(2)
Transmission unit
(Ref. Fig. 005)
The transmission unit includes:
-a rotating transformer which serves to transmit the electrical energy (3125 Hz signal) from the fixed part to the rotating part to supply the electronic circuits and pressure sensor installed on the wheel. It also transmits the tire pressure value from the wheel to the axle. The value is given as an electrical signal with a variable frequency from 50 KHz to 100 KHz.
-an integrated electronic module which amplifies the signal from the sensor and changes the voltage into frequency (50 KHz to 100 KHz range) before the signal is applied to the transformer secondary winding.
(3)
Computer The 3 MCU computer is connected to the aircraft electrical wiring through an ARINC 600 connector, size 1.
B. Functions The functions of the systems are as follows:
-
It shows that the absolute pressure of any tire is lower than a given value,
-
It tells the flight crew when the pressure difference between 2 tires installed on the same wheel axle is above a given value,
-
It gives the pressure values of the 6 tires.
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Installation on Wheel - Block Diagram
Figure 005
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4. Operation/Control and Indicating
________________________________
A. Computer Operation (Ref. Fig. 006) The computer self-test is permanent and is only stopped for processing of the 3 functions below:
-pressure measurement,
-data distribution,
-maintenance.
A microprocessor performs these functions.
(1) Pressure measurement
The measurement channel is bi-directional:
-
transmission of electrical supply from the computer to the wheel,
-
transmission of pressure signal from the wheel to the computer. The computer gives a 3125 Hz signal transmitted cyclically to each of the six wheels to supply:
-
the wheel electronic module,
-
the pressure sensor. The pressure sensor supplies the voltage which is applied to a voltage/frequency converter. This converter gives a signal, the frequency of which varies from 50 to 100 KHz for a pressure excursion of from O to 300 psi. The pressure-representative signal is transmitted to the computer through a rotating transformer by modulation of the 3125 Hz carrier. To get the pressure measurement, you measure the duration of one period of the pressure-representative signal. The duration of each measurement cycle, for the wheels, is approximately 150 ms:
-15 ms for connection of the supply voltage,
-10 ms for the measurement ( 5 x 2 ms measurements max.). After you get the five successive measurements for one wheel, a digital filter serves to show the rate of pressure variation, i.e.:
-rapid decrease,
-3 measurements grouped in a limited interval,
-sawtooth measurement,
and to get a coherent mean pressure. Before the pressure value is sent to the lower ECAM DU, the computer makes a second read cycle. The computer then compares:
-
the last pressure transmitted to the users,
-
the pressure given by the two measurement cycles made before to discriminate the most significant value, function of the pressure variation.
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Tire-Pressure Indicating System - Block Diagram
Figure 006
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(2) Distribution of data The microprocessor distributes the data and transmits, through an ARINC 429 bus, three types of message:
-the pressure of each tire in psi,
-for each tire, a normal pressure signal or a warning signal,
-the status of each measurement channel (normal or faulty).
This information is sent to the lower ECAM DU.
(Ref. Fig. 007)
B. Nominal Pressures and Detection Threshold Nominal inflation pressures are given for the nose and main gear wheels. The pressures are wired on the rear connector (Pin programming). A 6 bit code:
-programs the pressure of each wheel,
-gives an adjustment range from 9 to 15 bars by steps of 2 psi (Approx.
0.15 bars) for the main wheels and from 8 to 11 bars for the nose
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