JP2017096669A - Humidity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a humidity sensor that permits heated cleaning while averting damage infliction on a temperature sensing element by dew condensation even in a highly humid environment.SOLUTION: When a heated cleaning unit 17C subjects a temperature sensing element 14 to heated cleaning, the presence or absence of dew condensation in a humidity-sensitive film 14F is determined by comparing a humidity RH measured by the temperature sensing element 14 with a reference determined value RHs preliminarily set, a normal heating characteristic A or a dew condensation-adapted heating characteristic B lower in temperature rise gradient than the normal heating characteristic A is selected according to the result of determination, and heating of the temperature sensing element with a heater is started on the basis of the selected heating characteristic.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a humidity measurement technique, and more particularly to a heat cleaning technique for cleaning a moisture sensitive element having a moisture sensitive film by heating.

  As a general humidity sensor, there is a humidity sensor that has a humidity sensing element whose element measurement value changes due to moisture contained in the moisture sensitive film, and measures ambient humidity based on the element measurement value detected from the moisture sensing element. . Since such a humidity sensor is directly exposed to the atmosphere of the measurement environment and measures humidity, gas such as moisture and chemicals / solutions in the atmosphere are sorbed to the humidity sensing element. For this reason, an error between the element measurement value of the moisture sensitive element and the initial element measurement value becomes large, and as a result, the measurement accuracy of the moisture sensitive element is lowered and further the humidity sensitive element is deteriorated.

  Conventionally, as a method of recovering such deterioration of the moisture sensitive element, a moisture sensitive element is provided by heating the moisture sensitive element by periodically driving the heater during periods other than humidity measurement. A technique has been proposed in which heat cleaning is performed to remove sorbents contained in the moisture and the deterioration of the moisture sensitive element is determined based on the difference between the measured value of the moisture sensitive element measured after the implementation and the initial value. (Refer to patent document 1 etc.). Accordingly, it is possible to suppress the progress of deterioration of the moisture sensitive element and to accurately determine whether or not the humidity sensitive element needs to be replaced due to the progress of deterioration.

Patent No. 5216442

  The humidity sensor of such a humidity sensor measures the ambient humidity based on the measured value of the element that changes depending on the moisture contained in the moisture-sensitive film. More water may be sorbed and dewed. In particular, when the humidity sensor is used in a humid environment such as a chemical atmosphere in factories or laboratories or outside air intakes, condensation tends to occur on the surface of the moisture sensitive film.

  Therefore, when condensation occurs on the surface of the moisture-sensitive film, the amount of heat generated from the heater during heat cleaning is taken away by a large amount of water sorbed on the moisture-sensitive film, so that no condensation occurs. In comparison, the temperature difference between the vicinity of the heater and the moisture sensitive film is increased. For this reason, due to the difference in coefficient of thermal expansion, a difference occurs in the amount of expansion of the constituent members constituting the humidity sensor, which may cause damage such as breakage of the constituent members and peeling between the members. There was a problem.

  An object of the present invention is to provide a humidity measurement technique capable of performing heat cleaning while avoiding damage to a moisture sensitive element due to condensation even in a humid environment.

  In order to achieve such an object, the humidity sensor according to the present invention has a humidity sensing element whose element measurement value changes according to humidity, and is based on the element measurement value detected from the humidity sensing element. A humidity sensor that measures humidity in an atmosphere, and a heater that desorbs sorbents adsorbed on the moisture sensitive element by heating the moisture sensitive element, and when the moisture sensitive element is heated and cleaned In addition, the humidity measured by the moisture sensitive element is compared with a reference determination value set in advance to determine the presence or absence of condensation on the moisture sensitive film, and in accordance with the determination result, it is compared with the normal heating characteristic or the normal heating characteristic. And a heating cleaning unit that selects a dew condensation heating characteristic having a gentle temperature rise gradient and starts heating the moisture sensitive element by the heater based on the selected heating characteristic.

  Further, in one configuration example of the humidity sensor according to the present invention, after the heating cleaning unit starts heating the moisture sensitive element by the heater, the element measurement value indicates a predetermined tolerance indicating that the moisture sensitive performance is restored. The heating by the heater is stopped when the arrival confirmation is confirmed to have reached the range.

  According to the present invention, when there is condensation on the moisture sensitive film, the moisture sensitive element is heated based on the heating characteristic B for condensation when the temperature rise gradient is gentle. For this reason, the moisture sensitive film surface temperature can be raised without much delay with respect to the rise in the heater vicinity temperature, and the temperature difference between the two can be kept small. Therefore, even in a humid environment, heat cleaning can be performed while avoiding damage to the moisture sensitive element due to condensation.

It is a block diagram which shows the structure of a humidity sensor. It is a structural example of a moisture sensitive element. It is a flowchart which shows the heat cleaning process with respect to a moisture sensitive element. It is explanatory drawing which shows the temperature change in a moisture sensitive element by heater heating. It is explanatory drawing which shows applied voltage control. It is explanatory drawing which shows duty ratio control. It is explanatory drawing which shows applied voltage and duty ratio control.

Next, an embodiment of the present invention will be described with reference to the drawings.
First, a humidity sensor 10 according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing the configuration of the humidity sensor.

  This humidity sensor 10 has a humidity sensitive element whose element measurement value changes due to moisture contained in the moisture sensitive film, and has a function of measuring ambient humidity based on the element measurement value detected from the moisture sensitive element. Yes. For example, the humidity sensor 10 is used when measuring humidity by being directly exposed to the atmosphere of a measurement environment in the manufacturing process of various articles. At this time, a gas composed of moisture, chemicals, and solutions in the atmosphere, for example, a gas of an organic solvent such as methanol, ethanol, propanol, and acetone, is sorbed on the moisture sensitive element. For this reason, it has a function of desorbing the sorbed material adsorbed on the moisture sensitive element by heating and cleaning the moisture sensitive element.

  The humidity sensor 10 includes a communication I / F unit 11, an operation input unit 12, a display unit 13, a humidity sensor 14, a temperature sensor 15, a heater 16, and a control unit 17 as main function units. . The communication I / F unit 11 performs data communication with an external device such as an industrial controller connected via a communication line, so that a setting instruction, a measurement instruction, a heating cleaning instruction, and a humidity measurement result regarding humidity measurement are performed. It has a function of exchanging various data such as deterioration diagnosis results.

The operation input unit 12 includes an operation input device such as a button or a switch, and has a function of detecting an operation of the operator and outputting the operation to the control unit 17.
The display unit 13 includes a display device such as an LCD or an LED, and has a function of displaying various data such as setting contents related to humidity measurement, a humidity measurement result, and a deterioration diagnosis result.

  The moisture sensitive element 14 is an element whose element measurement value (element capacitance value) C changes due to moisture contained in the moisture sensitive film. FIG. 2 is a configuration example of the moisture sensitive element, FIG. 2A is a top view of the moisture sensitive element, and FIG. 2B is a front view of the moisture sensitive element. In addition, FIG. 2 is one structural example of a moisture sensitive element, and is not limited to this structural example.

  The moisture sensitive element 14 includes a first detection electrode 14E formed on the surface of the substrate 14B and a moisture sensitive film made of a polymer material having a specific cross-linked structure formed on the upper surface of the detection electrode 14E. 14F and a second detection electrode 14E formed on the upper surface of the moisture sensitive film 14F. That is, the two detection electrodes 14E are opposed to each other with the moisture sensitive film 14F interposed therebetween. These detection electrodes 14E are connected to the control unit 17 via lead wires L1 connected to pads 14P formed at the respective end points, and the detection electrodes 14E that change according to the moisture contained in the moisture sensitive film 14F. The element measurement value C in between is detected by the humidity measuring unit 17A and converted into humidity.

  A temperature sensing element 15 made of a resistance temperature detector is disposed on the back surface of the substrate 14B opposite to the detection electrode 14E, and is connected to the control unit 17 via a lead wire L2 connected to the pad 14P. The resistance value of the resistance temperature detector that changes in accordance with the temperature is detected by the control unit 17 and converted into the element temperature T of the humidity sensing element 14. The temperature sensing element 15 operates as a heater 16 that generates heat by the drive current supplied from the control unit 17 via the lead wire L2, and heat-cleans the moisture sensitive film 14F of the humidity sensing element 14 by heat generation.

  The control unit 17 includes a control circuit having a CPU and its peripheral circuits, and has a function of controlling a humidity measurement operation and a heating cleaning operation in the humidity sensor 10. The control unit 17 is provided with a humidity measurement unit 17A, a temperature measurement unit 17B, and a heat cleaning unit 17C as main processing units.

  The humidity measuring unit 17A converts the element measurement value C of the moisture sensitive element 14 detected via the lead wire L1 into humidity based on a preset function equation, thereby surrounding humidity including the moisture sensitive element 14 (Relative humidity) It has a function to measure RH and a function to display and output a measurement result on the display unit 13 or to an external device via the communication I / F unit 11.

  The temperature measurement unit 17B measures the element temperature T of the moisture sensitive element 14 by converting the resistance value of the temperature sensitive element 15 detected via the lead wire L2 into a temperature based on a preset function equation. It has a function.

  The heat cleaning unit 17C compares the humidity (relative humidity) RH measured by the humidity measurement unit 17A with the reference value RHs set in advance when the humidity measurement unit 17A starts the heat cleaning of the humidity sensor 14. The function of determining the presence or absence of condensation on the moisture-sensitive film, and when RH <RHs and it is determined that there is no condensation, normally heating characteristic A is selected, and when RH ≧ RHs and it is determined that condensation is present It has a function of selecting the dew condensation heating characteristic B, which has a gentler temperature rise gradient than the normal heating characteristic A.

  Further, the heating cleaning unit 17C drives the heater 16 based on the selected heating characteristics to start heating the moisture sensitive element 14, and after the heating is started, the element measurement value C indicates the recovery of the moisture sensitive performance. It has a function of stopping the heating by the heater 16 when it is confirmed that it has reached the predetermined allowable range Ca.

[Operation of this embodiment]
Next, the operation of the humidity sensor 10 according to the present embodiment will be described with reference to FIG. FIG. 3 is a flowchart showing a heat cleaning process for the moisture sensitive element.
The heat cleaning unit 17C of the control unit 17 performs the heat cleaning process of FIG. 3 periodically or in response to an instruction from the communication I / F unit 11 or the operation input unit 12.

  First, the heat cleaning unit 17C acquires the humidity (relative humidity) RH measured by the humidity sensing element 14 from the humidity measurement unit 17A when starting the heat cleaning of the humidity sensing element 14 (step 100), and sets the humidity RH in advance. By comparing with a set reference determination value RHs, the presence or absence of condensation on the moisture sensitive film is determined (step 101).

Here, when it is determined that RH <RHs and there is no condensation (step 101: YES), a preset normal heating characteristic A is selected (step 102), and RH ≧ RHs and it is determined that there is condensation. If it has been performed (step 101: NO), the preset condensation characteristic B is selected (step 103).
Thereafter, the heat cleaning unit 17C drives the heater 16 based on the selected heating characteristic to start heating the moisture sensitive element 14 (step 104).

  FIG. 4 is an explanatory diagram showing a temperature change in the moisture sensitive element due to heater heating. In FIG. 4A, the heating characteristic A is a normal heating characteristic, and is a heating profile that increases the heater vicinity temperature Th in the vicinity of the heater 16 from the temperature Tc1 to the temperature Tc2 over time t1. Further, the temperature characteristic 41 shows the temperature change of the moisture sensitive film surface temperature Tf on the surface of the moisture sensitive film 14F when there is no condensation, and the temperature characteristic 42 shows the temperature change of Tf when there is condensation. Tc1 is a normal temperature, and Tc2 is a temperature required to desorb the sorbed material adsorbed on the moisture sensitive element 14.

  When there is no condensation, the heat dissipation effect on the moisture sensitive film 14F side is small. For this reason, even if the heater 16 is heated at a steep temperature increase gradient like the normal heating characteristic A, Tf can be increased without much delay with respect to the increase in Th as in the temperature characteristic 41. Therefore, the temperature difference ΔTa between Th and Tf is relatively small.

  On the other hand, when the water droplet W adheres to the surface of the moisture sensitive film 14F and is condensed, the heat radiation effect on the moisture sensitive film 14F side is great due to the heat of vaporization of the water droplet W. For this reason, when the heater 16 is heated with a steep temperature rise gradient like the normal heating characteristic A, Tf rises with a large delay with respect to the increase in Th as in the temperature characteristic 42. Therefore, since the temperature difference ΔTb between Th and Tf becomes large, a difference occurs in the amount of expansion of the constituent member of the moisture sensitive element 14 due to the difference in thermal expansion coefficient between them, and the constituent member is damaged or the member There is a risk of damage such as peeling.

  On the other hand, in FIG. 4B, the heating characteristic B is a normal heating characteristic, and is a heating profile that requires a time t2 longer than T1 and raises the heater vicinity temperature Th from the temperature Tc1 to the temperature Tc2. Further, the temperature characteristic 43 shows the temperature change of the moisture sensitive film surface temperature Tf when there is no condensation, and the temperature characteristic 44 shows the temperature change of Tf when there is condensation.

  When there is no condensation, the heat dissipation effect on the moisture sensitive film 14F side is small. For this reason, when the heater 16 is heated at a gradual temperature increase gradient as in the dew condensation heating characteristic B, the Tf can increase without much delay with respect to the increase in Th as in the temperature characteristic 43. Therefore, like the temperature characteristic 41, the temperature difference ΔTa between Th and Tf is relatively small.

  On the other hand, when the water droplet W adheres to the surface of the moisture sensitive film 14F and is condensed, the heat radiation effect on the moisture sensitive film 14F side is great due to the heat of vaporization of the water droplet W. At this time, when the heater 16 is heated at a gentle temperature rise gradient as in the dew condensation heating characteristic B, the Tf can rise without much delay with respect to the increase in Th as in the temperature characteristic 44. Therefore, since the temperature difference ΔTb between Th and Tf remains relatively small, damage due to the difference in thermal expansion coefficient can be avoided.

After starting heating in this way, the heating cleaning unit 17C monitors the transition of the element measurement value C sequentially measured by the humidity measurement unit 17A (step 105).
Here, until the element measurement value C reaches the predetermined allowable range Ca indicating the recovery of the moisture sensitive performance (step 105: NO), the heating of the moisture sensitive element 14 is continued, and when C reaches the Ca. (Step 105: YES), the heating by the heater 16 is stopped (Step 106), and the series of heating cleaning processes is terminated.

  Regarding the heating characteristic B for dew condensation, a characteristic curve that does not cause damage may be specified empirically by repeating the test. In addition, based on the coefficient of thermal expansion of each member constituting the moisture sensitive element 14, the size and bending strength of the member, the fixing strength between the members, etc., the temperature difference between Th and Tf is specified as a safe temperature difference that does not cause damage. Then, the dew condensation heating characteristic B may be specified such that the temperature difference between Th and Tf is kept below this safe temperature difference.

Further, as a method of realizing the normal heating characteristic A and the dew condensation heating characteristic B, the applied voltage used for driving the heater 16, the duty ratio, or a combination thereof may be adjusted.
FIG. 5 is an explanatory diagram showing applied voltage control. Here, a method of driving the heater 16 with the applied voltage Va in the case of the normal heating characteristic A and a method of driving the heater 16 with the applied voltage Vb lower than the applied voltage Va in the case of the heating characteristic B for dew condensation is shown. Has been.

FIG. 6 is an explanatory diagram showing duty ratio control. Here, a method is shown in which the pulse width with respect to the drive pulse period ts is set to tpa in the case of the normal heating characteristic A, and the pulse width tpb is shorter than tpa in the case of the heating characteristic B for condensation.
FIG. 7 is an explanatory diagram showing applied voltage / duty ratio control. Here, in the case of the normal heating characteristic A, driving is performed with a driving pulse having a pulse width tpa with the applied voltage Va, and in the case of the heating characteristic B for dew condensation, driving with a pulse width ttpb shorter than tpa with an applied voltage Vb lower than Va. A method of setting a pulse width tpb shorter than the driving tpa by a pulse is shown.

[Effects of the present embodiment]
As described above, in the present embodiment, the heat cleaning unit 17C compares the humidity RH measured by the moisture sensitive element 14 with the preset reference determination value RHs when the moisture sensitive element 14 is heated and cleaned. The presence or absence of condensation on the wet film 14F is determined, and the normal heating characteristic A set in advance according to the determination result, or the heating characteristic B for dew condensation having a gentler temperature rise than the normal heating characteristic A is selected. Then, heating of the moisture sensitive element 14 by the heater 16 is started based on the selected heating characteristic.

  Thereby, when there is dew condensation on the moisture sensitive film 14F, the moisture sensitive element 14 is heated based on the dew condensation heating characteristic B having a gentle temperature rise gradient. For this reason, the moisture sensitive film surface temperature Tf can be raised without much delay with respect to the rise in the heater vicinity temperature Th, and the temperature difference between the two can be kept small. Therefore, even in a humid environment, heat cleaning can be performed while avoiding damage to the moisture sensitive element 14 due to condensation.

Further, in the present embodiment, after the heating cleaning unit 17C starts to heat the moisture sensitive element 14 by the heater 16, the element measurement value C has reached a predetermined allowable range Ca indicating the recovery of the moisture sensitive performance. When the arrival confirmation is confirmed, the heating by the heater 16 may be stopped.
Thereby, the sorbent contained in the moisture sensitive element 14 can be reliably removed as compared with the case where the heater is periodically driven during a period other than humidity measurement to heat-clean the moisture sensitive element 14. .

[Extended embodiment]
The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. In addition, each embodiment can be implemented in any combination within a consistent range.

  DESCRIPTION OF SYMBOLS 10 ... Humidity sensor, 11 ... Communication I / F part, 12 ... Operation input part, 13 ... Display part, 14 ... Humidity sensitive element, 14B ... Substrate, 14E ... Detection electrode, 14F ... Humidity sensitive film, 14P ... Pad, 15 DESCRIPTION OF SYMBOLS ... Temperature sensor, 16 ... Heater, 17 ... Control part, 17A ... Humidity measurement part, 17B ... Temperature measurement part, 17C ... Heat cleaning part, L1, L2 ... Lead wire, C ... Element measurement value, Ca ... Permissible range, RH ... humidity, RHs ... reference judgment value, T ... element temperature, Th ... heater vicinity temperature, Tf ... moisture sensitive film surface temperature, A ... normal heating characteristics, B ... heating characteristics during condensation.

Claims (2)

A humidity sensor that has a humidity sensing element whose element measurement value changes according to humidity and measures humidity in a measurement environment atmosphere based on the element measurement value detected from the humidity sensing element,
A heater that desorbs the sorbent adsorbed on the moisture sensitive element by heating the moisture sensitive element;
When heat-cleaning the moisture-sensitive element, the humidity measured by the moisture-sensitive element is compared with a preset reference determination value to determine the presence or absence of condensation on the moisture-sensitive film, and normal heating is performed according to the determination result. A heating cleaning unit that selects a heating characteristic for dew condensation that has a gentler temperature rise compared to the normal heating characteristic, and starts heating the moisture sensitive element by the heater based on the selected heating characteristic. A humidity sensor characterized by that. The humidity sensor according to claim 1,
The heating cleaning unit, after starting to heat the moisture sensitive element by the heater, at an arrival confirmation time when it is confirmed that the element measurement value has reached a predetermined allowable range indicating recovery of moisture sensitive performance, A humidity sensor, wherein heating by the heater is stopped.

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