ADIRS - Static Probe
Figure 004
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ADIRS - Pitot Probe
Figure 005
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C. Air Data Modules (ADM) (Ref. Fig. 006) The term Air Data Module (ADM) refers to any remotely located LRU which senses pressure information and transmits it to the ADIRU in ARINC 429 format. The ADMs are remotely mounted near and above the level of the pitot and static probes, this in order to make the ADM pneumatic plumbing self draining when the aircraft is stationary on the ground.
(1)
Internal description
The ADM comprises the following components
(Ref. Fig. 007)
(a)
Pressure sensor The sensor delivers a pressure frequency (Fp) signal and a temperature frequency (Ft) signal corresponding to the measured pressure.
(b)
Processor board The electronic card comprises the following circuits:
-a micro-controller 80C31
-two memories: ROM (storage of software program and pressure sensor modelling coefficients) and RAM (temporary storage of data)
-an ARINC 429 transmitter.
The processor board uses the Ft and Fp signals sent by the
pressure sensor and the sensor modelling coefficients stored in
the EEPROM to compute the pressure.
(c)
EMI/lightning board
This board comprises the following devices:
-power supply: the ADM is supplied by the associated ADIRU with +/- 13.5VAC. Power consumption is less than 200 mA on the +13.5VDC input and less than 40 mA on the -13.5VDC input.
-EMI filters
-lightning protection
-input discretes filtering.
(2)
Modes of operation
The ADM has two modes of operation:
-power-up
-normal operation.
(a) Power-up Two types of reset are available depending on the following conditions :
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Air Data Module
Figure 006
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ADM - Block Diagram
Figure 007
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1_ Complete reset The equipment performs a complete hardware and software reset cycle whenever the equipment is switched on or after a power cut greater than 100 ms. In this case, the equipment is fully operational after 2 seconds.
The complete reset includes all that is necessary to initialize the operation of the equipment : - initialize the RAM, variables, counters.
- tests :
* discrete input parity : After the 5 SDI discretes have been acquired, and position identification and parity checks have been made, the parity bits are checked to ensure that there is an odd number of
logic "1"s. * ARINC output : Two additionnal configurations are looped back, and the words thus received are checked bit by bit. * An algorithm requiring a significant number of instructions is run for the Arithmetic and Logic Unit test. * The internal RAM is checked by means of a write-read
sequence. - wait for sensor periods to be set and initialization of the pressure filter. - transmission on ARINC :
* no transmission during the reset hard (0.1 s) * transmission of discrete words with bits set to the pass condition
* transmission of pressure parameter : the Status Sign Matrix is set to Functional Test and the data is set to
zero.
2_ Modified reset
The equipment performs a modified reset after a power cut equal or less than 10 ms. In this case, the equipment is fully operational within 100 ms +/- 5 ms. The modified reset includes the following initializations : - initialize the RAM, variables, counters.
- initialize the pressure filter after 2 calculated pressure (30 ms). - no transmission on ARINC during this reset.
3_ The equipment performs either type of reset after a power cut greater than 10 ms and less than 100 ms.
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(b) Normal operation mode The ADM enters the Normal Operation Mode after the completion of the Power-up Mode. It remains in the Normal Operation Mode until either power is removed from the ADM, or an internal failure activates the Watchdog Timer, or an internal BITE detects an unsafe condition at which time a failure warning is annunciated or ARINC 429 transmissions cease. The ADM performs the following functions in the Normal Operation Mode:
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