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Newer technology has provided electronic circuits and detectors that allow non-contact infrared sensors to be used to measure temperature. It's important to understand that all objects emit energy if their temperature is above absolute zero. The amount of energy increases as the temperature of the object increases. Fig. 1 shows a picture of a typical infrared temperature-measuring device. The sensor is mounted in a hand-held instrument whose physical appearance is similar to a gun.
Above: Fig. 1 Hand-held infrared pyrometer.
The gun is used by pointing it at the heat or energy source and reading the amount of energy emitted by it. This type of temperature-measuring device is required where non-contact measurement is necessary because of moving parts or where the part may be contaminated if a temperature probe is placed directly on it.
Fig. 2 shows a block diagram of the operation of an infrared pyrometer. The pyrometer receives light waves that are emitted from a source whose temperature lure is being measured. When the lens of the pyrometer is focused on the part being measured, the emitted light waves are received by the detecting circuit. The signal from the detector is sent to an op amp where it's amplified. The output from the op amp can be sent directly to a meter movement or display to indicate the amount of heat, or the signal can be sent to a signal conditioner where it's converted to a 4-20 mA or 0-10 volt signal that is useful as the process variable signal for controllers and recorders.
Above: Fig. 2 Block diagram of an infrared pyrometer.
