CN102494807B - Multi-point temperature calibration device for accurately controlling temperature fluctuation of thermostatic water bath box and operation method thereof - Google Patents

Abstract

The invention discloses a multi-point temperature calibration device for accurately controlling temperature fluctuation of a thermostatic water bath box. The multi-point temperature calibration device comprises a thermostatic water bath box. An insulation can body and an insulation cover that is matched with the insulation can body are arranged inside the thermostatic water bath box; a temperature balance outer tube is arranged inside the insulation can body; a temperature balance inner tube is arranged inside the temperature balance outer tube; a platinum resistor and a T type thermocouple are arranged inside the temperature balance inner tube; and a support, which is arranged at a tube entrance of the temperature balance inner tube, is used for fixing the platinum resistor and the T type thermocouple in the temperature balance inner tube without the bottom and the sidewalls of the temperature balance inner tube contacted. Besides, the platinum resistor and the T type thermocouple are connected with a data acquisition instrument that is connected with a computer. According to the invention, beneficial effects are as follows: calibration can be carried out rapidly and conveniently; precision is high; and the apparatus and the method are suitable for a plurality of kinds of thermocouples including a K type thermocouple.

Description

Multi-point temperature calibration device and method for accurately controlling temperature fluctuation of constant temperature water bath box

technical field

The invention relates to a calibration device, in particular to a multi-point temperature calibration device and method for precisely controlling the temperature fluctuation of a constant temperature water bath box.

Background technique

The T-type thermocouple is simple in structure, easy to use, and has the advantages of small time constant and no current self-heating problem, and is widely used in temperature measurement.

The main function of the constant temperature water bath is to provide a constant temperature environment for scientific experiments such as calibration. In the experiment, sometimes it is necessary to use multiple T-type thermocouples, and the temperature measured by each T-type thermocouple is biased. In order to reduce this deviation, the T-type thermocouple needs to be calibrated. Within the temperature range required by the experiment (-20°C to 50°C), use a constant temperature water bath to calibrate the T-type thermocouple for each degree. The existing products have the following defects: first, the water bath fluctuates greatly due to the influence of the machine operation during the test, and the convective heat transfer produces a temperature difference, causing temperature fluctuations and unstable temperature calibration; second, several points of temperature are required during the experiment. The stable value of the constant temperature water bath box cannot continue to stabilize each temperature, the test environment cannot reach the expected goal, and there is a problem of low calibration accuracy.

To sum up, in view of the defects of the prior art, a multi-point temperature calibration device that accurately controls the temperature fluctuation of the constant temperature water bath is particularly needed to solve the above-mentioned problems.

Contents of the invention

The purpose of the present invention is to provide a multi-point temperature calibration device that can accurately control the temperature fluctuation of a constant temperature water bath, which can accurately calibrate T-type thermocouples in the special case where the temperature is difficult to stabilize in the test, and also provides the multi-point temperature calibration device method of operation.

The present invention is achieved through the following technical solutions:

A multi-point temperature calibration device for precisely controlling the temperature fluctuation of a constant temperature water bath box, including a constant temperature water bath box, a heat preservation box is arranged inside the constant temperature water bath box, and a heat preservation cover matched with the heat preservation box body is arranged in the heat preservation box. The temperature balance inner tube is placed in the temperature balance outer tube, the water level in the thermal insulation box is higher than the water level in the temperature balance outer tube, the water level in the temperature balance outer tube is higher than the water level in the temperature balance inner tube, and the temperature balance An anti-interaction device is arranged between the outer tube and the temperature-balanced inner tube, and the anti-interaction device fixes the temperature-balanced inner tube at the center of the temperature-balanced outer tube without touching the bottom and side walls of the temperature-balanced outer tube. Platinum resistors and T-type thermocouples are installed in the temperature-balanced inner tube, and a bracket is set at the nozzle of the temperature-balanced inner tube. The bracket fixes the platinum resistance and T-type thermocouples in the temperature-balanced inner tube without touching the temperature-balanced inner tube. The bottom and side walls of the inner tube, the platinum resistance and the T-type thermocouple are connected to a data acquisition instrument, and the data acquisition instrument is connected to a computer.

Preferably, the anti-interaction device between the temperature balance outer tube and the temperature balance inner tube adopts a support device made of foam plastic with an opening in the center.

Preferably, the bracket at the mouth of the temperature-balanced inner tube is an upper cover made of foam plastic with a plurality of holes.

Preferably, the insulation cover is made of polyurethane foam or foam plastic.

Preferably, the insulation cover is provided with an opening for communication between the platinum resistor, the T-type thermocouple and the data acquisition instrument.

Preferably, the temperature balance inner tube is made of glass or stainless steel.

Preferably, the T-type thermocouple can be replaced by a K-type thermocouple.

Preferably, the platinum resistor is a calibrated platinum resistor.

Preferably, the data acquisition instrument is a Fluke data acquisition instrument.

The operation method steps of the multi-point temperature calibration device for accurately controlling the temperature fluctuation of the constant temperature water bath are as follows:

(1) Pour a certain amount of water into the insulation box of the constant temperature water bath, put the temperature balance outer tube into it, and put the temperature balance inner tube into the temperature balance outer tube;

(2) Use the anti-interaction device to fix the temperature balance inner tube in the center of the temperature balance outer tube, and not touch the cup bottom and cup wall of the temperature balance outer tube, to ensure that the liquid level of the insulated box is higher than the liquid in the temperature balance outer tube The liquid level in the temperature-balanced outer tube is higher than the liquid level in the temperature-balanced inner tube;

(3) Fix several T-type thermocouples and calibrated platinum resistors in the center of the temperature balance inner tube with a bracket, and do not touch the cup wall and cup bottom of the temperature balance inner tube, and do not touch each other at the same time;

(4) Connect the other end of the T-type thermocouple and platinum resistance to the data acquisition instrument, cover the insulation cover, and then connect the data acquisition instrument to the computer;

(5) Set the mode of the data acquisition instrument to read a temperature value every 30s, so that the temperature change can be observed in real time on the computer, and when the required temperature value is adjusted, the value after the temperature is stabilized can be collected. Compare and correct each T-type thermocouple with the temperature value of the platinum resistance at the same temperature;

(6) According to the method of step (5), calibrate the temperature value of each degree within the required temperature range in turn.

Beneficial effects: the present invention can accurately control the multi-point temperature calibration of the temperature fluctuation of the constant temperature water bath, has a simple structure, is easy to manufacture and assemble, and is suitable for various salt water and transformer oil, and the glass container is suitable for beakers, glass test tubes, U Simple and commonly used experimental instruments such as tubes and stainless steel products, and can be used for calibration tests in special cases where the temperature range of the test is large (-20 ° C ~ 50 ° C); it is especially suitable for use in environmental tests that require high calibration accuracy . It has fast, convenient and high-precision calibration, and is suitable for various types of thermocouples including K-type thermocouples.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is a schematic diagram of the internal structure of the calibration device of the present invention.

Fig. 2 is a schematic diagram of the appearance structure of the calibration device of the present invention.

Fig. 3 is a schematic structural view of the bracket at the nozzle of the temperature-balanced inner tube in the present invention.

Figure 4 is a temperature fluctuation curve after the calibration process of directly contacting the T-type thermocouple with the fluid is stable.

Fig. 5 is a curve diagram of temperature fluctuation after the calibration process of adding a glass container is stable.

Fig. 6 is a curve diagram of temperature fluctuation after the calibration process with two glass containers is stabilized.

In the figure: 1. Constant temperature water bath box; 11. Insulation box; 2. Platinum resistance; 3. T-type thermocouple; 4. Temperature balance outer tube; 5. Temperature balance inner tube; 6. Data acquisition instrument; 7. Computer ; 8. Bracket; 9. Insulation cover; 10. Anti-interaction device.

Detailed ways

The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings: this embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following the described embodiment.

As shown in Fig. 1, Fig. 2 and Fig. 3, a constant temperature water bath box 1 is included in the figure, and the thermostatic water bath box 1 is provided with an insulated box body 11, an insulating cover 9 matched with the insulated box body 11, and the insulating cover 9 adopts polyurethane Made of foam or foamed plastic, openings are provided on the insulation cover 9 for the communication circuits of the platinum resistor 2, the T-type thermocouple 3 and the data acquisition instrument 6 to pass through.

The temperature balance outer pipe 4 is arranged in the heat preservation box 11, the temperature balance inner pipe 5 is placed in the temperature balance outer pipe 4, the water level in the heat preservation box 11 is higher than the water level in the temperature balance outer pipe 4, and the temperature balance outer pipe 4 The water level is higher than the water level in the temperature balance inner pipe 5. The temperature balance inner tube 5 is made of glass or stainless steel to prevent heat from dissipating.

An anti-interaction device 10 is arranged between the temperature balance outer tube 4 and the temperature balance inner tube 5. The anti-interaction device 10 is made of foam plastic. The center of the anti-interaction device 10 is provided with an opening embedded in the temperature balance outer tube 4. Used to support the temperature-balanced inner tube 5 , the anti-interaction device 10 fixes the temperature-balanced inner tube 5 in the center of the temperature-balanced outer tube 4 without touching the bottom and side walls of the temperature-balanced outer tube 4 .

A platinum resistor 2 and several T-type thermocouples 3 are arranged in the temperature balance inner tube 5, and a bracket 8 is set at the nozzle of the temperature balance inner tube 5, and the bracket 8 is an upper tube made of foam plastics with a plurality of holes. Cover, platinum resistance 2 and T-type thermocouple 3 pass through the holes on the bracket 8 respectively, and the bracket 8 fixes one end of the platinum resistance 2 and T-type thermocouple 3 in the temperature balance inner tube 5 without touching the temperature balance inner tube The bottom and side walls of 5, the other end of the platinum resistor 2 and the T-type thermocouple 3 are connected to the input end of the data acquisition instrument 6, and the output end of the data acquisition instrument 6 is connected to the computer 7. Data acquisition instrument 6 adopts Fluke data acquisition instrument.

The operation method steps of the calibration device of the present invention:

(1) Pour a certain amount of water into the insulation box of the constant temperature water bath, put the temperature balance outer tube into it, and put the temperature balance inner tube into the temperature balance outer tube;

(2) Use the anti-interaction device to fix the temperature balance inner tube in the center of the temperature balance outer tube, and not touch the cup bottom and cup wall of the temperature balance outer tube, to ensure that the liquid level of the insulated box is higher than the liquid in the temperature balance outer tube The liquid level in the temperature-balanced outer tube is higher than the liquid level in the temperature-balanced inner tube;

(3) Fix several T-type thermocouples and calibrated platinum resistors in the center of the temperature balance inner tube with a bracket, and do not touch the cup wall and cup bottom of the temperature balance inner tube, and do not touch each other at the same time;

(4) Connect the other end of the T-type thermocouple and platinum resistance to the data acquisition instrument, cover the insulation cover, and then connect the data acquisition instrument to the computer;

(5) Set the mode of the data acquisition instrument to read a temperature value every 30s, so that the temperature change can be observed in real time on the computer, and when the required temperature value is adjusted, the value after the temperature is stabilized can be collected. Compare and correct each T-type thermocouple with the temperature value of the platinum resistance at the same temperature;

(6) According to the method of step (5), calibrate the temperature value of each degree within the required temperature range in turn.

Explanation of the experimental principle: Due to the viscosity of the fluid and the influence of the frictional resistance of the wall, a boundary layer with a large velocity gradient will be formed close to the wall. According to Newton's cooling formula:

可以看出换热量是温差与热阻的比值，因此可以发现要控制水浴温Φ＝hA(t_w-t_∞)度波动，只需增h＝Φ/[A(t_w-t_∞)]大热阻即可。It can be known that the surface heat transfer coefficient is the key to controlling the heat transfer of the fluid, that is, the larger the heat transfer coefficient is, the more intense the heat transfer process is, and vice versa. Therefore, reducing the heat transfer coefficient is the core issue of controlling the temperature fluctuation in the water bath. Transformation formula

It can be seen that the heat transfer is the ratio of the temperature difference to the thermal resistance, so it can be found that to control the temperature fluctuation of the water bath Φ=hA(t _w -t _∞ ), it is only necessary to increase h=Φ/[A(t _w -t _∞ ) ] Large thermal resistance is sufficient.

When the constant temperature water bath box is working, the temperature in the box fluctuates periodically due to heating or cooling, and is transmitted to the surface of the measured object through the fluid medium. At this time, the interior of the insulated box is equivalent to a homogeneous semi-infinite object, and the temperature on the surface of the object will also change periodically, that is, θ=A _w cosωτ(θ is the instantaneous excess temperature on the surface of the object, indicating that the fluid The difference between the instantaneous temperature and the average temperature, Aw is the fluctuation amplitude of the surface temperature, ω is the fluctuation frequency, and τ is the time) and the fluctuation characteristics are reflected by the change of the simple harmonic wave. Affected by the initial temperature distribution, the periodic change of the temperature of the object is in The initial stage is irregular, and then enters the steady state stage. At this time, it can be obtained by the method of separation of variables:

$\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; COS</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;\&tau;</span>}<span\; class="notranslate">\; -</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; )</span>$

(α is the thermal diffusivity of the material, and x is the position of the temperature amplitude of the object).

The amplitude of fluctuation at x is

It shows that the fluctuation amplitude inside the object decreases with the depth, which is an important feature of periodic heat conduction, that is, the amplitude of the temperature wave gradually decays with the increase of the distance from the inner surface.

When the present invention is working, due to the large temperature balance inner tube inside the heat preservation box, the thermal resistance is increased and the heat exchange is reduced, thereby obtaining a good constant temperature environment. The glass thermal resistance between the heat preservation box and the temperature balance outer pipe, the temperature balance outer pipe and the temperature balance inner pipe can prevent temperature fluctuations caused by convective heat transfer during the test. The principle is: According to Pollhausen’s analytical solution to the natural convection boundary layer equation and Schmidt Beckmann’s measurement results, it can be known that under convective heat transfer, the uneven temperature field only occurs between the thin layers near the heat transfer wall. Inside, the temperature balance outer tube is placed in the insulation box, and the temperature balance inner tube is placed inside the temperature balance outer tube. Due to the existence of the glass container, the distance between the thermocouple and the wall during the calibration process is increased, that is, the distance between the thermocouple and the surface is increased. , attenuates the amplitude of the temperature wave, which can effectively prevent the temperature fluctuation caused by convective heat transfer.

The external dimension of the constant temperature water bath box of the present invention is L×W×H (mm): 250×200×200, the diameter of the working tank: 180×140, the capacity: 6L, the temperature adjustment range: -30～100°C, the temperature control accuracy: ± 0.02°C.

Standard insulated glass container size D×H(mm): large size 100×120, small size 75×100, optional materials: beaker, glass test tube, U-shaped tube, etc. instrument.

Polyurethane foam insulation cover: foam glass or foam plastic coated with nano-airgel. Dimensions L×W×H (mm): 250×200×100.

Example:

Use water as the experimental medium, adjust the temperature of the constant temperature water bath to 20°C, and calibrate according to the above test method. If the T-type thermocouple is directly in contact with the fluid, the distance between the amplitude of the temperature wave and the surface of the T-type thermocouple is zero. Due to the existence of the glass container, the amplitude of the temperature wave is attenuated accordingly, so as to achieve the purpose of reducing the temperature fluctuation, reduce the calibration error, and make the T-type thermocouple calibration more accurate.

As shown in Figure 4, Figure 5 and Figure 6, Figure 4 is the temperature fluctuation curve after the calibration process of directly contacting the T-type thermocouple with the fluid is stable; Figure 5 is the temperature fluctuation curve after the calibration process of adding a glass container is stable ; Fig. 6 is a curve diagram of temperature fluctuation after the calibration process of two glass containers is stabilized. The results show that the calibrated temperature wave amplitude of directly contacting the T-type thermocouple with the fluid is 0.075°C, and the calibrated temperature wave amplitudes of adding one and two glass containers are 0.03 and 0.02 respectively, which shows that increasing the wall resistance and T-type thermocouple The surface distance can achieve the purpose of accurate calibration.

The basic principles and main features of the present invention and the advantages of the present invention have been shown and described above. Those skilled in the industry should understand that the present invention is not limited by the above-mentioned embodiments. What are described in the above-mentioned embodiments and the description only illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have Variations and improvements are possible, which fall within the scope of the claimed invention. The protection scope of the present invention is defined by the appended claims and their equivalents.

Claims (8)

1. accurately control the multi-point temp caliberating device of constant water bath box temperature fluctuation, comprise constant water bath box, one thermal-insulating body is set in this constant water bath box, the insulation cover that matches with thermal-insulating body and arrange, set temperature balance outer tube in described thermal-insulating body, laying temperature balance inner tube in this equalized temperature outer tube, it is characterized in that, water level in described thermal-insulating body is higher than the water level in the equalized temperature outer tube, water level in described equalized temperature outer tube is higher than the water level in the equalized temperature inner tube, the one anti-device that touches mutually is set between described equalized temperature outer tube and equalized temperature inner tube, should anti-ly touch mutually device and the equalized temperature inner tube was fixed on the central authorities of equalized temperature outer tube, and do not touch bottom and the sidewall of equalized temperature outer tube, in described equalized temperature inner tube, platinum resistance is set, T-shaped thermopair, the mouth of pipe place of described equalized temperature inner tube arranges a support, this support is with platinum resistance, T-shaped thermopair is fixed in the equalized temperature inner tube, and do not touch bottom and the sidewall of equalized temperature inner tube, described platinum resistance, T-shaped thermopair connects a data collecting instrument, this data collecting instrument connects computing machine.

2. the multi-point temp caliberating device of accurate control constant water bath box according to claim 1 temperature fluctuation, it is characterized in that, the anti-device that touches mutually between described equalized temperature outer tube and equalized temperature inner tube adopts the central authorities of being made by polyfoam to be provided with the bracing or strutting arrangement of opening.

3. the multi-point temp caliberating device of accurate control constant water bath box according to claim 1 temperature fluctuation, is characterized in that, the support at described equalized temperature inner tube mouth of pipe place is a upper cover that has a plurality of holes of being made by polyfoam.

4. the multi-point temp caliberating device of accurate control constant water bath box according to claim 1 temperature fluctuation, is characterized in that, described insulation cover adopts polyfoam to make.

5. the multi-point temp caliberating device of accurate control constant water bath box according to claim 1 temperature fluctuation, is characterized in that, the opening that communicates for described platinum resistance, T-shaped thermopair and data collecting instrument is set on described insulation cover.

6. the multi-point temp caliberating device of accurate control constant water bath box according to claim 1 temperature fluctuation, is characterized in that, described equalized temperature inner tube adopts glass material or stainless steel.

7. the multi-point temp caliberating device of accurate control constant water bath box according to claim 1 temperature fluctuation, is characterized in that, described T-shaped thermopair is replaced by K type thermopair.

8. the multi-point temp caliberating device of accurate control constant water bath box according to claim 1 temperature fluctuation, is characterized in that, described platinum resistance adopts the platinum resistance of demarcating.

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