Principle and production of measuring instruments

In physical experiments and production practice, high-precision measurements are often required. The influence of ambient temperature on measurement is an important factor. Therefore, we must measure the ambient temperature accurately. The measuring instrument should also have the following requirements, that is, low manufacturing cost and high measurement accuracy. Humidity sensor probe, stainless steel electric heating tube, PT100 sensor, fluid solenoid valve, cast aluminum heater, heating coil

Good linearity and wide application range. Easy to install and debug. There are many sensors on the market that can be used to measure temperature. Commonly used ones include quartz thermometers, fiber optic sensor thermometers, thermistor thermometers, etc. Among the above devices, quartz thermometers have the highest sensitivity, which can currently reach the order of ℃. However, the prices of these sensors are generally expensive. Linearity is difficult to meet the requirements of precision measurement.

We know that the characteristics of infrared light are: good monochromaticity, anti-interference, and more suitable for high-precision measurement. The instrument we want to design has a simple structure, is easy to make, and is easy to install. It can perform high-precision temperature measurement. The temperature measurement can be directly output to a microcomputer or PC for later data processing, which is very convenient and easy.

2. Principle and purpose of the instrument

We use micro-glass ceramics to make a cylinder. This micro-glass ceramic material has good vacuum properties, high and low temperature resistance, insulation and acid and alkali corrosion resistance. Its basic performance indicators are as follows: operating temperature -273℃～1000℃, volume resistivity 1.08x1014Ω·cm, thermal expansion coefficient αl=8.6x10-6/℃, micro-glass ceramics have very good thermal shock resistance, and will not break when rapidly cooled from 800℃ to 0℃, and the strength will not change when rapidly cooled from 200℃ to 0℃. A thin organic glass cylinder with a length of L=10cm is fixed at one end of the cylinder, and an infrared displacement sensor is fixed at the other end of the cylinder, and the free end of the organic glass rod covers half of the receiving surface of the infrared receiving tube, so that it works in the area with the best linearity. Since the thermal expansion coefficient of organic glass is α2=1.7x10-4/℃, the difference between the two is 2 orders of magnitude, so when the temperature changes, we can assume that the relative displacement of organic glass on the ceramic card material can be ignored. Therefore, the relative position change between the free end of organic glass and the infrared displacement sensor will change the effective receiving area of ​​the infrared receiving tube. As a result, the output voltage of the displacement sensor will also change. The measurement sensitivity of this new temperature sensor is:

ΔT=ΔL/L(α1-α2)

Among them, △L is the sensitivity of the infrared displacement sensor to the length measurement of organic glass.

The infrared displacement sensor is mainly composed of an infrared light emitting diode transmitting and receiving device, a data amplification and denoising part, and a data acquisition and processing system.

We can see that it uses the photoelectric conversion law of infrared photodiodes to determine the obstruction through the relationship between the light flux blocked and the output current. It can convert tiny temperatures into voltage changes. It is amplified by using an amplifier circuit. Combined with a data acquisition card, a functional relationship between the voltage signal and the temperature is established. Finally, it is calibrated with a high-precision micrometer, and finally we can get a displacement measuring instrument with high measurement accuracy (3×10-7m).

Since the current of photoelectric conversion is small and the power of infrared light-emitting diode is also low, we can assume that the infrared displacement sensor will not affect the measured temperature environment.

3. Instrument production and experimental results

We put the designed temperature sensor and a quartz thermometer with a sensitivity of 0.001℃ into a copper box, and put them as close as possible to reduce the difference in ambient temperature between them. At the same time, a 1W bulb wrapped in a black box is placed to heat the box. The black box is used to reduce the impact of the background light in the box on the infrared displacement sensor. In the experiment, our data acquisition is based on the PCL-71IB data acquisition card. PCL-711B is a high-performance, high-speed, and multi-functional data conversion card, which is suitable for the current IBMPC or other compatible computers. Its high performance, rich software support and multiple functions make PCL-71IB an ideal choice for industrial applications and experimental equipment. We use its A/D conversion function and combine it with serial communication to input data into the PC for post-processing. 0