SM-6T-2-02 APOLLO MISSION SIMULATOR INSTRUCTOR HANDBOOK
Analog Inputs to PCM.
Analog inputs to the PCM-T/M are of two types: dynamic and nominal. The dynamic analog inputs are supplied by the computer through digital-toanalog (D/A) converters and are 0 to +5 volts d-c signals representing specific measurements normally made aboard the S/C. These are the analog signals which MSFN will monitor under normal mission conditions.
Nominal analog signals are generated by tying the output lines in the AMS peripheral equipment to +2.5 volts dc. The nominal analog signals are those not normally monitored by MSFN in an actual mission. By tying these lines to + 2. 5 volts dc, continuous zero readings in the PCM output pulse train are avoided.
The 320 analog signals, nominal and dynamic, received by the T/M fault control unit may be faulted or allowed to pass unhindered to the PCM-T/M unit. Of these 320 signals, 50 are fed through attenuators which lower their voltage levels to a range of 0 to +50 millivolts dc from their original 0 to +5 volts dc. These signals then simulate the low-level analog inputs to the PCM-T/M.
Bilevel Inputs to PCM.
Bilevel inputs to the PCM-T/M are also of dynamic and nominal types. The nominal bilevel inputs are tied indiscriminately to 0 to +6 volts dc so that some intelligence will appear on each input line to the PCM-T/M. The dynamic bilevel signals will be provided by the computer and represent simulated event occurrences within the S/C. The bilevel signals are routed through the digital bit output circuits to the T/M faulting circuit, and then on to the PCM-T/M. In the T/M unit the 224 bilevel input signals are sampled eight at a time, at specific intervals and treated as parallel-digital words. Each bilevel input may be faulted individually in the fault control unit.
Parallel-Digital Inputs to PCM.
Most parallel-digital words are provided to the computer through the digital word output circuits. These words will be in the form of multiples of eight parallel bits. Four parallel-digital words are fed into the PCM-T/M unit through the T/M fault control unit. Each of these words (two 16-bit, one 24-bit, and one 32-bit) may be faulted in its entirety by the fault control unit. One additional eight parallel bit word is supplied to the T/M unit by the UDL. This is the UDL verify word, and no provisions are made to malfunction it directly.
Serial-Digital Input to PCM.
The 40-bit serial-digital word from the S/C G&N to the PCM is simulated by the computer in the AMS. This signal is presently fed directly from the AMS computer to the PCM-T/M unit. There the serial-digital word is con¬ verted to non-return-to-zero format and integrated into the output pulse train. 2-
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