With the resurgent interest in the TLs and their possible failure. I checked back to see where the electronic explanation was given. There are more posts, as well as the diagrams of the physical layout but this is about the electronic layout. To the outsider (me) who spent 25 years in IT, this looks like they have covered the eventuality of mechanical failure and ensured that it can be picked up by electronic means, which are themselves heavily duplicated.
TyroPicard #884
There are two Angle sensors on each Thrust Lever. If the two sensors disagree about the TLA, on the ground, but not at TOGA or FLX/MCT (i.e. take-off thrust setting), the FADEC selects Idle thrust irrespective of thrust lever position. An ECAM warning occurs and as part of the drill the pilot backs this up by selecting idle.
If neither sensor produces a valid signal, on the ground, the FADEC selects Idle thrust. An ECAM etc......
TripleBravo #1474
The position information is transmitted by 6 cables per sensor, which allow to cross-check for cable breaks and potentiometer breakups for each sensor. These analog signals are fed into one channel of FADEC (A), the other 6 from the second sensor are treated completely separate in channel B. The arbitration between the two FADEC channels takes place after input check and evaluation of the signals. Each channel is capable to control the engine on its own if the other fails. They are independent, also physically, which means that every chip is only responsible for one of the two channels.
Once again, this is no cheapo hardware like just one microcontroller doing all the math, so there is no need for such constructions like IRQs.
The engineering is well aware of the importance of treating these things right. Also the test departments are very creative inventing scenarios the engineering departments might have overlooked, kind of competition. Trust me, I have worked in that business, although not especially on thrust levers and engines.
vapilot2004 #1510
Airbus thrust lever description
The mechanical thrust controls for the A320 consists of three main parts:
The Levers,artificial feel units and control units.
This setup is common for most FADEC equipped aircraft with the only difference between Airbus A320/330/340 and others is the addition of a servo motor to back drive the throttle levers in autothrust mode.
Each thrust lever is connected by a pushrod to the input of an artificial feel unit. This unit provides friction and the detents throughout the motion of the thrust levers.
The artificial feel unit's output shaft is connected to the thrust control unit via a second pushrod. Within each thrust control unit are 6 potentiometers and 2 thrust angle resolvers.
The pots provide thrust lever position to the flight control system while the resolvers are dedicated to the engine thrust control.
A resolver is a sort of rotary transformer that outputs sine & cosine waves corresponding the the thrust lever angle. The mechanical ratio of the thrust lever angle and the resolver angle is 1:1.9. For every degree of movement of the levers, there is a 1.9 degree movement indicated by the resolver. Resolver units are more accurate and reliable in translating angular position data than potentiometers and is the reason for their use here.
Each thrust control unit has two resolvers - one for each EEC channel. A disagreement of more than 15' (1/4 degree) causes the EEC to go into resolver failure mode.
Each EEC also checks the resolver output for upper and lower limits. For the IAE engines the limits are from -41 to 88 degrees. Any value outside of these limits will cause the FADEC system to transfer engine thrust control to the alternate EEC.
Outside of a jammed feel unit or thrust control unit, a failure of the A320 manual thrust control system seems unlikely.