音轮
驱动轴
转速探头
压气机厘
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.在热电偶探头处的双金属丝的接点是“高温”或“测量”接点，而在指示器处的是“低温”或“基准”接点。假设低温接点处于恒温下，而高温接点正在感测排气温度，在电路中就会产生与两个接点的温度差成正比的电动势(E.M.F.)，使指示器的指针移动。为防止低温接点的温度发生变化，影响指示的温度，在指示器中或在电路内装有一个自动温度补偿装置。
33.温度控制系统的输出也可以用来提供一个短脉冲方式的信号，当这个信号被连接到一个指示器之后，它将以数字方式记录发动机的寿命。当发动机工作在更高的温度范围时，脉冲频率逐步增加，使后期型指示器以更高的速率记录，从而将发动机或设备的寿命直接与工作温度联系起来。
34.热电偶也可以安排用于排气温度指示和控制系统传输进气道空气温度的信号，因而提供按进气道温度变化进行过补偿的燃气温度读数。一种具有进气道空气探头的典型双元件热电偶系统示于图12-8。
滑油温度和压力
35.对于发动机正确和安全工作来说，获得滑油温度和压力的精确指示极为重要。温度和压力的传感器和指示器示于图12-9。
36.滑油温度由装在滑油系统中的温度感测元件测量。温度的变化导致电阻值的变化，进而相应地改变指示器的电流。指示器的指针按相当于温度变化的幅度偏转，这些由摄氏温度表记录。
32.热电偶探头可以是单元件、双元件、或三元件结构。当使用多个探头的情况下，探头的长度是不同的，以便在燃气流的不同位置测取温度读数，这样得到的平均读数可以比使用单个探头（图12-7）时提供的读数更准确。
图12-7 涡轮热电偶的安装
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.
低压涡轮1级导向叶片
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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