Fuel Temp Sensor

[Aeroman]

Hi, British Airways have a Fuel Temp Sensor switch marked A or B. This is fitted to the overhead panel in the maintenance switch area. Is it modelled in PSX?

[Hardy Heinlin]

Hi, I've never seen that option. Is it on all BA 744s?

[Aeroman]

Hi Hardy,  Thanks for your reply.  I can't confirm that but it is definitely on our aircraft G-CIVM. It's fitted between the Gen Field Reset and the EEC 1 & 2 Maint Panel whose channel select switches are labeled INOP for all positions however, you can select the power switches between Norm and Test. I don't know if this is an often used option? So the answer to my original question is no, therefore I don't need to wire it the interface. On a related subject regarding the squib test panel, what could I use as the power source for the test lights? I have them currently wired direct to 28V but would like them to only be available when the correct bus is live?

Cheers

Tom

[John H Watson]

Not fitted to all.

G-CIVE, G-CIVJ~IVP were excluded.

The switch just provides an earth to the "Main" Fuel System EICAS Interface card (FSEIC) powered by DC Bus 3 TRU. The "B" temperature sensor (in the #1 tank also) feeds data to the Main FSEIC card. The "A" temperature sensor feeds data to the "Slave" FSEIC card (also powered by TRU 3). The two cards talk to each other.
I think the Main FSEIC card then sends the chosen sensor data to the EIUs.



There is only one CB for both FSEIC cards (found in the MEC).

[Hardy Heinlin]

Thanks for the details. Hm, well, I don't think I'll add this option as there won't be any flight deck effect anyway. (In PSX there is a single common fuel temp value in all tanks.)

Re squib light power source. You may read the main battery voltage from here ...

Qi134="BatVoltMain"; Mode=ECON; Min=0; Max=2796;

... and read the CB contacts on P6 at H2 thru H6.

To cut the power for squibs 1 and 3, you need to pull H2.
To cut the power for squibs 2 and 4, you need to pull H3.

In PSX the squib light brightness won't fade with the discharging battery; it will just blank at 17 volt. The squib fading is actually on my todo list, but I forgot this particular detail over ten years ago :-)


|-|ardy


P.S.: Question for the fire bottle experts: What might be the minimum voltage to make a squib explode?

[John H Watson]

I don't think I'll add this option as there won't be any flight deck effect anyway.

I vaguely recall using the switch (just to see what happened), but I can't remember if I saw any momentary blanking during the switchover.

Question for the fire bottle experts: What might be the minimum voltage to make a squib explode?

I couldn't find any values in the manuals. All I know is that the squib test lamps have a high enough resistance NOT to trigger the squibs. I couldn't find the part number or specs of the test lamps, however. Common lamps like GE387's are said to trigger the squibs if they are fitted by mistake. I guess the proper test panel lamps have a higher resistance.

I don't know how universal squibs are, but I found this document for a Lockheed C-130 Hercules

https://www.lockheedmartin.com/content/dam/lockheed-martin/aero/documents/sustainment/csc/service-news/sn-mag-v11-v20/V18N1.pdf

Squib Electrical Data
Squibs are designed to detonate at a minimum
voltage of 18 volts and a minimum current of 1.5
amperes. A squib should not tire[sic] when a current of 0.5
amp maximum passes through it for 60 (+/- 10) seconds,
or when it is repeatedly checked for resistance with a
current of 0.2 amp maximum. It should be noted that at
least one vendor (Holex) recommends a maximum of
0.01 amp for repeated checks.

Measure the resistance through the squib, and then
repeat the test on the other fire bottle. Resistance should
be 1 (+/-O.15) ohm if the squibs are satisfactory.

18 volts appears in some of the squib test tables in the 744 maintenance manual, but I'm not sure if that's airplane voltage or voltage at the squib. Airplane wiring may be a few ohms, so may affect the voltage/current at the squib (especially if the squib resistance is only 1 ohm).

[Hardy Heinlin]

Aha, 18 v. So I guess that 17 v which I set in PSX was not a random number. It's just 18 minus some tolerance.

I'm just asking because I've connected the squib light power in my program code to the same CB output object which is used to detonate the associated squib, and whose power is "unusable" when the voltage drops below 17 v.

It's just cosmetics anyway, but the light should certainly be illuminated a little even below 5 v rather than extinguish completely below 17 v.

[Aeroman]

Many thanks to all those that replied to my enquiries much appreciated.

[Hardy Heinlin]

The squib light fade-out effect with the discharging battery is now available in PSX 10.166:

https://aerowinx.com/board/index.php/topic,4191.0.html


Regards,

|-|ardy