MAF sensor accuracy?
MAF sensor accuracy?
(OP)
I am finishing up on a pretty big CFM flow bench I am looking at possibly using MAF sensing to digitize the setup and drive a VFD through a PLC loop. I am kind of second guessing that whole idea. I killed the idea before for some reason I can now not remember.
If that will not do it, what would you guys reach for? Basically the system is running 2 8-71 helical lobe superchargers driven by a large motor and VFD estimated to pull approx 2000cfm at 28in.
If that will not do it, what would you guys reach for? Basically the system is running 2 8-71 helical lobe superchargers driven by a large motor and VFD estimated to pull approx 2000cfm at 28in.





RE: MAF sensor accuracy?
How many CFM is that EXACTLY, and how can you be absolutely sure ?
And what if the ambient temperature changes, how many CFM is it then ?
You do also realize that the MAF output voltage versus airflow is a hugely non linear curve.
RE: MAF sensor accuracy?
RE: MAF sensor accuracy?
Do it properly, build an orifice flow bench.
RE: MAF sensor accuracy?
RE: MAF sensor accuracy?
It also clogs and gradually loses accuracy over time.
A flow measurement orifice costs nothing, and always remains the same.
RE: MAF sensor accuracy?
They are effected by deposits (dust etc) so they need periodic cleaning (usually by "burn off").
The non-linear output is deliberate and beneficial (maintains % resolution) unlike orifice plates which have a pathetic turndown (they are non-linear in the wrong direction) - you need a few sizes and switching if you wan to cover a wide flow range.
My choice would be MAF, with an orifice or two to spot-check the MAF calibration from time to time.
Engineering is the art of creating things you need, from things you can get.
RE: MAF sensor accuracy?
RE: MAF sensor accuracy?
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RE: MAF sensor accuracy?
Without calibrating or checking with an orifice, closest you could get with a MAF sensor is to find the MAF table programmed in the vehicle's PCM. Use a common sensor (GM 85mm, LQ4) and average tables from multiple vehicles (they will have different intake ducting and slightly different values) if possible.
That sensor has a built in screen to straighten the inlet flow. Honeycomb a few mm thick so it does have a straightening effect, it's not just a round wire mesh screen.
RE: MAF sensor accuracy?
A series of screens or honeycombs spaced strategically apart can help somewhat with the latter, arguably at the cost of length, added complexity, and flow restriction (which may or may not be an issue).
RE: MAF sensor accuracy?
All hot wire anemometer can do is measure the air velocity in the exact physical vicinity of the wire.
If the flow profile is non laminar, or biased to one side, or surging, the hot wire will give a false reading.
RE: MAF sensor accuracy?
The two, of course, are related, but with the potential for nontrivial air density changes under normal operating conditions, they are not the same.
RE: MAF sensor accuracy?
You can certainly calibrate a particular hot wire sensor placed in a particular flow path, and this is routinely done in vehicles with some type of lookup table.
Provided absolutely nothing is changed, it may work reasonably well over a span of time during final engine tuning.
As one of the longest term members of the Flow Bench Forum, I can tell you that nobody there, and no commercial flow bench manufacturer uses a hot wire MAF for flow measurement.
The consensus there, is that a non corrected ratiometric measurement against a reference orifice plate is definitely the way to go for a flow bench.
RE: MAF sensor accuracy?
You can certainly calibrate a particular hot wire sensor placed in a particular flow path, and this is routinely done in vehicles with some type of lookup table adjusted during final engine tuning.
Provided absolutely nothing is changed, it may work reasonably well over a span of time.
RE: MAF sensor accuracy?
Warp, what is the easiest yet accurate way to digitally "sensorize" a flow bench? I am trying to stay away from analog stuff so I can capture and review test data.
RE: MAF sensor accuracy?
I suggest you check out the Flow Bench Forum.
There you will find many like minded people, most of them non wealthy enthusiasts, and a sprinkling of well known top professional "names".
Forum members from around the world have solved all the problems and built their own professional quality computerised digital flow benches for basically the cost of the materials.
It is by far the most friendly Forum to be found anywhere on the internet.
http://www.flowbenchtech.com/forum/
RE: MAF sensor accuracy?
RE: MAF sensor accuracy?
Regards
Pat
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