Measurement method and system for humidity or gas concentration sensor

• US 20010003249A1
• Filed: 12/08/2000
• Published: 06/14/2001
• Est. Priority Date: 12/09/1999
• Status: Active Grant

• Current Assignee: Vaisala Oyj
• Original Assignee: Vaisala Oyj
• Inventors: Stormbom, Lars
• Granted Patent: US 6,564,633 B2
• Time in Patent Office: Days
• US Class Current: 73/1.06
• CPC Class Codes: G01N 27/124 varying the temperature, e.g. in a cyclic manner
• CPC Class Codes: G01N 27/223 for determining moisture content, e.g. humidity rain detectors on vehicle windows B60S1/0825

Abstract

The method and system disclosed in the publication relates to an improvement in measurement accuracy of a gas concentration sensor (1) such as capacitive humidity sensor (1), the method comprising the steps of measuring a parameter of the sensor (1), such as its resistance or capacitance, that is sensitive to the gas or its concentration being measured, and simultaneously changing the temperature of the sensor (1) in a cyclic manner. According to the invention, the parameter of the sensor (1) being measured is measured at least essentially continuously, at least N times during each heating cycle, the measured parameter value is filtered to obtain a signal component associated with the fundamental frequency of the heating cycle for use at a later step, and the thus filtered signal component is used in the correction and/or calibration of actual output signal of the sensor.

Claims

1. Measurement method for a gas concentration sensor (1) such as a capacitive humidity sensor (1), the method comprising the steps of

measuring a parameter of the sensor (1), such as its resistance or capacitance, that is sensitive to the gas or its concentration being measured,

changing the temperature of the sensor (1) in a cyclic manner, and

converting the measured value of the parameter into an actual output signal of the variable being measured, the output signal then being proportional to the measured gas concentration variable such as relative humidity, for instance,

characterized in that

the parameter of the sensor (1) being measured is measured at least essentially continuously, at least 2 times during each heating cycle,

the measured parameter value is filtered to obtain a signal component associated with the fundamental frequency of the heating cycle for use at a later step, and

the thus filtered signal component is used as the actual output signal of the sensor or, alternatively, in the correction and/or calibration of said output signal of said sensor.

2. Method according to

claim 1

, characterized in that said measured parameter value is further filtered to obtain a signal component at least essentially associated with said fundamental frequency of said heating cycle, the signal component advantageously being proportional to the concentration of the gas being measured.

3. Method according to

claim 1

or

2

, characterized in that in the method simultaneously is measured the temperature of the sensor (1) and is performed on the measurement value of the sensor temperature a filtration operation associated with the repetition rate of the heating cycle.

4. Method according to

claim 3

, characterized in that from the temperature-dependent sensor response signal is filtered a signal component at least essentially associated with said fundamental frequency of said heating cycle for further use.

5. Method according to any one of foregoing claims, characterized in that said filtration is performed using an analog technique such as a bandpass filter.

6. Method according to any one of foregoing claims, characterized in that said filtration is performed using a digital technique such as a Fourier transform analysis, for instance.

7. Method according to any one of foregoing claims, characterized in that in the method is formed the ratio of the sensor temperature value to the measurement signal value of the sensor (1) or to measurement values obtained by filtration from the measurement values of a variable computed from the sensor response.

8. Method according to any one of foregoing claims, characterized in that the value of the sensor average temperature during the heating cycle is used in the measurement of the variable being measured or in the computation of the correction term for the reading of the measurement device.

12. System according to any one of foregoing claims, characterized in that said filtration means are implemented using an analog technique such as a bandpass filter.

13. System according to any one of foregoing claims, characterized in that said filtration means are implemented using a digital technique such as a Fourier transform analysis, for instance.

14. System according to any one of foregoing claims, characterized in that the system includes means for forming the ratio of the sensor temperature value to the measurement signal value of the sensor (1) or to measurement values obtained by filtration from the measurement values of a variable computed from the sensor response.

15. Method according to any one of foregoing claims, characterized in that the system includes means for utilizing the value of the sensor average temperature during the heating cycle in the measurement of the variable being measured or in the computation of the correction term for the reading of the measurement device.

9. Measurement system for a gas concentration sensor (1) such as a relative humidity sensor, the system comprising

a gas concentration sensor (1), wherein a given parameter such as the sensor resistance or capacitance is adapted sensitive to the gas or its concentration being measured,

heating and/or cooling means (2) thermally connected to the gas concentration sensor (1),

a measurement apparatus (4) for measuring the value of a sensor parameter such as sensor resistance or capacitance that is adapted sensitive to the gas or its concentration being measured, and

means (3) for controlling cyclic heating of the sensor (1),

characterized in that

the system includes means (5) for detecting signals occurring at the fundamental frequency of said cyclic heating of the sensor.

10. System according to

claim 9

, characterized in that the system includes means for filtering said measured parameter value for further use so that the filtered signal is formed by a signal component that is at least essentially associated with said fundamental frequency of said heating cycle, the signal component advantageously being proportional to the concentration of the gas being measured.

11. System according to

claim 9

or

10

, characterized in that the system includes means for measuring essentially simultaneously the temperature of the sensor (1) and the parameter value being measured and means for filtering the temperature measurement values essentially at the fundamental frequency of the heating cycle repetition rate.