【導讀】TT302溫度變送器接收毫伏輸出的信號，這類傳感器包括熱電偶或阻性傳感器，它所接受的信號必須在允許的輸入范圍之內。為-50到500，電阻范圍為0到2021歐姆。多路轉換器將變送器端子接到相應信號調理板上，以保證在正確的端子上測量電壓。A/D轉換器將輸入信號轉換成數(shù)字形式傳給CPU。他的作用在輸入和CPU之間隔離控制信號和數(shù)字信號。CPU是變送器的智能部分，主要完成測量，板的執(zhí)行，自診斷和通信的管理和運行。斷電立即消失，所以數(shù)據(jù)必須保存在不易丟失的EEPROM中。監(jiān)視在線動態(tài)，調整通信信號，插入，刪除預處理，濾波。變送器電路通過現(xiàn)場總線電源供電。從CPU接收數(shù)據(jù)送給LCD顯示器的顯示部分，此時顯示器必須處于打開狀態(tài)。熱電偶由兩種不同的金屬或合金在一端連接在一起所組成的，被稱為測量端或熱端。TT302可以自動進行補償。TT302允許二線制連接，但可能會引起測量誤差。低的煙溫區(qū)，在部分過熱后，蒸汽進到二級過熱器而完成其過熱過程。

　　

【正文】 mum ash and slag deposits will result. Modern superheaters have many tube passes, and the tubes are arranged inline rather than staggered. The tubes are usually cylindrical and have 5 or outside diameter. There is no extended surface()attached to the tubes. The material selection depends on the steam temperature and pressure. Carbon steel has an allowable temperature up to 430℃ and is frequently used for loetemperature superheaters. Chromemoly, stainless steel, or same similar heat resistant alloy can withstand the temperature up to 650℃ . Therefore they are selected for the Superheater in a hightemperature zone. Temperature regulation and control are importation for both superheaters and reheaters. Steam temperature adjustments are frequently made at the time of the missioning of a boiler. The principal methods are an addition or regulating the hot gas temperature and mass flow rate. These are generally acplished by changing the excess air or the effectiveness of the evaporation section. During a boiler operation, there are many factors affecting the temperature of steam leaving the superheater and reheater. These include a boiler load, excess 15 air, feedwater temperature, and cleanliness of heating surfaces. Control of steam temperature during operation must be done without changing the arrangement of equipment. The most effective approaches are gas bypass, burner control, attemperation, gas recirculation, excess air, divided furnace. A gas bypass is to control the gas flow rate to superheater. The main disadvantages of this approach are the operating difficulties experienced by the movable dampers located in the hightemperature zone and the slow response to load change. Burner control is used to control the flame location and bustion rate. Tilting burners can direct the flame toward or away from the superheater. These will result in a change of heat absorption in the furnace and change of gas temperature in the superheater. As the boiler load is reduced, burners are removed one by one from service. This will change the bustion rate and, thus, change the gas flow rate to the superheater. Attemperation is one of approaches frequently used. The attemperator is usually located at the point between the primary and secondary superheaters. There are two basic types of attemperator. The first is the tubular type in which some of superheated steam is passed through the tubes of a heat exchanger and has heat transferred to the boiler water(either boiler feedwater or water in the boiler drum).Subsequent to attemperation, the divided streams from the primary superheater will bine and enter the secondary superheater. The second type of attemperator involves a spray of feedwater into the atream ofsuperheated steam. The feedwater evaporates and reduces the steam temperature. Controlling the amount of feedwater will result in control of the ateam temperature. Care must be exercised to ensure that the spray water has sufficient purity. The spray water should mix well with the superheated steam so that there are no water droplets in the inlet of the secondary superjeater. Gas recirculation is used to control the steam temperature by changing the heat absorption rates both in the furnace and in the superheater. When the ateam temperature needs to be raised, some of the furnace. Therefore, the furnace temperature will bee lower, resulting in a lower heat absorption in the furnace and thereby a higher flue gas temperature in the furnace exit. This high gas temperature, bined with an increase in the gas floe rate, will increase the heat transfer rate in the superheater and thus increase the steam outlet temperature. Temperature control can be affected bu using different amounts of excess air. the more the excess air, the higher the steam outlet temperature would be. The reasons for this are similar to those for the gas recirculation method. It must be pointed out, however, that too much excess air will result in a reduction of boiler bustion efficiency. A dividedfurnace boiler is usually arranged with a generation of saturated steam in one section and a superheating of steam in another section. The temperature of the superheated steam is regulated by controlling the firing rates in the two furnaces. This method is not economical and is seldom applied in a central electric power station. 16