JP2011085568A - Heat-conducting moisture meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-conductive moisture meter for continuously measuring the absolute humidity, at a high speed without the use of a referencing thermistor. <P>SOLUTION: By using a sensor element, a compound nitride film material, such as a Ta-Al compound nitride, having a resistance temperature coefficient of (-)10,000 to (-)30,000 ppm/°C, is thinned, and formed on a polyimide fill substrate 11, having a heat resistance up to a temperature of 500°C and a thickness of 1-10 μm; thermal capacity is micronized; and change in the thermal conductivity of a sensor sensitive section due to the moisture contained in a gas and ambient temperature in the vicinity of a sensor are measured separately; and both the data are processed on software. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

      The present invention relates to a heat transfer moisture meter.

      As a sensor for measuring the amount of moisture contained in a gas, for example, Patent Document 1 discloses a capacitance type humidity sensor. Patent Document 2 discloses a resistance change type humidity sensor including a pair of electrodes for detecting a resistance change and a moisture sensitive film provided on the pair of electrodes. Patent Document 3 discloses a heat-conducting absolute humidity sensor using a system in which thermal resistance elements 1 and 2 for measurement and comparison are fixed.

      JP 2009-168575 A       JP 2005-291880 A       JP 07-239315 A

      Among conventional methods, a method that can directly measure the amount of water (absolute humidity) contained in a gas is a heat conduction method. The thermal conductivity type has excellent long-term stability because it does not absorb moisture. In the above-described heat conduction type absolute humidity sensor, since the platinum thin film is formed on the alumina substrate, the heat capacity of the sensor is large, and the sensor sensitivity is not sufficient in a situation where the change in the sensor resistance value is minute.

      In general, in the heat conduction type, the absolute humidity is determined by the difference in the resistance value due to the influence of moisture using a Wheatstone bridge circuit using two thermistors for moisture measurement and a reference thermistor that is not affected by moisture. It is a detection method, but it is difficult to distinguish the Wheatstone bridge circuit from the case where there is a difference between both resistance values due to factors other than the influence of moisture, such as when the amount of moisture in the measurement gas or the ambient temperature changes rapidly. There are problems such as a decrease in responsiveness due to use.

      To achieve the above object, a composite nitride material having a large resistance temperature coefficient according to claim 1 is formed on a polyimide film by thinning a composite target as a starting material by a reactive sputtering method, such as Ni or Ni and Cu. For sensors that can be energized by thin-film electrodes, the thermal conductivity change of the sensor sensitive part due to moisture contained in the gas and the ambient temperature measurement near the sensor are separately performed, and both data are processed on the software for reference It is characterized by being able to measure absolute humidity continuously at high speed without using a thermistor.

      In the heat conduction type moisture meter according to claim 2, in the heat conduction type moisture meter according to claim 1, a composite of Ta and Al whose resistance temperature coefficient of the sensor material is in the range of (-) 10000 to (-) 20000 ppm / ° C. It is characterized by being a nitride material.

      In the heat conduction type moisture meter according to claim 3, a polyimide film material having a heat resistance up to 500 ° C. having a thickness of 1 μm or more and 10 μm or less is used as a sensor substrate material in the heat conduction type moisture meter according to claim 1. And

      Among conventional humidity measuring methods, the only method that can directly measure absolute humidity is the heat conduction method. The heat conduction type is superior in long-term stability because it does not absorb moisture, but the sensor sensitivity is not sufficient in a situation where the heat capacity of the sensor is large and the change in the sensor resistance value is minute. In the present invention, a composite nitride film material having a resistance temperature coefficient of Ta and Al composite nitride material in the range of (−) 10000 to (−) 20000 ppm / ° C. is thinned to have a heat resistance of 1 to 10 μm up to 500 ° C. Sensor sensitivity and sensor responsiveness are improved by using a sensor element that is formed on a polyimide film substrate with a thickness to reduce the heat capacity, and the change in the thermal conductivity of the sensor sensitive part due to moisture contained in the gas and the vicinity of the sensor By performing ambient temperature measurement separately and processing both data on software, it is possible to provide a heat conduction type moisture meter capable of measuring absolute humidity continuously at high speed without using a thermistor for reference.

      By eliminating the reference thermistor, which is also a factor that reduces the responsiveness, the sensor size can be reduced, and the problem can be solved by taking advantage of the heat conduction type feature that can directly measure absolute humidity.

      By using a sensor material with a large temperature coefficient of resistance, it is possible to capture minute changes in thermal conductivity that are difficult to measure with conventional sensor materials such as platinum.

      By using a heat-resistant polyimide film having a thickness of 1 to 10 μm, the heat capacity of the entire heat conduction type sensor can be reduced, and the response can be improved.

      Furthermore, by improving the responsiveness, it is possible not only to display the measurement result but also to feed back the measurement result to the humidity control side and to add a control function.

    It is a block diagram of a measurement / control circuit showing an embodiment of the present invention.     It is an external view of the sensor element part which shows embodiment of this invention.     It is the figure which showed the relationship between absolute humidity and the output voltage of a moisture measurement sensor.

      Embodiments of the present invention will be described below with reference to FIGS.

      The sensor according to the present invention includes a humidity sensor that measures moisture and a temperature sensor.

      The circuit for controlling the sensor includes a circuit for driving the humidity sensor at a constant temperature and a circuit for measuring the temperature with a constant current.

      Each circuit performs temperature correction based on humidity calibration data and temperature calibration data acquired in advance during calibration.

      After performing temperature correction, it has an indicator that can calculate the absolute humidity and display the value.

      From absolute humidity, relative humidity, dew point, etc. can be calculated based on temperature data, and their values can be displayed.

      Conversion to control output based on values such as absolute humidity, relative humidity, and dew point.

      Examples of the present invention are shown below.

      Heat capacity by forming Ta and Al composite nitride film material with resistance temperature coefficient of (-) 13500ppm / ° C and Ni material for energization on 5μm thick polyimide fill substrate having heat resistance up to 500 ° C Two sensor elements with a small size were used, one of which was connected to the moisture measuring circuit and the other was connected to the temperature measuring circuit around the sensor.

      In the moisture measuring circuit, the output of the bridge circuit was adjusted so that the sensor temperature was a constant temperature of 150 ° C.

      In addition, using a standard moisture meter, the relationship between the absolute humidity and the sensor output voltage in the bridge circuit was grasped in advance and held as humidity calibration data.

      In the temperature measurement circuit, a constant current circuit to which a minute current of 10 μA was applied was formed.

      Also in the temperature measurement circuit, the relationship between the temperature and the sensor voltage was grasped in advance using a standard thermometer and held as temperature calibration data.

      The moisture measurement sensor and the temperature measurement sensor are placed in a tank capable of changing the temperature and humidity, the temperature is changed from 23 ° C. to 85 ° C., and the humidity is changed from 50% to 100% R.D. H. Until changed.

      The results are shown in FIG. A correlation between absolute humidity and sensor output voltage was obtained between 23 ° C and 85 ° C. The obtained correlation depends on temperature, and it was shown that the absolute humidity of the measurement gas can be measured by the measurement gas temperature and the output voltage of the moisture measurement sensor.

      Product reliability tests and accelerated tests are increasingly important due to widespread environmental problems. Since the present invention can continuously measure a wider range of temperature and humidity than before, it can contribute to a wide range of industrial fields.

DESCRIPTION OF SYMBOLS 1 Moisture measurement sensor 2 Constant temperature control circuit of moisture measurement sensor 3 Humidity calibration data recording circuit in moisture measurement sensor 4 Measurement gas temperature measurement sensor 5 Constant current control circuit of measurement gas temperature measurement sensor 6 Measurement gas temperature measurement sensor Temperature calibration data recording Circuit 7 Temperature correction circuit based on output voltage of moisture measurement sensor and measurement gas temperature measurement sensor and their calibration data 8 Measurement / conversion circuit for absolute humidity, dew point, etc. 9 Display section for absolute humidity, measurement gas temperature, dew point, etc. DESCRIPTION OF SYMBOLS 10 Output circuit to control based on results such as absolute humidity, dew point, etc. 11 Heat resistant polyimide film 12 Ta and Al composite nitride film material sensor sensitive part 13 Ni electrode part 14 Film sensor support

Claims (3)

In a sensor in which a composite nitride material having a large resistance temperature coefficient is thinned by a reactive sputtering method using a composite target as a starting material and formed on a polyimide film, and can be energized by a thin film electrode using Ni or Ni and Cu, Absolutely continuous at high speed without using a reference thermistor by separately measuring the thermal conductivity change of the sensor sensitive part due to moisture contained in the gas and measuring the ambient temperature in the vicinity of the sensor, and processing both data on software Heat-conducting moisture meter that can measure humidity. In the above configuration, a thermal conductivity type moisture meter characterized by being a composite nitride material of Ta and Al whose resistance temperature coefficient of the sensor material is in the range of (−) 10000 to (−) 30000 ppm / ° C. In the above configuration, a heat conductivity moisture meter using a polyimide film material having a heat resistance of up to 500 ° C. with a thickness of 1 μm to 10 μm as a sensor substrate material.