Pyrometers are available in two forms:
1) A device for measuring the temperature of the molten pool, including: a refractory mounting sleeve and an optical pyrometer;
2) Generally refers to the thermometer used to measure the temperature higher than 500℃. Commonly used pyrometers include optical pyrometers, colorimetric pyrometers, and radiation pyrometers.

The most commonly used optical pyrometer is the hidden wire optical pyrometer. There are two measurement methods: one is to adjust the resistance R to change the brightness of the filament. When it is equal to the brightness of the light source image to be measured, the filament disappears on the image of the light source. At this time, the brightness temperature of the object can be read from the meter G; or Use the compensation method to measure the accurate value of the current by the potentiometer, and then calculate the brightness temperature. The latter method is suitable for precise temperature measurement.
The second is to keep the brightness of the filament at a constant value, and rotate a piece of absorbing glass whose thickness changes with the angle. When the brightness of the object image is the same as the brightness of the filament, the brightness and temperature value of the object can be read from the corner of the absorbing glass.
The temperature indicated on the optical pyrometer can be determined using a standard temperature lamp.
The temperature of 700 ~ 3000 ℃ can be measured by using the hidden wire optical pyrometer. Higher temperatures can also be measured by replacing the bulb and the additional absorbing glass of the objective lens.