Fuel flow question

[spudlyhallam]

My engine has a ecu which gives a fuel flow figure from the injection system but it is a different format to the dynon input can anyone help on how to convert it?
From my engine manual
The output signal is a duty signal.100% is equal to a fuel consumption of 12.7 us gal/hour
From the dynon manual
Enter the pulses/ per gallon
Any ideas?

 

[dynonsupport]

You cannot use that kind of signal with Dynon engine monitors. You need to convert that to a frequency output somehow. It is possible to build a circuit to convert from duty cycle to frequency, but I don't know of any commercial products that do this.

 

[spudlyhallam]

Ok but I am getting a reasonable reading it just needs tweaking
If the dynon reads the signal there must be a conversion factor?

 

[dynonsupport]

We read frequency and expect it to vary as fuel flow varies.

A duty cycle system has a frequency, but the frequency means nothing about the fuel flow. In the case of your configuration, the frequency is actually the RPM! You'll get exactly the same fuel flow at 2500 RPM every time. So it sort of looks reasonable because it goes up as RPM goes up, but technically has nothing to do with fuel flow.

There is no way to make this work with just adjusting the K value or with any other conversion factor. This is the difference between frequency and volume in music. There is no way to have a system that is designed to only listen to frequency report volume instead with just a conversion factor. It requires new software or hardware to make it work.

 

[spudlyhallam]

Hmmmm not the answer I was hoping for
I can't change the engine so do you think dynon will upgrade the ems to accept duty cycle?

 

[dynonsupport]

It is something that is theoretically possible for us to change, but we have not had enough interest so far to do so.

You can always add a mechanical fuel flow sender like most aircraft use.

 

[spudlyhallam]

The problem with a mech fuel sender is that with fuel injection the fuel is in a circuit and only some of it goes to the injectors with the rest going back to the fuel tanks that is why the ecu has a fuel flow output.
It is a shame the mgl infinity efis has duel inputs and the dynon has a single non duty cycle input.
Go on can you write some code for the next update

 

[dynonsupport]

We support two fuel flow inputs in SkyView, one for outgoing and one for return.