Temperature instruments' types-part 1

Rosemount temperature transmitter's types

Rotary thermometer

The rotary thermometer is made of a coiled bimetallic sheet. One end of the bimetallic sheet is fixed, and the other end is connected with the pointer. Due to the different expansion degree of the two metal sheets, the crimp degree of the bimetallic sheet is different at different temperatures, and the pointer then points to different positions on the dial. The temperature can be known from the reading on the dial.

Semiconductor thermometer

The resistance change of semiconductor is different from that of metal. When the temperature increases, the resistance decreases and changes greatly. Therefore, a small amount of temperature change can also make the resistance change significantly. The thermometer made has high precision and is often called temperature sensor.

Thermocouple thermometer

Thermocouple thermometer is composed of two different metals connected with a sensitive voltmeter. At different temperatures, metal contacts will produce different potential differences at both ends of the metal. The potential difference is very small, so it needs a sensitive voltmeter to measure it. From the reading of the voltmeter, we can know the temperature.

Optical pyrometer

If the temperature of an object is high enough to emit a large amount of visible light, its temperature can be determined by measuring its thermal radiation. This kind of thermometer is called optical thermometer. The thermometer is mainly made of a telescope equipped with a red filter and a group of circuits with small bulbs, galvanometers and variable resistors. Before use, establish the relationship between the temperature corresponding to different brightness of the filament and the reading on the galvanometer. When in use, align the telescope with the object to be measured and adjust the resistance so that the brightness of the bulb is the same as that of the object to be measured. At this time, the temperature of the object to be measured can be read from the galvanometer.

Liquid crystal thermometer

The liquid crystal made of different formulations has different phase transition temperature. When it changes phase, its optical properties will also change, making the liquid crystal look colored. If liquid crystals with different phase transition temperatures are coated on a piece of paper, the temperature can be known by the change of liquid crystal color. The advantage of this thermometer is that it is easy to read, while the disadvantage is that it is not accurate enough. It is often used in ornamental fish tanks to indicate the water temperature.