Dew point measuring method capable of accurately controlling temperature

Abstract

The invention belongs to the technical field of dew point measurement, and relates to an accurate temperature control dew point measurement method, which comprises the following steps of: fitting a hot end of a thermoelectric refrigerating unit with a cold mirror surface, fitting a cold end of the thermoelectric refrigerating unit with a cold head of a compressor, and controlling the temperature of the cold head of the compressor to be lower than an estimated dew point temperature; the thermoelectric refrigerating unit is controlled to heat, so that the cold mirror surface temperature is higher than the estimated dew point temperature; feeding a sample gas into the cavity to keep stable ventilation; the heating power of the thermoelectric refrigerating unit is gradually reduced, so that the temperature of the cold mirror surface is gradually reduced until the intensity of the reflected light signal monitored by the light receiver is suddenly reduced, and at the moment, the cold mirror surface is just condensed; the heating power of the thermoelectric refrigerating unit is controlled, so that the temperature of the cold mirror surface is stably kept at the condensation temperature for a period of time; and the dew-point temperature is obtained by reading the reading of the temperature sensor. The thermoelectric refrigerating unit is reversely arranged, higher measurement precision is obtained through reverse heating of the thermoelectric refrigerating unit, meanwhile, the temperature of the cavity where the cold mirror surface is located is constant, and the measurement precision is improved.

Description

A precise temperature-controlled dew point measurement method Technical Field

[0001] This invention belongs to the field of dew point measurement technology, specifically relating to a precise temperature-controlled dew point measurement method. Background Technology

[0002] A cold mirror dew point meter is a measuring device that uses the cold mirror dew point method to measure the humidity of a gas. Its main components include a dew point sensor and a thermoelectric cooler.

[0003] A cold mirror dew point meter uses a thermoelectric cooler or other cooling device to cool the mirror surface of the dew point sensor, while the gas being measured continuously blows across the mirror. When the mirror temperature drops to the dew point temperature, water vapor in the gas begins to condense on the mirror surface, forming tiny dew droplets or frost. To accurately capture the critical condensation state, the instrument is equipped with a photoelectric system consisting of a light source and a photosensitive element to collect the reflected light signal from the mirror. When condensation occurs on the mirror, the intensity of the reflected light is significantly reduced due to the diffuse reflection effect of dew droplets or frost crystals. An automatic control circuit precisely maintains the mirror temperature at a phase equilibrium state where condensation just begins. At this point, a platinum resistance temperature sensor accurately measures the current temperature of the mirror, thus obtaining the dew point temperature of the gas.

[0004] Currently, thermoelectric coolers (also known as semiconductor coolers, TECs) are commonly used to cool mirror surfaces. When an electric current is applied, the thermoelectric cooler absorbs heat from its cold end and releases it to its hot end. Temperature control can be achieved by precisely controlling the input electrical power, which adjusts the heat absorption power at the cold end. However, thermoelectric coolers have limited cooling capacity and cannot reach extremely low temperatures.

[0005] Chinese patent CN201740753U discloses a dual-cooling dew point meter. It employs a compressor cooler for the first stage of cooling, then connects the hot end of a thermoelectric cooler to the cold head of the compressor cooler, and the cold end of the thermoelectric cooler to a mirror surface for the second stage of cooling. Due to the strong cooling capacity of the compressor, temperature control is achieved through superimposed cooling, enabling the measurement of extremely low-temperature dew points.

[0006] While this temperature control method can achieve extremely low cooling temperatures, it suffers from the following problems: Due to the low temperature control precision of compressor cooling, the temperature is difficult to precisely control after being combined with a thermoelectric cooler, making it impossible to accurately maintain the mirror at the dew point temperature. Furthermore, the compressor cooling alters the cold head temperature, causing temperature changes in the measuring chamber. At ultra-low temperatures, the photoelectric signal transmitter and receiver are more sensitive to temperature drift. If a stable temperature environment cannot be maintained, the photoelectric signal will be interfered with, making it impossible to effectively determine the current temperature and achieve precise temperature control of the mirror. Consequently, measurement accuracy cannot be guaranteed, resulting in significant measurement errors and failing to meet the technical specifications of a first-class precision dew point meter. In addition, the low cooling efficiency of the thermoelectric cooler leads to slow temperature control of the mirror, resulting in slow measurement speed. Summary of the Invention

[0007] To address the technical problems of low temperature control accuracy in compressor cooling, low temperature control accuracy during the bonding and superposition process with the hot end of the thermoelectric cooler, significant influence of cavity temperature on photoelectric signals in low-temperature environments causing interference with mirror temperature control and resulting in low measurement accuracy, and slow measurement speed, this invention proposes a precise temperature-controlled dew point measurement method. The technical solution adopted by this invention is as follows: A precise temperature-controlled dew point measurement method, comprising the following steps: Step S01, bonding the hot end of the thermoelectric cooler to the cold mirror surface using a thermally conductive material, bonding the cold end of the thermoelectric cooler to the compressor cold head using a thermally conductive material, reducing the temperature of the compressor cold head to below the estimated dew point temperature, and maintaining a constant temperature. Step S02: Control the thermoelectric cooler to heat at high power, so that the temperature of the cold mirror surface is higher than the estimated dew point temperature; Step S03: Send the sample gas into the cavity through the inlet pipe. After passing through the cold mirror surface, the sample gas leaves the cavity through the outlet, maintaining stable ventilation; Step S04: Gradually reduce the heating power of the thermoelectric cooler, so that the temperature of the cold mirror surface gradually decreases until the intensity of the reflected light signal monitored by the light receiver drops sharply. At this time, the cold mirror surface just condenses; Step S05: Control the heating power of the thermoelectric cooler to keep the temperature of the cold mirror surface stable at the temperature at which condensation just occurs for a period of time; Step S06: Read the reading of the temperature sensor to obtain the dew point temperature.

[0008] Preferably, in step S01, the cooling temperature of the compressor is controlled by controlling the duty cycle, and the compressor cold head is adjusted to a fixed low temperature.

[0009] Preferably, in step S02, the heating power of the thermoelectric cooler is controlled by controlling the magnitude of the current.

[0010] Preferably, in step S05, if the intensity of the light signal received by the light receiver remains low, the heating power of the thermoelectric cooler is increased to raise the temperature of the cold mirror surface; conversely, if the intensity of the light signal received by the light receiver is high, the heating power of the thermoelectric cooler is reduced to lower the temperature of the cold mirror surface; this process is repeated for a period of time until the light signal intensity remains stable at a moderate level.

[0011] The beneficial effects of this invention are as follows: Existing technologies use a two-stage cooling system consisting of a compressor and a thermoelectric cooler. This invention innovatively reverses the configuration of the thermoelectric cooler (the first stage is compressor cooling, the second stage is thermoelectric cooler heating). Specifically, the cold end of the thermoelectric cooler is in contact with the cold head of the compressor, and the hot end of the thermoelectric cooler is in contact with the cold mirror surface. By heating the thermoelectric cooler in reverse, higher measurement accuracy is achieved. Simultaneously, during measurement, the cold head of the compressor is locked at a constant temperature, and only the power of the thermoelectric cooler is adjusted, thus maintaining a constant temperature in the cavity containing the cold mirror surface. The resulting measurement accuracy meets the requirements of a first-class precision dew point meter. Due to the precise temperature regulation advantage of the thermoelectric cooler, combined with the constant low-temperature environment provided by the compressor, accurate measurement of the dew point in the range above -60℃ can be achieved, with a measurement accuracy better than ±0.05℃. Attached Figure Description

[0012] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 is a schematic diagram of the structure of the dew point measurement system according to an embodiment of the invention; Figure 2 is a flowchart of the steps of the dew point measurement method according to an embodiment of the invention; wherein, 1 is a light emitter, 2 is an air inlet pipe, 3 is a cold mirror, 4 is a thermally conductive material, 5 is a light receiver, 6 is an air outlet pipe, 7 is a temperature sensor, 8 is a thermoelectric cooler, 9 is a compressor cold head, 10 is a cavity, and 11 is a compressor. Detailed Implementation

[0013] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0014] As shown in Figure 1, in the dew point measurement system, a light emitter 1, a cold mirror 3, a light receiver 5, a thermoelectric cooler 8, and a compressor cold head 9 are installed in a cavity 10. A temperature sensor 7 is installed on the cold mirror 3. The hot end of the thermoelectric cooler 8 is bonded to one side of the cold mirror 3 using a thermally conductive material 4, and the cold end of the thermoelectric cooler 8 is bonded to the compressor cold head 9 using the same thermally conductive material 4. The compressor 11 passes through the cavity 10 and is connected to the compressor cold head 9. By setting the duty cycle, the cooling temperature of the compressor cold head 9 is controlled at approximately -60°C and kept constant. By controlling the current direction of the thermoelectric cooler 8, the hot end bonded to the cold mirror is in a heated state, while the cold end bonded to the compressor cold head 9 is in a cooled state. An interconnected inlet pipe 2 and outlet pipe 6 pass through the cavity 10. A light emitter 1 and a light receiver 5 are installed on the pipes formed by the inlet pipe 2 and the outlet pipe 6, tilted at a certain angle, facing the other side of the cold mirror 3. At this time, the current of the thermoelectric cooler 8 is adjusted according to the strength of the light signal reflected by the cold mirror 3 received by the light receiver 5, thereby increasing or decreasing the heating amount of the cold mirror 3, so as to achieve precise control of the temperature of the cold mirror 3 and keep the cold mirror 3 in a state of phase equilibrium with water vapor.

[0015] As shown in Figure 2, a method for precise temperature control of dew point measurement includes the following steps: Step S01, reducing the temperature of the compressor cold head 9 to below the estimated dew point temperature and keeping it constant.

[0016] Specifically, the cooling temperature of compressor 11 is controlled by adjusting the duty cycle, thereby adjusting the compressor cold head 9 to a fixed low temperature value, such as -60℃. The "estimated dew point temperature" can be estimated based on the type of sample gas and past experience, or obtained through rapid testing to obtain a rough estimate of the dew point temperature. The estimated dew point temperature can be interpreted as the lower limit of the dew point that the dew point meter wants to measure. The fixed low temperature point determines the lower limit of the dew point measurement of the device. For example, if the compressor cold head 9 is fixed at a low temperature of -60℃, then the measurement lower limit is approximately -55℃ to -58℃. This invention can measure dew points within a range, such as -20℃ to -58℃, without requiring multiple adjustments to the fixed low temperature value.

[0017] Since the compressor cold head 9 is located in the lower part of the cavity 10 and has a large heat capacity, after the temperature of the compressor cold head 9 is fixed, the temperature field in the cavity 10 is in a relatively stable state, which avoids temperature drift of the light transmitter 1 or the light receiver 5 caused by temperature changes in the cavity 10, and ensures the stability and accuracy of the photoelectric signal.

[0018] Step S02: The thermoelectric cooler 8 heats the surface of the cold mirror 3 at high power, making the temperature of the cold mirror surface 3 higher than the estimated dew point temperature.

[0019] Specifically: The thermoelectric cooler 8 is activated, and its heating power is controlled by adjusting the current, keeping the cold mirror surface 3 dry and free of condensation. "Condensation" includes both droplet condensation and ice crystal frosting.

[0020] Step S03: The sample gas is sent into the cavity 10 from the inlet pipe 1. After passing through the cold mirror 3, the sample gas leaves the cavity 10 from the outlet 5; maintain stable ventilation.

[0021] Step S04: Gradually reduce the heating power of the thermoelectric cooler 8 to gradually lower the temperature of the cold mirror 3 until the light receiver 5 detects a sudden decrease in the intensity of the reflected light signal. At this point, the cold mirror 3 just begins to condense.

[0022] After the temperature of the cold mirror 3 drops to the dew point temperature, condensation occurs on the cold mirror 3. Due to the diffuse reflection effect of the condensate droplets or ice crystals, the intensity of the light signal received by the light receiver 5 decreases significantly, at which point condensation occurs.

[0023] Taking advantage of the fact that the heating efficiency of the thermoelectric cooler 8 is much higher than its cooling efficiency, the above method can adjust the temperature more quickly and greatly shorten the time required for dew point measurement.

[0024] Step S05: Control the heating power of the thermoelectric cooler 8 to keep the temperature of the cold mirror 3 stable at the temperature at which condensation just occurs for a period of time.

[0025] Specifically: If the light signal intensity received by the light receiver 5 remains consistently low, it indicates that the cooling may have been excessive, and the temperature of the cold mirror 3 has fallen below the dew point temperature. In this case, the heating power of the thermoelectric cooler 8 should be increased to raise the temperature of the cold mirror 3. Conversely, if the light signal intensity received by the light receiver 5 is high, it indicates that the condensate has evaporated, and the temperature of the cold mirror 3 is above the dew point temperature. In this case, the heating power of the thermoelectric cooler 8 should be reduced to lower the temperature of the cold mirror 3. This process should be repeated for a period of time until the light signal intensity stabilizes at a moderate level. At this point, the cold mirror 3 exhibits a phase equilibrium state where the condensation and evaporation rates are equal, and the temperature of the cold mirror 3 at this point is the accurate dew point temperature.

[0026] Step S06: Read the reading of temperature sensor 7.

[0027] By adjusting the input current of the thermoelectric cooler 8, and leveraging its precise temperature control advantage and higher heating efficiency compared to its cooling efficiency, the heating temperature is superimposed on the temperature of the compressor cold head 9 to achieve precise temperature control above -50℃. The temperature control accuracy of the cold mirror surface 3 is significantly improved, reaching a control accuracy better than ±0.05℃.

[0028] Thermoelectric cooler 8 has a higher heating efficiency than cooling efficiency. Under the same current, it offers a wider temperature regulation range and faster response in heating mode. The specific principle is explained below: When cooling, thermoelectric cooler 8 transfers heat from the cold end to the hot end, achieving a high coefficient of performance (COP). cooling for:

[0029] Among them, Q c P is the heat absorption power at the cold end. in COP represents the electrical power supplied to thermoelectric cooler 8. cooling The coefficient of performance (COP) is typically below 0.8, and can drop below 0.3 under large temperature differences. According to the law of conservation of energy, the COP for heating a thermoelectric cooler in reverse heating mode is... heating for:

[0030] Q h This represents the heat dissipation power at the hot end. Therefore, the coefficient of performance (COP) for heating is... heating The total value is greater than 1, and the heating efficiency of the same thermoelectric cooler 8 is much higher than its cooling efficiency. During the dew point measurement process, the heating is performed by adjusting the electric power through the control circuit. Its heat transfer efficiency and response speed are much higher than those of the traditional cooling mode. Therefore, it can more accurately and quickly follow the light signal to adjust the temperature of the cold mirror 3, with less hysteresis, and the measurement accuracy can be improved to within ±0.05℃.

[0031] The compressor 11 can be a Stirling refrigerator, a conventional compressor, or other refrigeration compressors. Alternatively, it can be replaced by other equipment or methods that can generate constant low-temperature conditions, such as the use of low-boiling-point inert gases like liquid nitrogen or liquid argon to provide an ultra-low temperature environment. The temperature control range of the compressor 11 can be set to any fixed temperature within the range of (-120 to -10)℃, or it can be used in a segmented manner. For example, when the dew point is measured below -20℃, the temperature of the compressor cold head 9 can be controlled at -60℃, and when the dew point is measured above -20℃, the temperature of the compressor cold head 9 can be controlled at -30℃.

[0032] Temperature sensor 7 can be a platinum resistance thermometer.

[0033] In the embodiments of the present invention, all technical features not described in detail are existing technologies or conventional technical means, and will not be repeated here.

[0034] Finally, it should be noted that the above embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit them. The scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any person skilled in the art can modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention.

Claims

1. A method for precisely controlling the temperature of dew point measurement, characterized in that, Includes the following steps: Step S01: Attach the hot end of the thermoelectric cooler to the cold mirror surface using a thermally conductive material, and attach the cold end of the thermoelectric cooler to the compressor cold head using a thermally conductive material. Reduce the temperature of the compressor cold head to below the estimated dew point temperature and maintain it constant. Step S02: Control the thermoelectric cooler to heat at high power, making the temperature of the cold mirror surface higher than the estimated dew point temperature. Step S03: Introduce the sample gas into the cavity through the inlet pipe. After passing through the cold mirror surface, the sample gas exits the cavity through the outlet, maintaining stable ventilation. Step S04: Gradually reduce the heating power of the thermoelectric cooler, causing the temperature of the cold mirror surface to gradually decrease until the intensity of the reflected light signal detected by the light receiver drops sharply, at which point condensation occurs on the cold mirror surface. Step S05: Control the heating power of the thermoelectric cooler to maintain the temperature of the cold mirror surface stably at the temperature at which condensation occurs for a period of time. Step S06: Read the temperature sensor reading to obtain the dew point temperature.

2. The method for precise temperature control and dew point measurement according to claim 1, characterized in that, In step S01, the cooling temperature of the compressor is controlled by controlling the duty cycle, and the compressor cold head is adjusted to a fixed low temperature.

3. The method for precise temperature control and dew point measurement according to claim 1, characterized in that, In step S02, the heating power of the thermoelectric cooler is controlled by controlling the magnitude of the current.

4. The method for precise temperature control and dew point measurement according to claim 1, characterized in that, In step S05, if the intensity of the light signal received by the optical receiver remains low, the heating power of the thermoelectric cooler is increased to raise the temperature of the cold mirror surface; conversely, if the intensity of the light signal received by the optical receiver is high, the heating power of the thermoelectric cooler is reduced to lower the temperature of the cold mirror surface; this process is repeated for a period of time until the light signal intensity remains stable at a moderate level.

Images