Method and device for measuring humidity

• US 7,077,004 B2
• Filed: 08/02/2004
• Issued: 07/18/2006
• Est. Priority Date: 08/02/2003
• Status: Expired due to Fees

• Current Assignee: E+E Elektronik Ges.m.b.H. (Dr. Johannes Heidenhain GmbH)
• Original Assignee: E+E Elektronik Ges.m.b.H. (Dr. Johannes Heidenhain GmbH)
• Inventors: Mitter, Helmut
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): Rogers, David A.
• Application Number:
  US10/909,479
• Publication Number:
  US 20050028588A1
• Time in Patent Office: 715 Days
• Field of Search: 73/290.1, 73/290.2, 73/290.5, 73/310.5, 7333502-33505
• US Class Current: 73/335.04
• CPC Class Codes: G01N 27/223 for determining moisture content, e.g. humidity rain detectors on vehicle windows B60S1/0825

Abstract

A method and a device for measuring humidity may be suitable for determining the relative humidity in the high-humidity range. The device includes a sensor device, as well as a circuit connected to the same. The sensor device includes a capacitive humidity-sensor element, a temperature-sensor element, and a heating element, the humidity-sensor element being heated in at least one part of the humidity-measuring range. The ambient temperature is further ascertained by the circuit, from the heating power required in the heating mode, as well as from the measured, local sensor device temperature, in order to further determine the relative humidity.

Claims

1. A method for measuring humidity by a sensor device including a capacitive humidity-sensor element, a temperature-sensor element, and a heating element, comprising:

heating the humidity-sensor element in at least a part of a humidity-measuring range;

ascertaining an ambient temperature by a circuit from a heating power required in the heating step and from a measured local sensor device temperature; and

determining the relative humidity from the ambient temperature and the local sensor device temperature.

2. The method according to claim 1, wherein the relative humidity is in a range greater than 75% relative humidity.

3. The method according to claim 1, wherein the humidity-sensor element is heated in the heating step over an entire humidity-measuring range.

4. The method according to claim 1, wherein the temperature-sensor element and the heating element are integral.

5. The method according to claim 1, further comprising determining an excess temperature of the heating element resulting from the heating power, the ambient temperature ascertained in the ambient temperature ascertaining step from the heating power and the local sensor device temperature in accordance with the relationship T_a=T_s−

T_x, T_a representing the ambient temperature, T_s representing the local sensor device temperature and T_x representing the excess temperature.

6. The method according to claim 5, wherein the excess temperature determining step includes determining a corresponding measurement current by the temperature-sensor element, the excess temperature determined in the determining step in accordance with the relationship T_x=(R*TK*I²*EK);

T_x representing the excess temperature;

R representing a measured resistance of the temperature-sensor element;

TK representing a temperature coefficient of the temperature-sensor element;

I representing the measurement current through the temperature-sensor element; and

EK representing a characteristic heating coefficient of the temperature-sensor element.

7. The method according to claim 1, wherein the humidity-sensor element heating step, the ambient temperature ascertaining step and the relative humidity determining step are performed by the circuit connected to the sensor device.

8. The method according to claim 7, wherein the circuit is configured to output the ambient temperature and the relative humidity for further processing.

9. The method according to claim 1, further comprising entering a heating mode at or above a predetermined humidity limit value.

10. The method according to claim 9, wherein the humidity-sensor element is heated in the heating mode in a regulated manner to provide a constant capacitance of the humidity-sensor element.

11. The method according to claim 9, wherein the humidity-sensor element is heated in the heating mode by a heating current that increases linearly with the relative humidity.

12. A device for measuring humidity, comprising:

a sensor device including a capacitive humidity-sensor element, a temperature-sensor element and a heating element; and

a circuit configured to heat the humidity-sensor element in at least a part of a humidity-measurement range, and configured to ascertain an ambient temperature from a heating power required in a heating mode and from a measured local sensor device temperature to determine the relative humidity.

13. The device according to claim 12, wherein the device is configured to determine relative humidity in a range greater than 75% relative humidity.

14. The device according to claim 12, wherein the circuit is configured to heat the humidity-sensor element over an entire humidity-measuring range.

15. The device according to claim 12, wherein the temperature-sensor element and the heating element are integral.

16. The device according to claim 12, wherein the temperature-sensor element includes at least one resistor element, the sensor device including a carrier substrate, the capacitive humidity-sensor element and the at lest one resistor element arranged on the carrier substrate.

17. The device according to claim 16, wherein the at least one resistor element is further arranged as the heating element.

18. The device according to claim 12, wherein the circuit is connected to the sensor device and includes at least one microprocessor configured to heat the humidity-sensor element, to perform signal processing and to provide output signals.

19. The device according to claim 12, wherein the circuit is configured to operate the sensor device in the heating mode at or above a predetermined humidity limit value.

20. The device according to claim 19, wherein the circuit is configured to heat, in the heating mode, the humidity-sensor element in a regulated manner to result in a constant capacitance of the humidity-sensor element.

21. The device according to claim 19, wherein the circuit is configured to heat, in the heating mode, the humidity-sensor element by a heating current that increases linearly with the relative humidity.