P.C.U. lever is operated to reverse the pitch of the propeller.
INSTRUMENTATION
9. The performance of the engine and the operation of the engine systems are shown on gauges or by the operation of flag or dolls-eye type indicators. A diagrammatic arrangement of the control and instru-mentation for a turbo-jet engine is shown in fig. 12-2.
图12-2 发动机控制和仪表的布置图
Fig. 12-2 Diagrammatic arrangement of engine control and instrumentation.
Controls and instrumentation
发动机推力
10．发动机的推力用推力计来指示。推力计有两种基本类型，第一种测量涡轮出口或喷管压力，第二种称为发动机压比(E.P.R.)表，测量两种或三种参数之比。当测量发动机压比时,该压比通常是喷管的压力与压气机进口压力之比。但是，对于风扇发动机来说,该压比可以是涡轮出口和风扇出口的综合压力与压气机进口压力之比。
14.发动机压比既可以由电机械式，也可以由电子式传感器来指示。对于这两种情况，传感器的输入是发动机的进口压力(P1)及由风扇出口压力和涡轮排气压力构成的综台压力(PINT)。有些情况下单独使用风扇出口压力或者涡轮排气压力取代PINT。
图12-3 电机械式发动机压比(E.P.R.)传感器
15.电机械式系统对压力改变的指示方式是采用传感器膜盒（图12-3）使压力传感器的中心轴偏移，导致轭架相当于A.A轴旋转。这一运动由线性可调电压差变压器感测，并转换成为交流电信号，经过放大后作用在伺服马达的控制绕组上。
Controls and instrumentation
16.伺服马达通过齿轮改变通向发动机压力比指示器的电位计输出低压信号，同时驱动平衡架沿着与轭架的原始运动相同的方向运动，直到通向马达的线性可调电压差变压器信号消失和系统稳定在新的位置为止。
17.电子式发动机压比系统采用两个震动筒式压力传感器，它们感测发动机空气压力，并在与这些压力相关的频率下振动。依据这些振动频率，计算出发动机压比的电信号，然后将信号输入发动机压比表和电子式发动机控制系统（第10章）。
Engine thrust the minimum thrust output can be checked under all
10.
The thrust of an engine is shown on a thrust-meter, which will be one of two basic types; the first measures turbine discharge or jet pipe pressure, and the second, known as an engine pressure ratio (E.P.R.) gauge, measures the ratio of two or three parameters. When E.P.R. is measured, the ratio is usually that of jet pipe pressure to compressor inlet pressure. However, on a fan engine the ratio may be that of integrated turbine discharge and fan outlet pressures to compressor inlet pressure.
11.
In each instance, an indication of thrust output is given, although when only the turbine discharge pressure is measured, correction is necessary for variation of inlet pressure; however, both types may require correction for variation of ambient air temperature. To compensate for ambient atmospheric conditions, it is possible to set a correction figure to a sub-scale on the gauge; thus,
operating conditions.
12.
Suitably positioned pilot tubes sense the pressure or pressures appropriate to the type of indication being taken from the engine. The pilot tubes are either directly connected to the indicator or to a pressure transmitter that is electrically connected to the indicator.
13.
An indicator that shows only the turbine discharge pressure is basically a gauge, the dial of which may be marked in pounds per square inch (p.s.i.), inches of mercury (in. Hg.), or a percentage of the maximum thrust.
14.
E.P.R. can be indicated by either electro-mechanical or electronic transmitters. In both cases the inputs to the transmitter are engine inlet pressure (P1) and an integrated pressure (PINT) comprised of
20.除了提供发动机的功率指示之外，扭矩计系统还在由于功率故障造成扭矩计滑油压力降低时，用于自动控制螺旋桨顺桨系统。对于某些安装条件下，它还用于协助喷水系统的自动操作，以便在外界温度较高或在高海拔飞机场恢复或增大起飞功率（第17章）。
图12-4 简单的扭矩系统
Fig. 12-4 A simple torquemeter system.
22.发动机转速指示由发动机驱动的一个小型发电机经电路传给指示器，它显示出实际的每分钟转速（r.p.m.)，或者显示出发动机最大转速的百分比（图12-5）。发动机转速常常用于估算发动机扭力。但是，由于进口温度和压力状态会影响给定的发动机转速下的推力，所以它给出的不是推力的 指示值。
发动机转速
21.所有的发动机都有它们的转速指示。对于双转子或三转子发动机，总是要指示高压转子的转速。在多数情况下，还有另外的指示器显示低压和中压转子的转速。
Controls and instrumentation
fan outlet and turbine exhaust pressures. In some cases either fan outlet pressure or turbine exhaust pressure are used alone in place of PINT.
15. The electro-mechanical system indicates a change in pressure by using transducer capsules (fig. 12-3) to deflect the centre shaft of the pressure transducer causing the yoke to pivot about the axis
A.A. This movement is sensed by the linear variable differential transformer (L.V.D.T.) and converted to an
a.c. electrical signal which is amplified and applied to the control winding of the servo motor.
16. The servo motor, through the gears, alters the potentiometer output voltage signal to the E.P.R. indicator and simultaneously drives the gimbal in the same direction as the initial yoke movement until the
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