音輪
驅動軸
轉速探頭
壓氣機厘
通向放大器和指示器
26. In addition to providing an indication of rotor speed, the current induced at the speed probe can be used to illuminate a warning lamp on the instrument panel to indicate to the pilot that a rotor assembly is turning. This is particularly important at engine start, because it informs the pilot when to open the fuel cock to allow fuel to the engine. The lamp is connected into the slatting circuit and is illuminated during the starting cycle.
Turbine gas temperature
27.
The temperature of the exhaust gases is always indicated to ensure that the temperature of the turbine assembly can be checked at any specific operating condition. In addition, an automatic gas temperature control system is usually provided, to ensure that the maximum gas temperature is not exceeded (Part 10).
28.
Turbine gas temperature (T.G.T.) sometimes referred to as exhaust gas temperature (E.G.T.) or jet pipe temperature (J.P.T.), is a critical variable of engine operation and it is essential to provide an indication of this temperature. Ideally, turbine entry temperature (T.E.T.) should be measured; however, because of the high temperatures involved this is not practical, but, as the temperature drop across the turbine varies in a known manner, the temperature at the outlet from the turbine is usually measured by suitably positioned thermocouples. The temperature may alternatively be measured at an intermediate stage of the turbine assembly, as shown in fig. 12-7.
29.
The thermocouple probes used to transmit the temperature signal to the indicator consist of two wires of dissimilar metals that are joined together inside a metal guard tube. Transfer holes in the tube allow the exhaust gas to flow across the junction. The materials from which the thermocouples wires are made are usually nickel-chromium and nickel-aluminium alloys.
30.
The probes are positioned in the gas stream so as to obtain a good average temperature reading and are normally connected to form a parallel circuit. An indicator, which is basically a millivoltmeter calibrated to read in degrees centigrade, is connected into the circuit (fig. 12-8).
31.
The junction of the two wires at the thermocou-ple probe is known as the 'hot' or 'measuring' junction and that at the indicator as the 'cold' or 'reference' junction. If the cold junction is at a constant temperature and the hot junction is sensing the exhaust gas temperature, an electromotive force (E.M.F.), proportional to the temperature difference
31.在熱電偶探頭處的雙金屬絲的接點是“高溫”或“測量”接點，而在指示器處的是“低溫”或“基準”接點。假設低溫接點處于恒溫下，而高溫接點正在感測排氣溫度，在電路中就會產生與兩個接點的溫度差成正比的電動勢(E.M.F.)，使指示器的指針移動。為防止低溫接點的溫度發生變化，影響指示的溫度，在指示器中或在電路內裝有一個自動溫度補償裝置。
33.溫度控制系統的輸出也可以用來提供一個短脈沖方式的信號，當這個信號被連接到一個指示器之后，它將以數字方式記錄發動機的壽命。當發動機工作在更高的溫度范圍時，脈沖頻率逐步增加，使后期型指示器以更高的速率記錄，從而將發動機或設備的壽命直接與工作溫度聯系起來。
34.熱電偶也可以安排用于排氣溫度指示和控制系統傳輸進氣道空氣溫度的信號，因而提供按進氣道溫度變化進行過補償的燃氣溫度讀數。一種具有進氣道空氣探頭的典型雙元件熱電偶系統示于圖12-8。
滑油溫度和壓力
35.對于發動機正確和安全工作來說，獲得滑油溫度和壓力的精確指示極為重要。溫度和壓力的傳感器和指示器示于圖12-9。
36.滑油溫度由裝在滑油系統中的溫度感測元件測量。溫度的變化導致電阻值的變化，進而相應地改變指示器的電流。指示器的指針按相當于溫度變化的幅度偏轉，這些由攝氏溫度表記錄。
32.熱電偶探頭可以是單元件、雙元件、或三元件結構。當使用多個探頭的情況下，探頭的長度是不同的，以便在燃氣流的不同位置測取溫度讀數，這樣得到的平均讀數可以比使用單個探頭（圖12-7）時提供的讀數更準確。
圖12-7 渦輪熱電偶的安裝
Fig. 12-7 Turbine thermocouple installation.
of the two junctions is created in the circuit and this causes the indicator pointer to move. To prevent variations of cold junction temperature affecting the indicated temperature, an automatic temperature compensating device is incorporated in the indicator or in the circuit.
低壓渦輪1級導向葉片
Controls and instrumentation
32.
The thermocouple probes may be of single, double or triple element construction. Where multiple probes are used they are of differing lengths in order to obtain a temperature reading from different points in the gas stream to provide a better average reading than can be obtained from a single probe (fig. 12-7).
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