The total radiation pyrometer consists of a radiation-receiving element and a measuring device to indicate the temperature directly. In this unit a diaphragm unit along with a mirror is used to focus the radiation on a radiation on a radiant energy sensing transducer. The lens to transducer (a vacuum thermocouple or a thermopile) distance is adjustable for proper focus. The mirror arrangement has an advantage that since there is no lens, the absorption and reflection effects are absent.
The mirror type of radiation receiver shown in the fig.No.3.9 is so arranged that the image of the front diaphragm be focused on the thermocouple by the mirror. Therefore, the temperature measurements are independent of the distance of the target if the field of view is filled. Presence of any absorbing media between target and the transducer reduces the radiation received that therefore the pyrometer reads low. Substances like smoke, dirt and gases absorb radiation and therefore cause negative static errors. On the other hand presence of heat sources like hot gases, high temperature particles and flame cause the meter to read high.
The out put from a total radiation pyrometer whether amplified or not, is usually taken to a PMMC instrument, or to a self-balancing potentiometer. Digital displays are also being increasingly used. The output may be fed to a recorder for recording or to a controller for control purposes. Their range is 1200°C to 3500°C.
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