JP6114960B2 - Temperature measurement method and apparatus using temperature-sensitive liquid crystal - Google Patents

Description

  The present invention relates to a non-contact temperature measurement method.

  A non-contact and simple temperature (distribution) measuring method is required in the field of temperature control and management. Products that meet these needs include infrared cameras and radiation thermometers, which have already been widely used at manufacturing sites. However, although an infrared camera is expensive, there is a measurement error of about several degrees Celsius and it cannot be said that the accuracy is very high. Further, the radiation thermometer also has a problem that the measurement accuracy is low due to the difference in emissivity such as the surface shape and color of the measurement object. If these problems are solved, it will be possible to perform more accurate and rational temperature control, and non-contact temperature measurement will be used in fields that have not been used so far. .

  Therefore, attention is paid to a technique using a temperature-sensitive liquid crystal, which is a temperature measuring method with a high accuracy, although there is a problem that the temperature measurement width is narrowed. The temperature-sensitive liquid crystal has a characteristic that the scattered light changes according to the temperature. In this method, the brightness of the three primary colors of light is measured by a CCD camera, and the temperature is measured using a correlation equation between the brightness and temperature. The method differs depending on how the three primary colors of light are used. The RGB method (Patent Document 1) that tests the temperature using a polynomial with the luminance of the three primary colors of light as an argument, and the luminance of the three primary colors of light in the HSI color space An HSI spline test method (Non-Patent Document 1) has been reported so far in which temperature is verified using the relationship between the Hue value and temperature.

However, these measurement methods require a light source that includes all three primary colors of light and a CCD camera that can acquire the luminance of the three primary colors of light. Since the light source is fixed to the three primary colors of light, fluctuations in the wavelength shorter than the wavelength that can be captured as blue are not captured, and temperature measurement on the high temperature side of the temperature-sensitive liquid crystal color range (temperature range in which the color changes) Has a problem that the range that can be measured is narrowed. Actually, the temperature difference that is the coloration range of the temperature-sensitive liquid crystal usually has a temperature range of 10 ° C., although it depends on the purification method of the temperature-sensitive liquid crystal. However, the above-described measurement method has a problem that even a temperature-sensitive liquid crystal having a temperature range of about 10 ° C. can measure only a range of about 7 ° C. In addition, the color CCD camera is a factor that makes it difficult to reduce the size and price of the measurement system.
An object of the present invention is to look at wavelength ranges other than the three primary colors of light, find wavelengths having a high relationship with temperature, and more easily find a temperature measurement principle with a wider measurement range. Therefore, the intensity of each wavelength of the scattered light of the temperature-sensitive liquid crystal was measured with a spectrometer, and the relationship between the wavelength intensity and temperature was clarified.

JP2003-337070

Study on temperature measurement with thermosensitive liquid crystal (1st report, Spectral and color characteristics), Transactions of the Japan Society of Mechanical Engineers, B, Vol.63, No.611, pp.2473-2479,1997.

  An object of the present invention is to look at wavelength regions other than the three primary colors of light, find a wavelength having a high relationship with temperature, and more easily find a temperature measurement principle with a wider measurement range. Therefore, the intensity of each wavelength of the scattered light of the temperature-sensitive liquid crystal was measured with a spectrometer, and the relationship between the wavelength intensity and temperature was clarified.

  To achieve the above object, the present invention can be achieved by the following configurations of the present invention.

  The measurement method of the present invention is a temperature measurement method using a temperature-sensitive liquid crystal, and uses a region in which the relationship between luminance and temperature is monotonously increasing in a wavelength region (less than 490 nm) corresponding to a blue portion of visible light. A temperature measurement method characterized by measuring temperature.

  As an apparatus for carrying out the present invention, a temperature-sensitive liquid crystal fixed in powder, liquid, or sheet form, a light source capable of emitting one or more wavelengths among short wavelengths, and reflected luminance are measured. This is a temperature measuring device composed of a photodiode that can be used.

  Next, an embodiment of the present invention will be described. The present invention includes a temperature-sensitive liquid crystal fixed in powder, liquid, or sheet form, a light source capable of emitting one or more wavelengths among short wavelengths, and a photodiode capable of measuring reflected luminance. That's fine. An outline of the experimental apparatus is shown in FIG.

The outline of the device of the present invention is shown. A photograph of the experimental apparatus is shown. The relationship of the signal intensity corresponding to the brightness | luminance of all the wavelength ranges obtained from the spectrometer in typical temperature is shown. The measurement result of the signal intensity ratio normalized using the white board is shown. The measurement results over a slightly wider temperature range (25 to 40 ° C) than the color range (28.8 to 35.5 ° C) of the temperature-sensitive liquid crystal are shown. The relationship between the signal intensity ratio at 470, 480 and 490 nm and the temperature is shown.

  A photograph of the experimental apparatus is shown in FIG. Preliminary experiments revealed that the temperature of the temperature-sensitive liquid crystal would rise if irradiation with a halogen light source was continued. Therefore, the sensor unit was moved at a constant speed using an electric moving stage. As a result, the halogen light is not irradiated to the same portion over a long period of time, so that the influence of the halogen light can be minimized. In this experiment, measurement is performed while being moved by an electric moving stage. Therefore, the smaller the rate of change in temperature distribution, the more accurate measurement is possible. The vertical direction is the direction of sensor movement. Therefore, a heat transfer plate with a length of 230 mm and a width of 370 mm was manufactured, and constant temperature water was circulated at both ends of the heat transfer plate to form a temperature distribution. The sensor was placed perpendicular to the temperature-sensitive liquid crystal, and halogen light for obtaining scattered light was applied from an angle of 45 °. Since the spectroscope and the electric moving stage could not be synchronized, it was necessary to manually synchronize the experiment. In order to accomplish this, a start line and a start check line as shown in FIG. 1 were installed on the heat transfer surface with a kite string at intervals of 2 cm. Since the shortest measurement interval of the spectrometer is 1 second and the minimum moving speed of the electric moving stage is 1 cm / s, it is necessary to set the interval between the start line and the start check line in multiples of 1 cm. In the present invention, the distance is set to 2 cm for ease of installation. As the temperature of the temperature-sensitive liquid crystal, a T-type thermocouple (14 points in total) installed at equal intervals of 2 cm and a temperature of 23 points obtained by interpolation between them were used.

Table 1 shows the set temperature of the constant temperature water in this experiment and the room temperature during the experiment. In this experiment, scattered light outside the color range of the temperature-sensitive liquid crystal is also measured.However, if the temperature is set so that a wide temperature range can be measured in one experiment, the temperature range of the data becomes too large. The accuracy will be greatly affected. Therefore, three types of measurements were performed by changing the temperature range. Note that the room temperature is adjusted so that the room temperature is in the vicinity of the middle of the constant temperature water flowing through both ends of the heat transfer plate so as not to adversely affect the formation of a uniform temperature distribution.
The temperature-sensitive liquid crystal used in this experiment is in the form of a sheet, and the color range is 28.8-35.5 ° C. Table 2 summarizes the sheet structure when the surface that is exposed to halogen light is the front surface and the surface that contacts the heat transfer plate is the back surface. The sheet 1 is a commercially available temperature-sensitive liquid crystal, and five types with different sheet structures were prepared for the purpose of reducing the influence of reflection of incident halogen light. Details of each material used for the sheet are shown in Table 3.

Experimental Method First, the room temperature is set to a temperature near the middle between the high temperature side and the low temperature side of the thermostatic water bath. Further, the high temperature side of the heat transfer plate where constant temperature water is flowing is affected by cooling at room temperature, and the low temperature side is affected by heating. Therefore, the set temperature of the thermostatic water tank is adjusted to be higher and lower than the actual temperature to be measured so that an arbitrary temperature distribution is formed.

The temperature setting is completed when it is confirmed that the temperature is measured by a thermocouple set on the heat transfer plate, does not vary for a certain period of time, and the temperature distribution is substantially constant with respect to the position. While the temperature is set, the electric moving stage and the spectroscope are set. Here, the electric moving stage was moved at a constant speed of 1 cm / s, and the spectroscope was set to measure a total of 23 times per second. After the temperature setting is completed, the constant speed movement of the electric moving stage is started from before the start line, and at the same time as the sensor passes the start line, the measurement with the spectroscope is started manually to measure the scattered light. If measured correctly, the second data measured by the spectrometer will measure the value of the kite string, and the remaining data will all be measured at the location where the thermocouple is installed. In addition, since the color of the kite string is white, the value measured by the spectroscope can be easily confirmed because a large value is measured in a wide wavelength range.

Experimental Results and Discussion As a result of a preliminary experiment using a halogen light source, the temperature-sensitive liquid crystal other than the sheet 4 was not able to measure greatly the influence of reflection by the surface material. In addition, when measuring with a measuring instrument that can measure the reflectance of any wavelength using a photodiode and LED light source with sufficient amplification factor, measurement of the intensity of the wavelength according to the wavelength of the LED light source irradiated on all sheets Is confirmed to be possible. Therefore, it is considered that the thermosensitive liquid crystal whose surface is generally covered with PET can be applied by improving the measuring instrument side.
The purpose of the present invention is to examine the relationship with temperature for various wavelength ranges using a spectroscope, so the following results and conclusions show the results of an experiment conducted with halogen light on the sheet 4 and evaluation.

Characteristics of Light Source FIG. 3 shows the relationship between signal intensities corresponding to the luminance in all wavelength regions obtained from a spectroscope at typical temperatures. The horizontal axis is the wavelength and the vertical axis is the signal intensity. It can be seen that this signal intensity is undulating. This is because the output of the spectrometer used is not a type that outputs calibrated data, but a mechanism that calibrates the obtained data later. In order to perform calibration, scattered light data of a calibration plate called a white plate is used. This calibration can be performed only by the spectroscope manufacturer, and has a drawback that it cannot be easily performed each time. Therefore, in the present invention, the signal intensity measured using the scattered light of the white plate as a denominator is normalized and evaluated as a signal intensity ratio.

FIG. 4 shows the measurement result of the signal intensity ratio normalized using the white plate. The horizontal axis is the wavelength, and the vertical axis is the signal intensity ratio. When normalization is performed in this manner, the undulation as seen in FIG. 3 is not observed.

FIG. 5 shows the measurement results over a temperature range (25 to 40 ° C.) that is slightly wider than the color range (28.8 to 35.5 ° C.) of the temperature-sensitive liquid crystal. The horizontal axis is the wavelength, and the vertical axis is the signal intensity ratio. Although the difference cannot be confirmed with the naked eye in the temperature range outside the coloration range, it can be seen that the signal intensity ratio is different even outside the coloration range. Here, when attention is paid to less than 500 nm, it seems that the signal intensity ratio tends to increase as the temperature rises. Therefore, the relationship between the signal intensity ratio of 470, 480 and 490 nm and the temperature is shown in FIG. In particular, it can be seen that at 480 nm, this relationship is maintained in a temperature range exceeding the coloration range. In other words, by using a signal intensity ratio of a single wavelength (480 nm), the temperature in the 12.4 ° C range (25-37.4 ° C) can be verified, and the measurement device can be simplified because there is only one single wavelength intensity. It can be said that was shown.

Claims (2)

In the temperature measurement method using a temperature-sensitive liquid crystal, the temperature- sensitive liquid crystal is measured using a region in which the relationship between luminance and temperature is monotonically increasing in a wavelength region (less than 490 nm) corresponding to a blue portion of visible light. A temperature measurement method for obtaining a temperature value of the temperature-sensitive liquid crystal from the measured luminance Temperature sensitive liquid crystal fixed in powder, liquid or sheet form;
A light source capable of emitting one or more wavelengths of short wavelengths;
A temperature measuring device comprising a photodiode capable of measuring the reflected luminance and obtaining the temperature of the temperature-sensitive liquid crystal from the measured luminance

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