jimbo39 wrote:Hi Tony,
With regard to what you said about the MAP sensor, I was going to have that on the depression side (motor side) of my test piece...I thought that would work OK
Maybe I was just being hopeful and my usual cheap@$$ self :p
What do most of you more experienced people use - digital manom or fluid? just curious
A very few people here that already have fluid manometers continue to use them.
But the Forum digital manometer is so vastly better, and has so many great features at such an affordable price, I don't think anyone starting out totally from scratch would ever consider going to the trouble of fabricating their own home made water manometers, it just is not worth the effort.
A MAP sensor would certainly work, and you could even use software driven solenoid valves to first measure atmospheric pressure, then measure pressure within the flow bench, and subtract the difference.
That is cumbersome, prone to errors creeping in, slow, and a real nuisance. But its possible.
Nobody ever does it that way when you can just buy a proper low dollar differential pressure transducer and be done...
Another thing to think about.
An absolute pressure transducer needs to operate against full atmospheric pressure, so you are measuring roughly 400 inches above perfect vacuum before you even start measuring test (or orifice) pressures, which are quite low in comparison.
In the Forum flow bench we use a 16 inch range differential transducer, which is going to be far more sensitive and less prone to drift and errors than maybe a 450+ inch absolute range sensor.
As far as flow measurement with an orifice plate goes, mother nature provides us with a perfect square law output of flow versus measured differential pressure drop across the orifice plate.
So its pretty easy to convert measured orifice differential pressure to exact flow in software.
That is the great power of the digital manometer, it reads out directly in CFM on your computer screen.
And you can order orifice plates from Bruce here at the forum to suit whatever measurement range you need.
It solves the problem of calibrating a home made flow bench very neatly.
With fluid manometers you need to use a pocket calculator or spread sheet to do the square law thing with every water manometer reading you take.
Its slow, but it certainly works and is accurate, just a real pain if you are going to be doing a lot of flow bench work.
Also known as the infamous "Warpspeed" on some other Forums.
) they both said well maybe lets see . . . 
I created an account in-case it was that but nope, can't purchase. 