JPS6347644A - Moisture detector - Google Patents

Abstract

PURPOSE:To simplify the detection of moisture and to achieve cost reduction, by enclosing a heater and a temp. sensor in a cylindrical container made of a metal and plastic and discharging heat from the heater pulsatively and measuring the change in the quantity of heat in the container by the sensor. CONSTITUTION:A cylindrical container closed at one end thereof is divided into a metal part 3 and a plastic part 4, and a heater 1 and a temp. sensor 2 are fixed to the container so as to be brought into contact with the metal part 3 and a lead wire is drawn out from the other end of the container. The container is inserted in a water absorbing and holding material and the heater 1 is operated only for several min to measure the quantity of heat received by the sensor 2 as output voltage. Said heat is also simultaneously escaped to the water absorbing and holding material in contact with the metal part 3 and the heat remaining in the metal part 3 imparts change to the sensor 2. Therefore, by measuring the change in the output voltage of the sensor 2, water content can be detected and, when the sensitivity or the position of the sensor 2 is changed, this detector can correspond to the change in water content. By this method, a structure can be made simple and inexpensive.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a moisture sensor and its measuring device.
The purpose of this device is to simplify and miniaturize the sensor section and measurement control section and reduce production costs so that the moisture content of moisture retaining materials such as rock wool used in greenhouse horticulture can be easily measured. .

A known prior art moisture sensor based on the same principle as the present invention is a self-recording specific heat type soil moisture monitoring system (developed by the Agricultural Research Institute of the Ministry of Agriculture, Forestry and Fisheries).

An infrared moisture sensor (manufactured by Hitachi) is different in principle from the moisture sensor of the present invention.

Problems to be Solved by the Invention However, conventional moisture sensors have very complex and elaborate structures due to differences in purpose of use, and the part that detects and controls the sensor output is difficult to solve. The moisture meter has also become large and complicated, and must be used in a fixed position, making it impossible to move the moisture meter to measure moisture.

In addition, the cost was naturally high, so we designed it to be easy to use for greenhouse horticulture, general agriculture, home gardening, and other purposes, and to be portable.0 The principle of measuring moisture with a moisture sensor is as follows. When a heat source and a temperature sensor are connected through a thermal conductor, the amount of heat released in pulses from the heat source is transferred to the substance that is in contact with the thermal conductor, and the heat remaining inside the conductor changes to the temperature sensor. give.

Based on this principle, an example of measuring moisture in a rock wool water absorbing and retaining material using a sensor equipped with a resistance temperature sensor and a platinum coil heating element is shown in FIG.

Columns A (1) to (8) in FIG. 1 are a schematic representation of the principle of the temperature sensor. 1 is a B degree sensor, 2 is a heat source, and 3 is a heat conductor. A tsuba with good thermal conductivity was used.

Columns (1) to (8) in FIG. 1B are diagrams showing output patterns corresponding to the humidity sensors in columns 0 to B.

The structure shown in Figure 1 (1) K is suitable for measuring relatively low water content, and the structure shown in (2) is suitable for measuring medium (average) water content. ing. Furthermore, the structure shown in (3) is suitable for measuring high water content where sensitivity is difficult to obtain.

In the humidity sensor having the above structure, in order to minimize the influence of external heat changes, it is necessary to provide a compensating temperature sensor at a position where heat does not pass through the thermal conductor.

Also, if the heat source is continuously generated, thermal equilibrium will naturally occur in the conductor and no change in output will appear, so until the heat in the conductor is completely dissipated and the temperature approaches the original temperature of the object to be measured. The next measurement cannot be made, and if the measurement is made before the temperature of the object to be measured returns to the original temperature, the measurement error will increase.

Means for Solving the Problems The present invention provides a thermal conduction moisture sensor having the structure shown in FIGS. 2(a), (b), and (C) using a platinum thin film resistance temperature sensor. There is something to do.

Another object of the present invention is to provide a thermally conductive moisture sensor having the structure shown in FIG. 2(d) using a thermocouple temperature sensor.

Furthermore, the present invention provides a circuit for operating the moisture sensor and a detection control circuit for displaying the sensor output.
This invention relates to a portable moisture meter characterized by having the circuit configuration shown in FIG.

The moisture sensor K (consisting of a sensor section and a detection control section) of the present invention will be explained below with reference to the accompanying drawings.

The sensor part is shown in Figure 2 (a), (b), (C) and (d).
) has the structure shown below. (a), (b), (C) above
This is done with ease of use in mind! ＞ , (d)
This is based on consideration of moisture sensing accuracy.

The sensors in FIGS. 2(a), (b), and (C) are cylindrical in shape with an outer diameter of approximately 6 mm and a length of approximately 70 fi. The cylinder is divided into a metal part 3 made of copper or the like and a plastic part 4 made of Duracon resin or the like. Inside thereof, a heater part 1 is fixed in contact with the metal part 3, and a temperature sensor (2-1) such as a platinum film resistor is fixed at a constant distance from the heater part 1 using a thermally conductive adhesive.

Furthermore, another identical temperature sensor is fixed as a reference temperature sensor (2-2) at a position where it can block the heat from the heater section 1.

In the sensors shown in FIGS. 2(a), (b) and (C), 5 is a lead wire and 6 is a rubber cap.

Figure 2: Sensors with structure (2) focus on stability of performance, sensors with structure (b) focus on average performance and ease of manufacture, and sensors with structure (C). Each type has its own characteristics, each with improved accuracy in the high-concentration moisture range.

Next, the sensor with the structure shown in FIG. 2(d) has a bottle opener shape, and the sensor part has a diameter of 5fi at its tip.
It has the shape of a square bar with a length of 40w1. Inside, a heat-resistant resin pipe 9 is passed through so that the heat-sensitive part of the thermocouple 7 is placed in the center, and a nichrome wire is inserted from the top of the resin pipe 9 over a length of about 40 cm. A coil heater 1 such as the one above is being heated in the spring. A water-resistant resin 9 is coated thereon.

Further, the same thermocouple 8 as a reference temperature sensor is housed in the same resin vibrator 9 as the sensor part inside the lead wire part 10-2001 away from the sensor part.

The basic circuit of the sensor shown in Fig. 2 is shown in Fig. 2(a), (
b), [C) When a resistive temperature sensor is used as the temperature sensor having the structure shown in K, a bridge circuit as shown in FIG. 3 (1) is used.

On the other hand, when a thermocouple type temperature sensor is used as the temperature sensor having the structure shown in FIG. 2(d), a circuit as shown in FIG. 3(11) is used.

In Fig. 3 and H, the circuit current is caused to flow with a voltage of about 2V from E (power source), and the zero output position is determined. The heater (H) is made to generate several watts of heat for only several tens of seconds to several minutes, and the heat received by the temperature sensor (S) at that time is measured by the sensor output voltage (Vout). Figure 3 ■ requires power only for the heater.

In Figure 3, 几 is a control temperature sensor, SC is a thermocouple, S
Cr is a control thermocouple.

Note that in FIG. 2(d), the reference temperature sensor 8 can be omitted, but it is necessary to use a temperature compensating lead wire for connecting the sensor section to the detection control section. The basic circuit in this case is shown in Figure 3 (Ii [) K
show.

<II) Detection Control Section Next, the configuration of the detection control section of the sensor shown in FIGS. 2(a), (b), (c), and (d) will be explained with reference to FIG. 4.

In Fig. 4, in the IA, 1 is a measurement start switch, 2 is a sensor section, 3 is a zero potential hold circuit for initial value reading υ, 4 is a sample value hold circuit that holds VOut, and 5 is a sample value hold circuit that holds Vout. A circuit that converts and displays the water content, 6 a circuit that takes out the held Voli as an external signal, 7 a storage battery type power supply circuit, and a timer T.
, , T, , T, and T4 are for sequentially operating the circuits (1) to (6). The weight of the detection control section is about 1 kg.

The configuration of the detection control section of the sensor with the structure shown in FIG. 2(d) is the same as that shown in FIG. 4, but there are slight differences in the power supply circuit and signal processing section, so the types are separated. .

The operating state of the block diagram of FIG. 4 is shown in FIG. 5 by a signal diagram.

In Figure 5, 1 is the sensor output voltage (Vout)
(mV) % zero potential volt time (seconds), 3 is sample value halt time M (seconds), 4 is restart signal, T.

~T4? 'i delay time (seconds).

As shown in FIG. 6A and B, insert the sensor into a position that is considered suitable for measuring a sample such as rock wool, which is a water absorption and retention material, until the sensor part is hidden, and connect the sensor lead wire to the detection control part. Preparations for moisture measurement are completed.

Next, the measurement conditions are determined using the actuation signal patterns shown in Fig. 6A and B and Fig. 5.
This will be explained with reference to the circuit configuration diagram shown in the figure.

When the start switch 1 is pressed, the zero potential halt circuit 3 and the timer T are activated. From that point on, preparations to read the sensor output value (Vout) are completed, and the timer T
, Approximately 3 seconds after K, the sensor heater circuit (2), timer T, and timer T are activated. The heater begins to heat up, and the heat is transferred to the sensor section in Figures 2 (a) and (b).
, (C) is a metal tube, Figure 2 (d) -1? begins to be transmitted to the heater and temperature sensor through the resin pipe. However, heat also escapes to the water-containing material that is in close contact with the sensor part, so if the thermal conductivity of the water-absorbing material is sufficiently low, the amount of water contained in the material The amount of heat escaping to changes. Therefore, the amount of heat received by the temperature sensor is large when the water content is relatively low, and small when it is large. The output state of the sensor is shown by curve 1 in FIG.

Timer T2 stops sensor heater circuit 2 and zero potential hold circuit 3 within a few minutes.

Timer T expires just before timer T2 expires, and the sample value is held! Activate 4. The sample value hold circuit immediately holds Vout immediately before the heater is turned off and sends it to the next display circuit 5.

The display circuit 5 converts Vout into water content using the first corrected coefficient and displays it. The output number output circuit 6 is a circuit for continuously outputting Vout.

The timer T4 operates at the same time as the timer T2 goes off, and after an arbitrarily set time, the timer T4 is operated to automatically measure the water content over time, and the minimum value of the time interval is approximately It takes more than 5 minutes. Also, when measuring at any time, it is possible to use the start switch IK. In this way, the water content can only be measured in pulses, but since the displayed value of the previous pulse is held until a new pulse is input, it is possible to measure continuously in steps.

Next, Figure 2 (a) shows the relationship between the sensor output when the water content in rock wool (manufactured by Grodan) is forcibly changed.
) is shown in FIG. 7, and the sensor shown in FIG. 2 ((1) is shown in FIG. 8).

The measurement conditions for the sensor shown in Figure 2 (a) are: the time required for one measurement is 1 minute, the heater power is 0.8 W (for 1 minute only), and the sensor output is the number of outputs shown in Figure 4 (6). Direct reading of the circuit output and volumetric moisture content of 100% is when measuring rock wool by placing it in water. .

The measurement conditions for the sensor shown in Figure 2(d) are: no reference thermocouple is used, the electromotive force output is from the temperature sensor alone, the heater power is approximately o, 9W, and the time taken for one measurement tcy. It is 3 minutes. The measured value is 800% of the actual electromotive force output value.
This is a value that has been expanded twice.

EXAMPLES Next, the present invention will be explained with reference to examples, but the present invention is not limited thereto.

Example Using the sensor shown in Fig. 2(b), the inner diameter 1 was measured in a greenhouse.
Fill a small plastic pot with a height of 12crIL with fine grains of dry black soil, insert it into the center of the pot until the sensor part is covered (approximately 73mm from the top of the soil to the tip of the sensor), and saturate the soil with water until water collects. After setting that point as 100 and measuring the weight of water, the measurement was started. Measurements were continuously recorded by connecting a recorder to the output count circuit.

The measurement interval was every 30 minutes (however, the total weight of water in the saturated state was 323 mm, and the internal volume of the pot was 600 mm).

In Figure 9, after about two weeks of measurement, the moisture content decreased to 30% (about 97 g) at the edge, and the output value (Vout)
initially varied from 5.9 mV to 9.7 mV. Beyond that, the amount of moisture decrease was very slight and the amount of change was also slight. The amount of change shows that there is a correlation, and measurement is possible in high moisture areas.

Effect of the invention According to the present invention, the following effects can be obtained.

1) The sensor structure is simple and inexpensive, and the sensor can be easily replaced and connected, so the number of measurement points can be increased.

2) Measurement accuracy can be improved by changing the sensor model used.

3) As a moisture meter, it is small and lightweight and can be carried and used, and the moisture content can be directly connected.

4) Moisture content can be measured in about 1 minute.

5) By changing the calibration value, it can be used for rock cool, soil, and other hydrated substances into which a sensor can be inserted, and can also be used in the field of food containing moisture.

6) Other applications include a simplified version of this device that can automatically water bonsai and lawns.

[Brief explanation of the drawing]

Fig. 1 A (1) to (3) are schematic diagrams for explaining the principle of the humidity sensor, Fig. 1 B (1) to (3) are its output pattern diagrams, and Fig. 2 (a), ( b), (C) and (d) are diagrams showing the structure of the humidity sensor of the present invention, Figures 3 (1), (If) and (II are basic moisture detection circuit diagrams, and Figure 4 is a diagram showing the structure of the humidity sensor of the present invention. FIG. 5 is a block diagram showing the operating state of the moisture detector; FIG. 5 is a signal diagram showing the operating state of the moisture detector of the present invention; FIG. 6A is a schematic diagram showing the state of measuring water content; FIG. Figure 6A is a sectional view, Figure 7 is a temperature resistance type sensor of the present invention (Figure 2(a)
Figure 8 shows the relationship between the volumetric moisture content (conversion) and the output change (mV) according to the structure shown in Figure 2(d). Volumetric moisture content (%) and output change due to (
Figure 9 shows an example of moisture measurement in soil using the thermocouple sensor of the present invention [with the structure shown in Figure 2 (b)]. It is a figure showing the relationship between (%) and the number of elapsed days (days). In Fig. 1, 1...Temperature sensor, 2...Heat source, 3...Heat conductor, In Fig. 2, 1...Heater, 2...Temperature sensor, 3...Full wing , 4...Plastic, 5...Lead wire, 6...
・Rubber cap, 7... Thermocouple, 8... Control thermocouple, 9... Resin cap, 10... Water resistant resin In Figure 3, E... Power supply, H... Heater , S...temperature sensor, R...control temperature sensor, Sc...thermocouple,
Sar... Temperature sensor for reference Figure 4: 1... Start switch, 2... Sensor circuit, 3
...Zero potential hold circuit, 4...Sample value hold circuit, 5...Display circuit, 6...Output number display circuit, 7...Power supply circuit, T, ~T4...Timer circuit In FIG. 5, 1... sensor output voltage (Vout), 2...
Zero potential hold time, 3... Sample value hold time, 4... Restart signal, T, ~T4... Delay time In Figure 6, 1... Temperature resistance type sensor, 2... Thermoelectric sensor Paired sensor-13: Rock wool water absorption and retention material. Agent Masao Miyake and 1 other person Figure 1 (A) (B) Volumetric water content (%) Volumetric water content $ (%) Volumetric water content (%) Figure 2 Figure 3 (I) (n) (III ) Figure 4 Figure 5 Time (seconds) Figure 6 A Procedural amendment (as of October 16, 1986)

Claims (2)

[Claims] (1) A metal part 3 is placed inside a long and narrow container that is closed at one end.
and a plastic part 4, and a heater part 1 in contact with the metal part 3, and a temperature sensor 2 of a platinum film resistance type or a thermocouple type at a certain distance from the metal part 3 with a thermally conductive adhesive.
Furthermore, another identical temperature sensor 2 is installed as a control temperature sensor in the same container at a position where it can block the heat from the heater part 1, and the lead wires of the heater and temperature sensor are connected to the other end of the container. A moisture detector characterized by having a drawer section. (2) In the hollow container in the shape of a bottle opener, a thermocouple 7 is installed inside the hollow heat-resistant resin pipe 9 at the head, and a heater 1 is installed outside the pipe 9. Furthermore, the heater 1 is coated with a water-resistant resin 10, and the same thermocouple 8 as described above is provided as a reference temperature sensor in the same container at a position where it can block the heat from the heater 1. A portable moisture detector characterized in that it combines a sensor part in which lead wires for a heater 1 and a temperature sensor 7 are drawn out in the handle part, and a detection control circuit for operating the sensor part.