Fuel transfer monitor

[paul330]

I am looking to try and devise a system that will monitor transfer from aux fuel tanks. Initially, it's easy enough. You use a sender (5v typically). You configure a GP port to give Green with voltage above 2.5v and yellow warning below 2.5v, prompting you to switch off the transfer pump. The only problem with that is that once switched off, the voltage is still below 2.5v and the warning remains.

How can you disable the warning (and black out the display) if the switch is off? The only thing I can think of at the moment is to use a ON-ON switch and feed 12v and then use resistors to mess with the voltages so I can get a Green/Yellow/Black indication. There must be an easier way......

 

[dynonsupport]

Paul,
Are you using a sender that is just a switch, or one that varies with the level in the tanks?

What exact behavior do you want? Something like this:?

1) Black when switch off (or green?)
2) Green when switch on and level high
3) Yellow when switch on and level low

Or are you trying to see the level in the tank all the time?

In my plane, I have aux tanks with level senders and pumps. I have the pumps wired up to show yellow on the screen when on and black when off. I just set a timer whenever I turn them on, and when the timer expires I turn them off. They take about 20 minutes to transfer so it's easy to forget. The advantage here is that I can see the levels in the tank all the time.

Anyway, let us know what you want and I bet we can come up with a simple answer.

 

[paul330]

Sorry to be so vague - still at the initial planning stage and looking what to order....

I want to transfer fuel from an aux to main tank using a low pressure Facet pump.  There is no gauging of the aux tank so I want to know when it is empty.  My plan is to use a Kavlico carb fuel pressure sender (or similar unit).  At full pressure, this outputs 5v (I believe) so it would be easy to monitor when the pressure falls and bring up an alarm.  However, once the pump is switched off, the pressure is still low so the alarm would continue.

The behaviour I want is thus:

- pump ON and fuel transferring - pressure high - Green
- pump ON and fuel empty - pressure low - Amber
- pump OFF - Black

So the issue is how to differentiate between (pump switch ON, pressure low) and (pump switch OFF - pressure low).

 

[dynonsupport]

Paul,
What pressure are you monitoring? I'm not sure there's any pressure in that system to monitor.

Assuming there is, then I think the answer is easy. You need a DPST or DPDT switch (two switches in one) The Kavlicos are 0.5 to 4.5V, not 0 to 5V. So if you run the Kavlico signal through your switch, then when the switch is ON, you'll get somewhere between 0.5V and 4.5V, and you can set up colors for that. When the switch is off, you'll get 5V (the EMS pulls up to 5V), and you can set 4.5V to 5.0V up as BLACK.

Then run the Facet pump through the other side of the switch.

This is in fact exactly how I have my plane set up, except I use the second side of the switch to just tell the EMS if the pump is on or off, not to control a signal, but it works the same.

 

[paul330]

OK - I had some sort of idea like that.  I was planning to use a DPDT ON-ON and feed 12v to the "OFF" side to fool the EMS......

Just to be sure.....

I am trying to measure the fuel pressure in the transfer line from the aux to main tank.  When the fuel is transferring, it should be about 3psi so there will be a voltage between 05 and 4.5 v from the Kavlico sensor.  When the aux tank is empty, the pressure will drop to zero so (presumably) the Kavlico output will drop to 0.5 volts. If I disconnect the sensor using a switch then the GP input will sense 5V. Correct?