Does FP1 require Temp option for Pitot bench

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RL
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Does FP1 require Temp option for Pitot bench

Post by RL »

I sent a email to FP1 and they say I need the temp sensor option for a pitot bench, but I don't see one on there Low cost flowbench(maybe it's not pictured)

I want to run in this order 1 test piece, 2 pitot ,3 motor, but when I test exh the hot motor air runs back up the bench

Did everyone with a pitot bench take the temp option or is there a way around it

By the time I option everything the price will double, can I use a thermocouple($20) as ther sensor is expensive

Thanks
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Post by shawn »

He didn't say anything about needing one for my bench, but now i wonder. I know with a L.F.E. requires constant adjustment for air temp, but i hadn't heard that about a pitot.
shawn
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gee, now you've got me thinking...

Post by fasteach »

i never got one with my package either, but that wa a few years ago...maybe this is new? i understand there's a weather station in the works, maybe this is part of it?
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Post by supebike »

I did not get one with mine either. I just bought the fp1 and fitted my own home made pitot tube into a bit of pipe. Its repeatable i can take the same head out of the cupbord on anyday sun/rain and still get the same results.
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Post by shawn »

Here's the answer I got back from John-
Hello,

If your air source is located between the test piece and the measuring device (orifice, Pitot), you will need temperature compensation. This is a non-ratiometric configuration, and is called a "center blower" bench design. The reason is because the air temperature is not the same when it passes through the test piece and measuring device.

In a ratiometric bench, the air that passes through the test piece will pass through the measuring device at about the same temperature, temperature compensation is usually not required (LFE the exception).

If you want to experiment with air density, you can set the temp and baro on the FP1 and read data column 3. But you will probably notice much more consistant readings from bench to bench, test to test, by ignoring the temp and baro settings and just using data column 4, which is calculated using a standard air density.

Short answer if you are using an FP Basic system in the standard configuration, is no, you should not need a temp sensor.

Hope this helps. Let me know if not.

Thanks

John
shawn
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Post by fasteach »

excellent news...quite typical of John to not only know and understand the situation, but to freely explain it in layman's terms to all who care enough to ask.
if i was in the market for flowbench equipment today, i'd still buy any of his fine products. class act all the way around.
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Post by RL »

This is part of the first email
For most flow bench systems it is not essential. Some benches have a center located motor where the air temp is different from test piece to measuring device, and a compensation is needed, but for a ratiometric bench, where the air is passing through a test piece and the flow measuring device at the same air density, a compensation is usually not needed. If the air passing through the ratiometric bench is changing rapidly, a compensation might be required.

In non-ratiometric systems (a Pitot tube on an airplane or race car) the air density needs to be accounted for.
I may be confused as to what a Ratiometric bench is. I thought a Orifice bench is ratiometric and a pitot is non-ratiometric

The 2nd email
In a ratiometric bench, the air that passes through
the test piece is about the same temp as when it
passes through the flow measuring device. In this
case, the density of the air is not critical for a
couple reasons.

In a non-ratio metric bench, the air is not the same
temp when it passes through the test piece and then
measuring device. The air density needs to be
determined and compensated, it is much more critical
for non-ratiometric benches.

When blowing hot air through any flow bench for
exhaust testing, you should do your exhaust testing
first, and quickly before the air gets too hot. With
hot air blowing through the bench, you have other
issues to consider besides air density, but air
density is not critical in a ratiometric setup
Since no one got a temp sensor with their Low cost flow bench kit it must be ratiometric
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Post by RL »

I also wonder when running exhaust, the hot air from the motors will heat my pipe(steel exh pipe for me) where the pitot will be , which will expand it to a bigger diameter , which will slightly slow the velocity, but the holes in the pitot will expand

Do I have to have the same temps between tests to compare them

Is everyones exh figures repeating
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Post by larrycavan »

RL wrote:This is part of the first email
For most flow bench systems it is not essential. Some benches have a center located motor where the air temp is different from test piece to measuring device, and a compensation is needed, but for a ratiometric bench, where the air is passing through a test piece and the flow measuring device at the same air density, a compensation is usually not needed. If the air passing through the ratiometric bench is changing rapidly, a compensation might be required.

In non-ratiometric systems (a Pitot tube on an airplane or race car) the air density needs to be accounted for.
I may be confused as to what a Ratiometric bench is. I thought a Orifice bench is ratiometric and a pitot is non-ratiometric

The 2nd email
In a ratiometric bench, the air that passes through
the test piece is about the same temp as when it
passes through the flow measuring device. In this
case, the density of the air is not critical for a
couple reasons.

In a non-ratio metric bench, the air is not the same
temp when it passes through the test piece and then
measuring device. The air density needs to be
determined and compensated, it is much more critical
for non-ratiometric benches.

When blowing hot air through any flow bench for
exhaust testing, you should do your exhaust testing
first, and quickly before the air gets too hot. With
hot air blowing through the bench, you have other
issues to consider besides air density, but air
density is not critical in a ratiometric setup
Since no one got a temp sensor with their Low cost flow bench kit it must be ratiometric
My advice would be to bring the bench up to what you'd normally be at when testing exhaust and calibrate it right there for the exhaust tests.

The differences are not going to be all that great and it doesn't mean squat anyway as long as you're getting repeatable readings.

Another thing you can do is make up a simple test orifice that is small enough to not be affected by the diameter of the test stand bore.

Bring the bench up to normal operating temp. Pop the test orifice right on the stand and grab a reading. Use it as a verification tool when you're in doubt.

I have an orifice I made and tested on a SF110 20 years ago. I use it every time I start on a new head just to verify my bench calibration. It's always within 1 - 2 CFM of what it tested at waaaaaaay back then.

JMO

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Post by RL »

I asked a friend and this is the email, for other peoples information
From what I understand, ratiometric means any flowbench that uses a
volume measuring device such as an orifice or pitot tube. So no matter
what the ambient conditions are, they will affect the port being tested

and the measuring device the same way, so no corrections are needed.
The
"ratio" of flow between the port and measuring device is always the
same
no matter what the temperature, barometric pressure or humidity. ie if
you test a port at sea level with high baro, 40 C and 95% humidity and
then take that same flowbench and head to the top of Mt Everest, low
baro, -40C and say 5% humidity, the flow will measure exactly the same
because you are comparing volume flow rates.

Now with a mass flow device such as a laminar flow element, you need to

measure and correct for baro, temp and humidity each test because the
mass will change with varying weather conditions. Not a ratiometric
design.

A SF600 has no temp gauge because both the orifice and test piece are
on
the same side relative to the motors. So the same air temp is seen by
head and orifice. Inlet testing, both have ambient temp air. Ex
testing,
both see the same heated air from motors. So a true ratiometric design.

A SF110 is somewhat ratiometric because it uses an orifice but having
the motor between the head and orifice means temps will be different so

that's why corrections are necessary. However, no need to correct for
baro or humidity.

Maybe that's why the FP1 has that option, for benches that have the
motor between the test piece and measuring device.
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