Circuit arrangement for correction of a sensor output

• US 4,499,423 A
• Filed: 12/08/1981
• Issued: 02/12/1985
• Est. Priority Date: 12/18/1980
• Status: Expired due to Fees

• Current Assignee: Dragerwerk AG
• Original Assignee: Dragerwerk AG
• Inventors: Matthiessen, Hans
• Primary Examiner(s): Levy, Stewart J.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/328,506
• Time in Patent Office: 1,162 Days
• Field of Search: 307/492, 328/145, 324/425, 324/438, 324/439, 324/71.1, 324/132, 324/140 R, 324/166, 324/225, 364/573, 364/571, 204/406, 204/432, 73/23, 73/29
• US Class Current: 324/425
• CPC Class Codes: G01D 3/02 with provision for altering or correcting the law of variation
• CPC Class Codes: G01N 27/4045 for gases other than oxygen

Abstract

A circuit arrangement is disclosed for correcting the output of a sensor which experiences changes in sensitivity due to the presence of one or more influencing factors, such as the concentration of a material to be sensed, or the passage of time. The circuit arrangement includes a correction network which generates a simulated sensitivity curve which simulated curve is combined with the output of the signal to produce a corrected output signal which has apparent constant sensitivity.

Claims

1. A circuit arrangement for correcting the output of a sensor which experiences time dependent error changes in sensitivity, according to a sensitivity curve, as a function of at least one influence factor comprising:

correction circuit means which simulates the sensitivity curve as a function of time and the at least one influence factor, connected to the sensor for receiving the sensor output and for producing from the sensor output a corrected output signal of constant sensitivity, said correction circuit means comprising a differential amplifier having two inputs and an output, one of said inputs being provided with a value corresponding to a sensitivity of the sensor when it is not experiencing a load, the other input provided for receiving a quantity proportional to the sensor output as it is changed according to the sensitivity curve.

2. A circuit arrangement according to claim 1, wherein said correction circuit means includes a digital circuit for simulating the sensitivity curve.

3. A circuit arrangement according to claim 1, wherein said correction circuit means includes at least one RC element for generating a logarithmic simulated sensitivity curve which corresponds to logarithmic sections of the sensitivity curve of the sensor.

4. A circuit arrangement according to claim 1, wherein the sensor comprises an electro-chemical sensor for determining alcohol concentration in a gas mixture, the sensitivity curve changing as a function of time and an occuring concentration value of alcohol in the gas mixture, said correction circuit means including means for readjusting a gain of a measuring amplifier for receiving an input quantity occurring as a voltage drop at a load resistance in the circuit of the electro-chemical cell.

5. A method of correcting the output of a sensor which experiences a change in sensitivity that changes in time to a known extent as a function of at least one influence factor comprising:

generating a simulated sensitivity curve which simulates the changing sensitivity with time and as a function of the at least one influence factor;

combining a value from the sensitivity curve with an actual output value from the sensor at each point in time plotted on the curve to generate a corrected output signal; and

providing the corrected output signal as an indicating output of the sensor.