a digital value prior to storing in said buffer memory.

3. The method of claim 1 wherein said sensor signal value is a measurement indicative of a sensed parameter and wherein said method further includes the step of providing means for converting said value into a calibrated reading, wherein said sensor signal value is converted into a calibrated reading prior to being stored in said buffer memory location.

4. The method of claim 3 wherein said sensor is a thermistor, said measurement is a temperature related voltage and said calibrated reading is a temperature.

5. The method of claim 4 wherein said thermistor is utilized to measure the temperature of exhaust air in a clothes dryer.

6. The method of claim 5 wherein said method is utilized to produce an average exhaust air temperature reading to control the application of heat in said clothes dryer.

7. The method of claim 1 further including the step of providing at least one additional memory storage location for storing the results of at least one intermediate calculation in calculating said average.

8. In a clothes dryer having a thermistor adapted to produce a series of voltage values each indicative of the instantaneous temperature of the exhaust air of said dryer, said thermistor being electrically coupled to a microprocessor by a transmission line and adapted to send said voltage values as an analog electrical signal to said microprocessor over said transmission line, a method of producing a series of output values accumulated during a single cycle of dryer operation and averaged to reduce the effects of electrical noise induced in said transmission line, said method comprising the steps of:

(a) producing a running average circular buffer in said microprocessor, said buffer including a fixed number of memory storage locations arranged from first to last and a pointer for indicating the next said memory location into which a value is to be stored;

(b) receiving a temperature indicating voltage value;

(c) converting said voltage value to a digital value;

(d) storing a first digital value in said buffer, said value being stored in the memory location thereof indicated by said pointer;

(e) incrementing said buffer pointer to the next memory location of said buffer, said next memory location being the first memory location when the pointer is at the last memory location for first-in, first-out storage of digital values in the buffer;

(f) storing a second digital value in the buffer in the buffer at a memory location having an oldest stored digital value stored therein, whereby the oldest stored digital value is deleted;

(g) calculating a running average of all digital values stored in said buffer to produce a running averaged output value; and

(h) repeating steps (b)-(g) for each received voltage value.

9. The method of claim 8 further including the step of converting said digital value into a calibrated temperature reading wherein said calibrated reading is stored in said buffer at said memory location indicated by said pointer.

10. The method of claim 9 wherein calibration values used to convert said temperature indicative voltage value to a calibrated temperature reading are stored in said microprocessor.