GE Druck ADTS 405, Service Manual

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Druck ADTS 405 Service Manual
K171 Issue No. 1 Page 1-8
Power supply
6. The power supply unit is located in the electronics rack enclosed in a metal casing. Output from
the PSU supplies the rack with a n5V and ±15V and a semi-regulated 24V supply (regulated
with respect to +5V supply). The circuit automatically resets after an interruption caused by a power
failure.
Solenoid valves
7. All solenoid valves are of a similar type, spring-loaded to the de-energised condition. When
energised, the plunger moves against spring pressure to operate the valve. The principal valves are the
apply and release solenoids, these operate alternately to connect the manifold either to the pressure or
the vacuum connection from the pump generating and then holding the required pressure in the
manifold. The relative opening times of the two valves are determined by the error signal in the
controller PCB, thereby ensuring that the pressure in each manifold reaches an equilibrium at the
pressures appropriate to the altitude, speed, rate of climb or engine intake condition demanded at the
hand terminal. The valves also equalise air pressure to give a zero reading during a self-test routine
when the test system is isolated from the aircraft air data systems. Both channels have protection
valves controlled by the microcomputer, when energised the valves close isolating the test system
from the aircraft system.
8. The humidity sensors measure the humidity of the air for each manifold producing a voltage
signal proportional to the humidity. The voltage is amplified and corrected using stored calibration
data held in each controller circuit. The resulting voltage is used to correct the signal from the vibrating
cylinder pressure transducer.
9. The pressure input line is fitted with a filter and a 9 bar pressure regulator before it feeds the
manifold assembly. The vacuum input line also has a filter.
10. The principal components of the manifold assembly are two pneumatic manifolds (one for pitot
connection, one for static), together with their associated solenoids, pressure sensing transducers.
These components are mounted on the inside of the rack and are not accessible when the rack is
installed.