Compensation circuit for sensor lag to reduce undershoot and overshoot

• US 4,836,442 A
• Filed: 12/14/1988
• Issued: 06/06/1989
• Est. Priority Date: 12/14/1988
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Beckey, Thomas J.
• Primary Examiner(s): Wayner, William E.
• Application Number:
  US07/284,279
• Time in Patent Office: 174 Days
• Field of Search: 364/557, 236/46 R, 236/78 D, 236/68 B, 165/12, 374/169
• US Class Current: 236/46.00R
• CPC Class Codes: G05D 23/24 the sensing element having a resistance varying with temperature, e.g. a thermistor
• CPC Class Codes: G05D 23/275 with sensing element expanding, contracting, or fusing in response to changes of temperature

Abstract

A compensation circuit for sensor lag uses a sensor temperature signal modification circuit to provide a modified sensor temperature signal for subsequent use in controlling the sensed temperature. The compensation circuit digitally compares a current sensor temperature representative signal and a sensor temperature signal at a last or preceeding sample time to produce a difference signal which is converted to a sensor slope signal and is multiplied by a sensor time constant. The resulting signal is passed through a filter to eliminate transient effects and is summed with the original sensor temperature signal to provide a sensed temperature signal for control of the temperature whereby the sensed temperature is a better estimate of the actual environmental temperature controlled by a thermostat utilizing the sensed temperature signal.

Claims

1. A compensation circuit for a sensor lag of a sensor responsive to an environmental condition comprising

means for storing a prior output of a sensor,

means for comparing a present sensor output with the stored prior output to produce a difference output,

means for converting the difference output to a sensor slope,

means for multiplying the sensor slope by a predetermined sensor time constant,

filter means having a fixed time constant for filtering an output from said means for multiplying and

summing means for adding an output from said filter means to the present sensor output to produce a control signal for controlling the environmental condition.

2. A circuit as set forth in claim 1 wherein said means for storing includes a memory and a clock for timing the operation of said memory.

3. A circuit as set forth in claim 1 wherein said condition is temperature.

4. A circuit as set forth in claim 1 wherein said filter means includes a microprocessor programmed to produce an output according to:

space="preserve" listing-type="equation">output=(new value-old value) (1-e.sup.- time step/time constant) + old value.