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Hi Gordon,
Way back around 2004, I developed an analog Fuel Totalizer
using the fuel injection pulse. It worked fine and was quite accurate,
however, it took something like 10 different analog chips (mainly counters
and dividers) and it had no memory for data storage, so if there was the
slightest electrical glitch, you lost your totalizer count.
Here was the concept I used - I built a simple pulse
generator that generator a pulse string so that the interval between these short
duration pulses was equal in time it took for four 450 cc/min fuel injectors to
flow 1/ 1,000,000 (that's right one millionth) of a gallon. Then
I gated this pulse generator so it would was turned on by the 13B injector
pulses. Then the system counted the small pulses that passed when
the fuel injector pulse was on and when it counted 1,000,000 of them
it totaled up one US gallon, when it had counted 2,000,000 pulses it rolled over
to 2 gallons - it incremented and kept track to 1/10 of a gallon.
Actually, 1/1,000,000 was a bit overkill, probably 1/1000
would have done just fine. This system also provided your fuel flow rate
as well.
I switched from the analog system to a digital system when
I finally realized that every significant change required a new analogy circuit
board - whereas with a digital chip doing it for me, I simply had to reprogram
the chip for any changes I wanted.
The first photo shows a comparison between the analogy and
my first attempt at the digital gadget. The digital version evolved to be
completely made with surface mount components and with a color display as shown
in the one labeled Christmas2007.
If you just wanted fuel flow, Tracy Crook provided a
very simple circuit which basically accumulated the voltage of the pulse duty
cycle in a capacitor and the voltage on the capacitor was directly proportional
to the duty cycle which in turn was proportional to the on/off time of the
injector pulse. Then a cheap volt meter measure the voltage on the
capacitor and you calibrated the circuit through trail and error until the
voltage shown on the digital voltmeter was equal to your fuel flow. Again,
it was very accurate, but did require a few flights to calibrate it and there
was no way to make it keep track of total fuel usage.
Hope this helps some
Ed
Sent: Saturday, April 20, 2013 3:58 PM
Subject: [FlyRotary] Fuel injector pulse frequency
All,
I'm looking at a DYI fuel
totalizer for a 13B using the fuel injector activation signal. I can't find
specifications that tell me the shape and frequency of the fuel injector pulse
and the number of pulses at each point in the engine RPM cycle. Can
someone point me to an authoritative source for this info?
Thanks in advance for any
leads.
Gordon C. Alling, Jr., PE
President
acumen
Engineering/Analysis,
Inc.
540-786-2200
www.acumen-ea.com
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