Minggu, 08 Mei 2011

Temperature Sensors - Replacement Time Again?

When people in the office talk about temperature sensors they are almost certainly talking about part of a car emission control system. The engine control system adjusts the fuel and air-flow to the combustion chambers of an internal combustion engine depending on its temperature. If the temperature sensor is faulty, then the engine will not run correctly, if it runs at all. Older drivers may remember the manual choke control that you pulled out to start the engine when it was cold, and how this was superseded by the automatic choke. Somehow the manual choke never went wrong, unlike its new and allegedly better replacement. Temperature sensors are one of the most frequently replaced parts in an automobile. Temperature sensors away from the world of motoring are designed to measure the temperature at different stages of a chemical or other industrial process and feed back that data to a control center. Pyrometers are specialist temperature measuring devices with a very fast response time and a very high operating temperature range. Pyrometers may have a response time as low as 5 milliseconds and can measure the temperature without contact with the material. These features mean that a pyrometer is essential where a manufacturer wants to measure the temperature of a rapidly moving steel rod or even of a molten steel stream. A pyrometer works by analysing the thermal radiation emitted by a hot object. All black bodies emit radiation of the same frequency at the same temperature. An optical pyrometer the frequency emitted by an electrically heated filament is matched with the frequency of the radiation emitted by the hot object/material under test. When the two match they are the same temperature. The temperature of the filament is obtained by referring to tables of data and operating conditions. In a radiation pyrometer the radiation emitted from the object/material under test is detected using sensor such as a thermocouple.

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