Optical pyrometer is generally used to measure

Explanation:

Optical pyrometer:

1. A temperature measuring device that is used to measure the temperature of molten metal’s, overheated material, furnaces otherwise liquids. It is one kind of measuring device of temperature with a non-contact.

2. The working principle of this optical pyrometer is to match the object’s brightness of the filament within the device.

3. By using contact type instruments, measuring the temperature of the highly heated body is not possible. So this non-contact type device is used to measure the temperature. Hence option (3) is true. 

Note: A remote-sensing thermometer that is used to gauge the temperature of a surface is known as a pyrometer.

Important Points

Advantages of Optical Pyrometer

1. The optical pyrometer has high accuracy.

2. The temperature is measured without contacting the heated body. Because of this property, the pyrometer is used for a number of applications.

Disadvantages of Optical Pyrometer

1. The working of the pyrometer depends on the intensity of light emitted by the heated body. Thereby, the pyrometer is used for measuring the temperature having a temperature more than        700-degree Celsius.

2. The accuracy of the pyrometer depends on the adjustment of the filament current.

3. Also, the pyrometer is not used for measuring the temperature of clean gases.

The applications of optical pyrometer include the following.

1. It is used to measure the temperature of highly heated materials

2. It is useful to measure furnace temperatures.

3. It is used in critical process measurements of semiconductor, medical, induction heat treating, crystal growth, furnace control, glass manufacture, medical, etc.