Thermal resistance is one of the most commonly used temperature detectors in low and medium temperature regions. Thermal resistance temperature measurement is based on the characteristic that the resistance of metal conductor increases with the increase of temperature. Its main characteristics are high precision and stable performance. Most thermistors are made of pure metal materials. Platinum and copper are the most widely used materials at present. In addition, nickel, manganese and rhodium have been used to make thermistors. Among them, platinum thermal resistance has the highest measurement accuracy. It is not only widely used in industrial temperature measurement, but also made into a standard reference instrument.
As platinum resistance is a kind of widely used thermal resistance temperature sensor, this paper focuses on the introduction. Platinum resistance sensor PTC is essentially a kind of thermistor. The resistivity of metals increases with temperature, so this property is used to measure temperature. Thin film platinum resistor, because of its ultra-thin structure, is equipped with a glass sleeve to protect the resistance. At present, the resistance value of platinum resistance is 100ohm (at 0 ℃), which is the current international platinum resistance. In addition, when this kind of sensor is used to measure the time of the platinum sensor, it is very slow to use this method when the platinum wire is embedded into the ceramic matrix Food technology, especially laboratory R & D.
There are three types of temperature probes made of thermal resistance temperature sensors
1. Penetration / immersion probe: used to measure the temperature of liquid and solid. The front end of the probe is designed as a needle penetration type. When using, if the temperature of the measuring probe is lower than that of the measured object, according to the principle of energy conservation, the heat energy will be transferred from the measured object to the probe; if the temperature of the measuring probe is higher than the measured object, the heat energy will be transmitted from the probe to the object to be measured. This means that the measured object is heated and heated, and the measured temperature is the object temperature after heating. In this measurement situation, the ratio of probe to medium must be considered, because the better the ratio of probe to medium, the more accurate the energy obtained by the object can be measured. Due to the reason of energy transfer, the measurement error will occur. We must pay attention to the temperature of the sensor rather than the temperature of the medium measured by the instrument. This measurement error can be reduced by the following ways: the depth of penetration or immersion is 10 or 15 times the diameter of the probe; when measuring liquid, the error can be effectively reduced by holding the liquid flow as far as possible.
2. The air temperature probe is used to measure the air temperature, such as cold storage, freezer, air conditioning room (temperature regulation), ventilation (ventilation / exhaust), etc. the sensor of air probe is exposed, so the indication value is easily affected by air flow. The best solution is to move the probe along the flow when the air flow is 2-3m / s, so that the temperature can reach balance and stability.
3. A surface probe used to measure the surface temperature of an object. The air temperature probe and the surface probe are used Surface temperature measurement The front end of the probe must be perpendicular to the measured object and fully contact with the measured object. It must be noted that the contact surface between the probe and the measured object must be flat, otherwise the measurement results will be affected.
The temperature probe adopts contact method, which is mainly used in food sampling inspection, temperature monitoring during food transportation, temperature measurement of flue gas center in flue, temperature difference measurement of different points, surface temperature measurement during electronic welding, immersion measurement of chemical solution temperature during chemical reaction process, and mechanical manufacturing industry, For the maintenance of gear surface and temperature measurement.
The thermal resistance temperature sensor has the following structure types:
1) According to the temperature measurement principle of thermal resistance, the change of measured temperature is directly measured by the change of resistance value of thermal resistance. Therefore, the change of lead resistance of lead wire of thermal resistance body will affect the temperature measurement. In order to eliminate the influence of lead resistance, three wire system or four wire system is adopted.
2) Armored thermal resistance armored thermal resistance is a solid body composed of temperature sensing element (resistance body), lead wire, insulating material and stainless steel sleeve. Its outer diameter is generally φ 2 ~ φ 8mm, and the minimum diameter can be up to φ 1mm. Compared with ordinary thermal resistance, it has the following advantages: 1) small volume, no air gap inside, small measurement lag in thermal inertia; 2) good mechanical performance, vibration resistance and impact resistance; 3) bending, easy to install; 4) long service life.
3) The end thermal resistance end face thermal resistance temperature sensing element is made of specially treated resistance wire material and is close to the end face of the thermometer,. Compared with the general axial thermal resistance, it can reflect the actual temperature of the measured end face more accurately and quickly, and is suitable for measuring the end face temperature of bearing bush and other parts.
4) Through the junction box with special structure, the explosion of explosive gas mixture inside the shell due to the influence of spark or arc is limited in the junction box, and the explosion will not be induced in the production site. The flameproof thermal resistance can be used to measure the temperature in the area of BLA ~ B3c. This article originates from Zetian sensing Please keep the source.