JPH0241702B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a humidity detection device that can detect humidity and dew condensation, and can extract changes in humidity and dew condensation as changes in voltage.

2. Description of the Related Art Various sensors for detecting humidity or dew condensation conditions have been proposed and implemented for various purposes. In some conventional devices, a moisture-sensitive substance is interposed between a pair of electrodes, and the state of dew condensation is detected by a sudden decrease in resistance value when condensation occurs. In addition, in other methods, conductive particles such as carbon powder are mixed with organic polymers such as epoxy, and the contact between the conductive particles is weakened due to swelling of the organic polymer during condensation, resulting in resistance. A connection condition is detected by a sudden increase in value. All of these conventional devices detect a humidity state or a dew condensation state based on a change in the resistance value of a humidity sensing element unit. Therefore, it is necessary to keep a certain amount of current flowing through the humidity sensing element unit. Therefore, if dust etc. adhere to the moisture sensing element unit,
This caused problems such as incorrect detection.

Therefore, the main object of the present invention is to provide a humidity detection device that can stably detect humidity or dew condensation based on a novel principle.

In summary, the present invention includes a semiconductor substrate that generates a thermoelectromotive force, such as a barium titanate-based semiconductor, a pair of electrodes formed on the semiconductor substrate for extracting the thermoelectromotive force, and one end side of the semiconductor substrate. The humidity sensing device includes a hygroscopic substance formed on the semiconductor substrate, a heater provided integrally with or in close proximity to the semiconductor substrate, and a control circuit including at least a circuit for intermittently applying voltage to the heater.

The above objects and other objects and features of the invention will become more apparent from the following detailed description with reference to the drawings.

FIG. 1 is an illustrative diagram showing an embodiment of the present invention. In the structure, a pair of electrodes 2 and 3 are formed at both ends of a semiconductor substrate 1 made of, for example, ferrite, barium titanate, or strontium titanate. Then, the electrode 3 of the semiconductor substrate 1
A hygroscopic substance 4 is formed on the side. As the hygroscopic substance 4, a substance is used which has the property of generating a large amount of heat of adsorption due to moisture adsorption and easily dehydrating by heating.
hygroscopic inorganic compounds such as carbon, lithium salts,
Alternatively, a mixture of a hydrophilic organic polymer film and a hygroscopic inorganic compound may be used. In addition, the semiconductor substrate 1
A metal resistance wire 5 made of nichrome or the like is arranged around the resistor wire 5 , which generates heat in response to a voltage applied from a power source (not shown) and serves to heat the semiconductor substrate 1 .
Further, lead wires 6 and 7 are connected to the pair of electrodes 2 and 3, respectively, and an output due to thermoelectromotive force generated from the semiconductor substrate 1 is taken out in a certain humidity state or dew condensation state.

The following methods are available for extracting thermoelectromotive force from the semiconductor substrate 1 based on changes in humidity and dew condensation.

One of them is to extract an output from the semiconductor substrate 1 when a voltage is applied to the heater 5. First, when a voltage is applied to the heater 5, the semiconductor substrate 1 is heated, and a temperature difference is generated between the area where the hygroscopic substance 4 is formed and the area where it is not, and an output based on thermoelectromotive force is obtained. depends on the humidity condition. Output tends to decrease as humidity increases. This is because the moisture contained in the hygroscopic substance 4 increases as the humidity increases, and even if heated by the heater 5, it becomes difficult to evaporate and the evaporation rate slows down, and heat dissipation from the semiconductor substrate 1 also decreases as the humidity increases. , the output can be detected as being smaller in high humidity or dew condensation conditions. Therefore, since the output output changes according to changes in humidity, the humidity state can be detected based on changes in the output. At this time, voltage is intermittently applied to the heater 5. This is because when a voltage is applied to the heater 5, electrons are diffused based on the temperature difference generated in the semiconductor substrate 1, which generates a thermoelectromotive force and is taken out as an output, but if the voltage continues to be applied, There is no temperature difference, and no electrons diffuse, resulting in an equilibrium state and no output. Therefore, by once ending the voltage application and applying the voltage again, the above-described operation can be repeated, and an output corresponding to the humidity state can be obtained. Note that the peak output from the semiconductor substrate 1 is taken out after applying a voltage to the heater 5.

Another method for extracting the thermoelectromotive force from the semiconductor substrate 1 is to apply a voltage to the heater 5 to heat the semiconductor substrate 1, and then extract an output based on the thermoelectromotive force generated depending on the humidity state. In other words,
When a voltage is applied to the heater 5 and the semiconductor substrate 1 is heated, moisture including the moisture in the hygroscopic substance 4 is removed. After that, the moisture contained in the surrounding atmosphere is adsorbed by the hygroscopic substance 4, and at this time, the hygroscopic substance 4
A difference in temperature occurs between the areas where the pores are formed and the areas where they are not, and an output based on thermoelectromotive force is obtained, and this output corresponds to the humidity state. If left in this state, there will be no temperature difference in the semiconductor substrate 1 itself, and no electrons will be diffused, resulting in an equilibrium state and no output will be obtained. Therefore, in this example as well, a voltage is intermittently applied to the heater 5,
After removing the moisture contained in the semiconductor substrate 1 and the hygroscopic material 4, the moisture is adsorbed on the hygroscopic material 4 again according to the humidity condition, and an output is extracted by thermoelectromotive force based on the temperature difference at that time. Just do it. Further, the output from the semiconductor substrate 1 may be set to take out the peak output as in the former case.
Furthermore, in this example, the entire semiconductor substrate 1 is heated by the heater 5.
It has been confirmed that if the heating is done equally, the change in output can be made even larger, and the change in output due to changes in humidity becomes linear.

The heater 5 is connected to a circuit that applies a voltage intermittently in order to intermittently heat the semiconductor substrate 1, and a known voltage application circuit is used for this voltage application circuit. In addition to the circuit that applies voltage to the heater 5, there is also a synchronization circuit that detects the output generated from the semiconductor substrate 1 based on the humidity state when or after applying the voltage to the heater 5. A control circuit including the circuit and an amplification detection circuit that amplifies and detects the output signal from the semiconductor substrate 1 can be incorporated into the humidity detection device. FIG. 2 shows a block diagram of an example of such a control circuit.

Next, specific examples will be described.

A flaky barium titanate semiconductor ceramic was used as the semiconductor substrate. Its size is 20mm in length and width
Using a semiconductor substrate with a diameter of 10 mm and a thickness of 0.2 mm, ohmic electrodes were provided at both ends of the semiconductor substrate, and lead wires were connected. Additionally, 30% lithium chloride was added to one end of the semiconductor substrate.
A polyvinyl alcohol film was formed. A heater was provided adjacent to this semiconductor substrate, and was set so that when a voltage was applied to the heater, the surface temperature of the semiconductor substrate was 50°C. Voltage application time to heater
A heating cycle was set for 10 seconds and the time until the next voltage application was 1 minute, and each output voltage corresponding to a relative humidity of 0 to 100% was measured.

When the output voltage due to thermoelectromotive force was measured separately during and after voltage application to the heater, results as shown in FIGS. 3 and 4 were obtained, respectively.

As is clear from FIGS. 3 and 4, the output voltage changes in response to changes in relative humidity, and changes in humidity can be electrically detected. Further, the state of change in the output voltage at 100% relative humidity is different between FIG. 3 and FIG. 4, and the output voltage can be used depending on the purpose of use.

5 to 7 show other structures of the humidity detection device according to the present invention.

In the case shown in FIG. 5, an insulating layer 8 having a thermal conductivity smaller than or equal to that of the semiconductor substrate 1, such as polytetrafluoroethylene resin, is formed on a semiconductor substrate 1 on which ohmic electrodes 2 and 3 are formed. , the semiconductor substrate 1 is made weather resistant. Furthermore, the heater 5 uses a bulk resistor instead of a metal resistance wire, and is provided close to the semiconductor substrate 1.

In the case shown in FIG. 6, a part of the heater 5 is closely attached to the semiconductor substrate 1 with an insulating layer 9 interposed therebetween.

In the one shown in FIG. 7, the heater 5 is integrally attached to the semiconductor substrate 1 with an insulating layer 9 interposed therebetween. The humidity detection device having the structure shown in FIG. 7 has the same structure as the above-mentioned embodiment,
When we measured the change in output voltage at a relative humidity of 0 to 100% after applying voltage to the heater 5, we obtained the results shown by the broken line in Figure 4, indicating that uniform heating caused a linear change in output voltage. It shows.

As described above, the output during uniform heating changes almost linearly in accordance with changes in relative humidity, but if the measured temperature changes, the characteristics shown by the broken line in FIG. 4 also change. This is because the output depends on absolute humidity.

FIGS. 8 to 10 show circuits capable of correcting such dependence of output on absolute humidity and changing the output to correspond to changes in relative humidity.

In the figure, 11 is a humidity detection device according to the present invention, 12 is a field effect transistor, and a series circuit of a resistor 13 and a thermistor 14 or a parallel circuit of this series circuit and a resistor 15 is connected to the drain side. .

Note that in the above explanation, a heater was separately provided to heat the semiconductor substrate, but if barium titanate-based semiconductor porcelain is used for the semiconductor substrate, for example, the structure can be configured to apply sufficient voltage to generate heat to the semiconductor substrate. In this way, the sensing portion can also be used as a heater.

As described above, according to the present invention, humidity changes are not detected based on resistance changes as in the past, but are detected based on thermoelectromotive force generated from a semiconductor substrate, and the output is DC. Therefore, signal processing is easy. In addition, its output signal is approximately several mV, which is larger than that of thermocouples.
Reliable detection is possible. Furthermore, only by applying a voltage to the heater intermittently can detection of the humidity state or dew condensation state be taken out as thermoelectromotive force from the semiconductor substrate, making it possible to detect humidity in immediate response to changes.

[Brief explanation of the drawing]

Fig. 1 is an illustrative diagram showing one embodiment of the present invention, Fig. 2 is a block diagram showing an example of a control circuit, and Fig. 3 is a block diagram showing an example of a control circuit.
Figure 4 shows output voltages based on specific examples.
5 to 7 are illustrative diagrams showing other embodiments of the present invention, and FIGS. 8 to 10 are diagrams showing correction circuits for the output of a semiconductor substrate. 1... Semiconductor substrate, 2, 3... Electrode, 4... Hygroscopic material, 5... Heater, 6, 7... Lead wire.

Claims (1)

[Scope of Claims] 1. A semiconductor substrate that generates a thermoelectromotive force, a pair of electrodes formed on the semiconductor substrate to extract the thermoelectromotive force, a hygroscopic substance formed on one end side of the semiconductor substrate, and a hygroscopic substance formed on one end side of the semiconductor substrate; A humidity sensing device comprising a heater provided integrally with or adjacent to a semiconductor substrate, and a control circuit including at least a circuit for intermittently applying voltage to the heater. 2. The humidity sensing device according to claim 1, wherein an insulating layer having a thermal conductivity smaller than or equal to that of the semiconductor substrate is formed on the semiconductor substrate on which the pair of electrodes for extracting thermoelectromotive force are formed. . 3. The control circuit is a patent that includes a circuit that applies voltage to the heater, a synchronization circuit that synchronizes to detect the output when voltage is applied or after voltage application, and a detection circuit that amplifies and detects the output signal from the semiconductor substrate. A humidity sensing device according to claim 1. 4. The humidity detection device according to claim 1, which detects humidity based on thermoelectromotive force generated when a semiconductor substrate is heated with a heater. 5. The humidity detection device according to claim 1, which detects humidity based on thermoelectromotive force generated after heating a semiconductor substrate with a heater. 6. The humidity detection device according to claim 5, wherein the semiconductor substrate is connected to a correction circuit that converts an output based on absolute humidity from the semiconductor substrate into relative humidity.