(4) MADDAM
(a)
This portion of the computer converts ac and dc input information into digital form for computational use by the computer. Conversions are performed utilizing a Multiplexed Analog-to-Digital and Digital-to-Analog Multiplexed (MADDAM) technique. It also converts computed digital information into analog dc output signals. The technique used is the conversion of voltage to time, by the use of a linear ramp.
(b)
The CADC ac synchro input signals to transformer assembly board A12 are applied to the computer through isolation input transformers. An X-Z and Y-Z component of each synchro input is developed by the transformers. These components will ultimately be changed to digital numbers representing their voltage levels so synchro angle can be determined. The A12 board contains a voltage divider network for the program return low and program return high outputs; and level converters for the a/c pack 1=0, 2=0, 3=0 inputs. The board also contains an additional level converter for the aspirated probe discrete and decoder/driver circuit for providing signal lamp drive outputs to the auto throttle system which provide annunciation of the derating the computer is calculating.
EFFECTIVITY
LH 011-030,051-070,082-099;
AF 121-199; AZ 221-299; AND GN 601-699 AIRPLANES CONFIG 1 WITHOUT PMS 02 Page 12
Sep 25/94
34-15-00
(c)
The ac input module A11 contains two pairs of field effect transistor (FET) switches. One pair of switches is used for the X component and the other pair for the Y component of each synchro input. These synchro signals are applied to the switches which are controlled by separate logic circuitry synchronized to the synchro excitation voltage. The logic ensures the switches close at the exact time to pass only the peak value of the ac signal. This peak value is stored on separate holding capacitors, one for X and one for Y. Thus each synchro input is converted into a pair of dc voltages. Each pair of dc output voltages is updated every 10 ms.
(d)
The dc input to be converted is applied to the converter board A9 by the multiplexer board A10. The dc value of the synchro inputs from ac input board A11 and additional dc inputs such as TAT and mode are selected by FET switches in the multiplexer. The command channel of the I/O board instructs the FET switches on the multiplexer board to pass the dc values to be converted. These dc values comprise the X and Y signals to converter board A9.
(e)
The converter board A9 works in conjunction with the I/O board A7. A linear ramp generator drives one input each of two comparators. The other inputs of each comparator are switches, via FET switches, to either the negative computer voltage reference or the selected signal from the multiplexer board A10. The operation of each FET switch is controlled by the logic on converter board A9. Each comparator generates a pulse when the ramp equals the negative reference voltage and another pulse when the ramp equals the unknown dc input level. These pulses control the count time of the counters in the I/O, providing the digital numbers corresponding to the dc inputs.
(f)
After computations are made using the various digital and converted analog inputs, provision must be made for the necessary dc outputs. In doing a digital to dc conversion (D/A), the central processor presets channel 0 of the I/O board with the complement of the digital number to be converted. The ramp is then initiated and when the ramp equals the negative reference voltage the counter starts. When the counter is full the ramp stops. The ramp output level is applied into the regulator and dc output board A8.
(g)
The converter board also monitors various external and internally generated discrete signals to ensure and monitor proper system operation. Warning signals are produced by monitoring certain discretes if the system is not operating properly. The converter board supplies two voltage reference signals which are used to generate the program return low and program return high outputs.
EFFECTIVITY
LH 011-030,051-070,082-099;
AF 121-199; AZ 221-299; AND GN 601-699 AIRPLANES CONFIG 1 WITHOUT PMS 02 Page 13
Sep 25/94
34-15-00
(h)
The regulator and dc output board A8 provides the dc output signal circuits and the operating voltages for the analog sections of the computer. The dc output signals are obtained from the converter board and stored on holding capacitors. These dc values are then applied to the indicator to display the mode and N1 limit computed by the computer. These signals are updated each iteration. The regulators condition the unregulated power from the power supply PS1.
(i)
The N1 limit and computer mode input signals are applied to inverting amplifiers which amplify and invert the applied signals. When the amplifier outputs are positive, the motors drive the wiper arms of the follow-up potentiometers toward the positive dc supply. This positive potential cancels the negative input and the inverting amplifier outputs are reduced to zero. The motors stop driving the wiper arms and the counter shows the updated N1 limit and the selected mode.
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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(96)
