Engine Monitor PWM/ Frequency Inputs

[rv6ejguy]

Anyone know which popular brands can accept and process PWM/ frequency inputs from a digital device for fuel flow purposes?

 

[Dynon]

Ross,
For frequency, I think you'll find almost all engine monitors support a frequency input that will end up as fuel flow. Dynon's SkyView has 2 which can be used independently. Mechanical flow sensors are open collectors to ground so you can just pulse a transistor.

If what you really mean is PWM, where you hook to a fuel injector and measure the open time for fuel flow, that is much rarer. It also has many accuracy trade-offs like the variable latency that injectors have over voltage, meaning that you'd want your EMS to subtract some amount of the electrical on time because fuel isn't being injected.

Our experience on the Rotax 912iS is that you can only get accuracy to about 3% using the injector duty cycle (and this is with latency removed inside the ECM). While a mechanical flow sender is generally around 1/2%.

 

[rv6ejguy]

Ross,
For frequency, I think you'll find almost all engine monitors support a frequency input that will end up as fuel flow. Dynon's SkyView has 2 which can be used independently. Mechanical flow sensors are open collectors to ground so you can just pulse a transistor.

If what you really mean is PWM, where you hook to a fuel injector and measure the open time for fuel flow, that is much rarer. It also has many accuracy trade-offs like the variable latency that injectors have over voltage, meaning that you'd want your EMS to subtract some amount of the electrical on time because fuel isn't being injected.

Our experience on the Rotax 912iS is that you can only get accuracy to about 3% using the injector duty cycle (and this is with latency removed inside the ECM). While a mechanical flow sender is generally around 1/2%.

Thanks for the info.

I was referring to both frequency and PW signals as in the injector pulse train.

I believe we can correct for basic response time and latency due to voltage but the latter is not very significant with the alternator maintaining 14.2V +/- .2 or so.

The fuel density might have more effect I am thinking.