Misunderstandings in the application of bimetal thermometers
2022-10-08
Bimetal thermometer is a field detection instrument for measuring low and medium temperature. The instrument is made of two metals with different temperature expansion coefficients to make a thermal conductivity sensor, which makes full use of the principle of thermal expansion and contraction. The coil is rolled up or loosened because one end of the spiral coil is fixed and the other end is connected to a pointer that can rotate freely.
Therefore, when the bimetallic piece feels the temperature change, the pointer can indicate the temperature on a circular graduation scale. The temperature measurement range of this bimetallic thermometer is -40~550℃, and the allowable error: ±1.6 degrees . This creates the following two misunderstandings:
1. High temperature range
The temperature measurement range of the bimetal thermometer is 200~650℃ (also clearly recorded in Baidu Encyclopedia), and the allowable error is about 1% of the scale range. In fact, this is wrong, because this kind of metal sheet is made into a spiral-shaped thermal conductivity sensor, which is easy to fatigue at a high temperature of 650 °C, and the temperature difference is very large, so when the temperature exceeds 550 °C, you should consider using a thermocouple to solve this problem. question.
2. Minimum temperature range
Therefore, when the bimetallic piece feels the temperature change, the pointer can indicate the temperature on a circular graduation scale. The temperature measurement range of this bimetallic thermometer is -40~550℃, and the allowable error: ±1.6 degrees . This creates the following two misunderstandings:
1. High temperature range
The temperature measurement range of the bimetal thermometer is 200~650℃ (also clearly recorded in Baidu Encyclopedia), and the allowable error is about 1% of the scale range. In fact, this is wrong, because this kind of metal sheet is made into a spiral-shaped thermal conductivity sensor, which is easy to fatigue at a high temperature of 650 °C, and the temperature difference is very large, so when the temperature exceeds 550 °C, you should consider using a thermocouple to solve this problem. question.
2. Minimum temperature range
The temperature range of the bimetal thermometer is 200~650°C (this is incorrect), and the lowest temperature can be measured to -40°C. In fact, this is not much, because the temperature calibration of bimetal thermometers in production is usually -20 °C (if low temperature is required, if not, we usually mark 0 °C to the upper limit of the temperature required by the customer, in Beijing Fang District Users sometimes use -40°C, this can be done, but in the case of -40°C, it is necessary to consider whether the error can be accepted.
