Fuel Flow Meter

[cognos]

I suppose those small pressures can be passed through a mechanical actuator and amplified with another pressure sensing cell. But that would add hysteresis (present in all pressure measuring equipment) and possibly compound errors in the original measurement...

The way it's done in the trade is the pressure is converted to a milliamp measurement in an appropriately-sized differential-pressure-measuring cell (measures the diff in pressure between the high and low pressure sides of the orifice, independent of the actual pressures). This milliamp signal is what's actually measured and calibrated, not the pressures.

In the old days, the actual pressures were measured on either side of the orifice - sometimes by gauges, often by mercury-filled manometers(!) and then the flows would be calculated from a chart.

Your problem here is the pulsating nature of the flow, and it's small/low flow/low pressure nature.

The pulsation can be fixed with a check valve (to prevent backflow) and a surge tank. The rest of it is not lending itself to a cost-effective solution...

Here's a crazy idea... your injection pump is essentially a variable-volume reciprocating pump, yes? If you knew the pump volume at "rack closed", and at "WFO", and a few points in between, could you not connect some sort of positioner/variable resistor setup to sense rack position that could be run through a microprocessor to give you something like the fuel-injector scenario in a car?

Then:

(Rack position sensed = pump volume in mls) X rpm/2 = mls/minute

[dubbleUJay]

Cognos, thanks for the explanation. I see that electronic pressure sensor IC's are getting much more affordable these days and might incorporate one of those in the future, alas, I can get one for that low pressure!

Believe it or not I did look at the pump rack in that way, but I wasn't sure how accurate it would be, even using the control rod into the pump, there's some "lash" in the gearing and mine seems to constantly move in & out all the time with a constant load on the engine. (I'm not sure if this is normal and I was going to address this in a new thread in the future, but my pump was refurbished by a shop that's suppose to know what they're doing!)
The cct in a PC mouse would read the movement quite accurate though!

[PROFG]

HELLO
Did this project just die - any updates on what worked?  Will go with the IV type since I have a few from last "care giver visit".
Dick

[ndavid79]

Sorry I dropped off the project guys.. Right after the water test, my supply company decided to go assain & hold my next shipment of formula (which we had a surplus of) & feed bags (which is impossible to form much of a surplus due to various issues with said company) hostage for 2 weeks over a billing issue that was their fault (they decided to forgo properly filling out claims to my 2 insurances, build up a bill & then ask for a CC#)... So hadda use that last old style bag (the kind w/ drip chamber) when the last new style bag (read cheap) sprung a leak after 3-4 days reuse.