(2)
The error signal required to position the rebalance/feedback system is developed in the chopper (Ref Fig. 2). Computer input (the dc analog voltage) and the dc voltage picked-off the rebalance potentiometer are compared in a solid-state modulator and a 400-Hz signal representative of the difference between the two inputs is produced. This error signal is used to position the rebalance potentiometer to null.
(3)
A yellow OFF flag is held out of view by an energized solenoid which is controlled by a failure monitor as shown in Fig. 2. The failure monitor allows the flag to cover the readout counter upon sensing any of the following conditions:
(a)
Loss of 28-volt dc flag from air data computer.
(b)
Loss of DC analog voltage from air data computer.
(c)
Excessive null voltage in reposition/feedback system.
(d)
Loss of 20-volt dc reference from air data computer.
(e)
Loss of 26-volt ac instrument power.
C. The true airspeed indicator is powered from 115-volt ac flight instrument bus No. 2 through flight instrument transformer No. 6 and circuit breaker CADC 2, TAS IND on electronic circuit breaker panel P7.
D. Other than the circuit breaker on panel P7 controlling instrument power, the indicator has no external controls. Its operational modes are either on or failed as governed by the failure monitor.
3. Static Air Temperature Indicator (Fig. 1, Sheet 2)
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A. The static air temperature indicator provides a visual indication of static air temperature as computed by the central air data computer system. Static air temperature is read on a 4-digit, drum numerical counter from -99 to +50 degrees centigrade in 1-degree increments. The two left counter wheels display positive temperature and the two right counter wheels display negative temperature. The sign of the temperature being read masks the pair of wheels not in use. In case of system or indicator failure, a yellow OFF flag covers the readout counter.
B. Static air temperature indicator input is a DC analog voltage from an operational amplifier provided by air data computer No. 2. For computer description and operation, refer to 34-12-00, Central Air Data Computer System.
(1)
The instrument transforms a computer dc analog output into a visual indication. As shown in figure 3, the rebalance/feedback system slaves the numerical counter to a dc analog input from air data computer No. 2 such that the counter is providing a continuously variable readout of static air temperature.
(2)
The error signal required to position the rebalance/feedback system is developed in the chopper. Refer to figure 3. Computer input (the dc analog voltage) and the dc voltage derived from the rebalance potentiometer are compared in a solid-state modulator. The resultant signal is used to position the rebalance potentiometer to null.
EFFECTIVITY
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(3) A yellow OFF flag is held out of view by an energized solenoid controlled by a failure monitor as shown in figure 3. The failure monitor allows the flag to cover the readout counter upon sensing any of the following conditions:
(a)
Loss of 28-volt dc flag from air data computer.
(b)
Loss of dc analog voltage from air data computer.
(c)
Excessive null voltage in reposition/feedback system.
(d)
Loss of 20-volt dc reference from air data computer.
(e)
Loss of 26-volt ac instrument power.
C. The static air temperature indicator is powered from 115-volt ac flight instrument bus No. 2 through flight instrument transformer No. 6 and circuit breaker CADC 2, SAT IND on panel P7.
D. The indicator has no external control other than the circuit breaker on panel P7 controlling instrument power. Its operational modes are either on or failed as governed by the failure monitor.
4. Total Air Temperature Indicator (TAT) (Fig. 1, Sheet 2)
_____________________________________
A. The total air temperature indicator provides a visual indication of total air temperature as sensed by a total air temperature probe. Total air temperature is read on a three-drum numerical counter from -60 to +60 degrees centigrade in 0.1-degree increments. In case of indicator failure, a yellow OFF flag appears in a window on the instrument face.
B. Indicator input is a resistance from the total air temperature probe that varies as a function of total air temperature. For temperature probe description and operation, refer to 34-12-00, Central Air Data Computer System. Pilots' indicator input is provided by total air temperature probe No. 1 and flight engineer's indicator input is from probe No. 2.
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本文链接地址：747飞机维护手册AMM CHAPTER 34 - NAVIGATION 第34章导航1(76)
