ISFD Behaviour - CB & Screen Blank

[Roddez]

Hi Hardy,

We are working on a new solution for an ISFD display in a simulator.  This installation will have a dedicated 4" display that sits behind the ISFD panel.

Part of this installation is a requirement to remove power from the LCD screen when appropriate (eg. Cold and Dark)

Would I be correct in assuming that I could use Qi39="IsfdInitTime" to determine if the screen should be on or off?
If Qi39=0, turn OFF the screen.
If Qi39>0, turn ON the screen.

Finally, can you please confirm the expected behaviour when you pull the ISFD Circuit Breaker?

Many Thanks,

Rod.

[Hardy Heinlin]

Hi Rod,

yes, but a little bit more:

if >7000 then ON else OFF

Well, if it's just for your hardware power, you can also use lower values or even zero, I guess. PSX starts the display fade-in at 7001 anyway.

The ISFD is powered by its own battery which is charged by the main battery bus via B25 on P7. If you pull B25, you just deactivate the charger, not the entire ISFD. The ISFD is deactivated if DC bus 3 is unpowered, and if the BATTERY switch and the STANDBY POWER selector on the overhead panel are set to OFF. You may ask why it has its own battery anway. I can't remember at the moment. Maybe it's just for no-break power transfers as it uses a laser gyro rather than a mechanical high-RPM gyro.


Regards,

|-|ardy

[Roddez]

Thanks for the quick response Hardy.

I'll find a value between 0 & 7000 that works.  The screen takes a second or so to turn on and it will be nice to see it fade in.

Cheers,

Rod.

[John H Watson]

The ISFD has its own battery because it lasts far longer than the aircraft batteries. The designers realised that if the aircraft lost all generator power on a long oceanic sector, the main batteries wouldn't have lasted long enough to get the aircraft to an airport. I've forgotten how long.... 270 minutes?

The ISFD uses peizo-electric principles rather than laser gyros. I assume that is now what is in your average smart phone, but it was once top secret because the same tech is used in missiles.

The ISFD battery is wired to the battery switch because you need a way of turning off the power to the ISFD to stop its dedicated battery depleting.

[Hardy Heinlin]

it was once top secret

When was the secret revealed? If I recall correctly, there were some documents that mentioned "laser gyro". But I can't remember how old they were.

[John H Watson]

Rumour has hit that the secret was revealed when Boeing sold the 777 to China (and received a heavy penalty from the US Government for doing so). I'm sure they could reverse engineer the technology if they didn't already have it.