Fuel Totalizer inputs

[herkyjerky]

Anyone have any idea what kind of signal feeds the fuel totalizer on legacy fuel quantity systems? (Not the BF-Goodrich digital type systems)

The individual tank gauges do the work reading the capacitence probes, but they send a single wire signal to the totalizer.

My first guess was DC linear voltage since that is popular for those types of applications, but I can't find anything on haystack or the TO/specs that says what it is.

Thanks in advance!

(Trying to debug and read the signal for an international customer I'm working with at the moment)

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First, each flight deck fuel quantity indicator sends a one wire resistive signal to a relay. This signal is called the rebalance signal, I think. This relay is controlled by the SPR master switch. When the SPR master is off, the rebalance signal for each gauge goes to a summation unit. The summation unit, located in the left hand hog troth, has a pot for each tank signal that is adjusted during the totalizer calibration. Each of the pot output signals are added together. The output from the summation unit goes to the total fuel indicator. When you turn the SPR master switch to any other position than off the relay energizes and sends the rebalance signal to the SPR fuel gauges, so you can refuel the airplane and not have anyone in the flight deck. When the SPR gauges are working, the totalizer is inop and the "SPR ON" light on the fuel panel comes on. And that's it, I hope this sheds some light on the totalizer thing.

[herkyjerky]

First, each flight deck fuel quantity indicator sends a one wire resistive signal to a relay. This signal is called the rebalance signal, I think. This relay is controlled by the SPR master switch. When the SPR master is off, the rebalance signal for each gauge goes to a summation unit. The summation unit, located in the left hand hog troth, has a pot for each tank signal that is adjusted during the totalizer calibration. Each of the pot output signals are added together. The output from the summation unit goes to the total fuel indicator. When you turn the SPR master switch to any other position than off the relay energizes and sends the rebalance signal to the SPR fuel gauges, so you can refuel the airplane and not have anyone in the flight deck. When the SPR gauges are working, the totalizer is inop and the "SPR ON" light on the fuel panel comes on. And that's it, I hope this sheds some light on the totalizer thing.

Thanks! Now I just have to figure out the equivilent readings from those POTS and I should be in buisness. (After they are calibrated)

[NATOPS1]

It is voltage that is sent to the totalizer that then positions the indicator needle (positioned by an error voltage).

From the book

"Signal voltages from each indicator are sent to the fuel quantity totalizer."

(Simple answer)

These voltage inputs are added together and compared to a standard (through a resistor bridge// the potentiometers that are adjusted to read each tank individually) , any error voltage is amplified then applied to the totalizing indicator to indicate the total fuel level.

This is why errors in tanks (off scale HI or LOW or inaccurate readings or CB out) affect the total reading. As the voltage changes (reoprted as voltage from the individual tanks based on fuel level or malfunction) the total voltage changes (up or down) and varies the input to the totalizer.

[NATOPS1]

Thanks! Now I just have to figure out the equivilent readings from those POTS and I should be in buisness. (After they are calibrated)

The Pots are calibrated to each tank so the totalizer "knows" what a tank "looks like" so it can determine the fuel level in the tank at various levels.

It is not a set value.

Once calibrated and the tank gage is reading "correctly" the voltage output is "correct" and the pots are adjusted to make the totalizer read "corect".

If all tanks are calibrated then the totalizer Pots are adjusted it too will read correct.

As the fuel level changes the voltage output changes, the totalizer will "change" to read the total fuel on the aircraft.