Optical Pyrometer Definition: The optical pyrometer is a non-contact type temperature measuring device. It works on the principle of matching the brightness of an object to the brightness of the filament which is placed inside the pyrometer. The optical pyrometer is used for measuring the temperature of the furnaces, molten metals, and other overheated material or liquids. It is not possible to measures the temperature of the highly heated body with the help of the contact type instrument. Hence the non-contact pyrometer is used for measuring their temperature. Construction of Optical Pyrometer The construction of the optical pyrometer is quite simple. The pyrometer is cylindrical inside which the lens is placed on one end and the eyepiece on the other end. The lamp is kept between the eyepiece and the lens. The filter is placed in front of the eyepiece. The filter helps in getting the monochromatic light. The lamp has the filament which is connected to the battery, ammeter and the rheostat. Working of Optical Pyrometer The optical pyrometer is shown in the figure below. It consists the lens which focuses the radiated energy from the heated object and targets it on the electric filament lamp. The intensity of the filament depends on the current passes through it. Hence the adjustable current is passed through the lamp.