Calibration Help

[r2dudes]

First off I would like to thank Bruce you are truly a special person, thank you for making my dream of owning a working flowbench a reality! Secondly to all of you members for the amazing information and discussion that all of you have provided for me. Now to my question I just got my PTS bench built and running I have 4 of Bruces plates along with a DM . Do I have to change the orifice diameter in Flowsoft to match the plate that I have in the box? Is there anything else I need to change to calibrate to a known plate ??

Again thanks

[Brucepts]

Calibration instructions are posted in the PTS Flowsoft area of the forum, should find what you are looking for in there.

[1960FL]

Dudes,

Here goes,

First the plates that you use inside the box are installed based on the direction of flow sharp edge (None beveled side) against the air flow I/E while the bench is in "Intake Mode" the sharp (None beveled) edge is up. Second the DM uses a 16" Delta P so the calculations for flow of the orifice will be based on this not the 28" used for test pressure. If you got 4 plates from Bruce my guess is that you got a 100 & 200 & 300 CFM at 28" calibration plates and a 660cfm at 16" internal plate or something like that. Bruce may have also given you the math for the other plates at 16"

Now that you may be confused you will install the biggest plate you got from Bruce with the 16" flow rating on it inside the bench. You will start FlowSoft and open the configurations, set the orifice diameter to the ID that Bruce gave you say 660 @ 16 or 3.490 so you would enter the 3.490 in the orifice setting in FlowSoft. Then go to the Discharge Coefficient and set this to .600 to start. You will need to make sure all your other settings are correct (Normally they are with the setup Bruce pointed you to. Make sure your comm port setting are right and close the configuration.

Start FlowSoft and make sure your numbers begin to show, if they wonder a little at first do not worry about it we are just checking the setup. Place the 100cfm plate on the flowbench sharp edge up (assuming intake mode) Turn up the motors a little and see if you are plumbed right and you should get Depression and flew readings. Turn all the motors off and click the check box on the FlowSoft main screen that says "Show Values" in the box to the right with the heading of Avg. Observe the values of channel 1 and channel 2 write these numbers down. Now click the stop button on FlowSoft and go back to your configuration page. In the channel 1 & 2 offset settings enter the numbers you wrote down rounded to the next highest number, close FlowSoft and click the start button again the Depression and CFM numbers should be at 0 if not adjust the offset until you are stable at .01 t0 .00.

Now with the 100 CFM plate on top of the bench if not bolted down run a quick lick of masking tape around all 4 sides of the plate to ensure proper seal. Slowly runt he bench up to 28" of depression and observe the CFM reading. Remember +/- 2 cfm on the 100 plate is ok to start at, right this number down, now repeat this same test with the 200 & 300 CFM plates on top of the bench. What you are shooting for is a calibration where the 200 CFM plate is close to dead on and the 100 & 300 are +/1 1% or so I/E 100 plate reads 101 and 200 reads 199.9 and 300 reads 296 this would be almost a spot on calibration. you can begin moving the numbers by adjusting the discharge coefficient, remember the the larger the CD the CFM numbers move up the smaller they move down.

Now each time you change the CD you need to re run the test on all three plates, i recommend you you make up a spreadsheet to keep track of the CD and its related flow numbers on each plate otherwise you will end up chasing your tail. Now if the numbers move to fast you will need to adjust your sample rate and averaging in the calibration and learning stage i suggest a sample rate of no more than 100 and set your averaging at like 100 to 150. If you get the spread between the two to HIGH ( I/E samples at 25 and averaging at 200) you will be able to watch the number count down after the air flow has been turned off.

This should give you a good start post your questions and results.

Rick

Bruce posted while I was typing LOL....

[coulterracn]

Use the procedure Rick described for both intake and exhaust because the CD value will be different for exhaust mode

Ray

[r2dudes]

Ok I played with this somemore tonight, I have it set perfect on the 100 and 200 plates @ 16 and 28 by changing the CH 2 from .000495 to.000546 The DC is still set at .585 I havent touched it. I have 6 motors in it seems to top out @ 230 CFM @28
I guess my next question is how do I know the depression on channel 1 [ .001085 ] is set correctly? Is this set from Bruce with the DM? I knew I wasnt going to be testing 600CFM at 28 inches I thought 6 motors would get me closer to 400? I have checked for leaks and everything seems good.
I wasnt able to open the DOCX file is there where the calibration instructions are ? I will try on a different PC

Thanks again for the quick responses

Brad

[Brucepts]

Do not change the channel calibration number!

That sets the scale linearity, the only thing you change is the "discharge coefficient" for calibration.

[1960FL]

Dudes,

I have it set perfect on the 100 and 200 plates @ 16 and 28 by changing the CH 2 from .000495 to.000546

Never touch the "Calibration" settings as Bruce said this dictates the scales length this setting should only be changed by the direct discussion with Bruce if he has made a change to your DM and one of it's sensors......

Lets take a big step backwards, What plate is in the the bench ? Give us the numbers off of Bruce's plates he sent you and the one inside the bench.

Now you need to download Rocco's spreadsheet and learn it, understand the math against the plates you have from Bruce. http://www.flowbenchtech.com/forum/view ... ?f=14&t=73

Open this sheet, in the upper section set the orifice diameter to your internal plate size I/E 3.490 set your pressure differential to 16 the sheet should read in this example 660.6 cfm this wold be the maximum amount of air that could flow through your bench.

Remember the 16" number is the maximum amount of pressure differential allowed across the internal orifice plate this has nothing to do with the 28" test pressure so do not be confused. If you do not understand what i am saying here STOP and ask so we can clarify it as this basic principle is how the flowbench works and if you do not get it, it will be much harder on you not only working the bench but understanding what the bench is telling you about the heads you are testing.....

Rick

[r2dudes]

RIck I'm not sure I understand it all could you go into greater detail ?

Thanks Brad

[1960FL]

Brad,

In response to your PM I will get a little long winded here but I hope this helps.

First off if you look at the airflow schematic under flowbench 101 you will see the path of the air from test part through the flowbench intake/exhaust. Form here out lets just assume I am talking about using the bench in intake mode so the air is coming in through the test part and exiting out the bench. In reality I view it more like this, the motors are potential air flow and thus create a vacuum on multiple chambers from the motor inlet all the way up to the upper settling chamber and test fixture/part.

The big difference here is in a sealed bench “No air flow” the entire internals of the bench will fall to a given vacuum “Depression”, but once we begin to flow air through the bench everything changes. In our bench design right smack in the middle we install a restriction between the lower settling chamber and upper settling chamber we call this the internal orifice. Now when we have our test part on top of the bench and start our motors, they begin to pull vacuum this vacuum “depression” builds in the lower chamber first then begins to pull air through our orifice and creates a depression in the upper settling chamber then the air hits its next restriction the test part and air begins to flow through the part. As we turn up the air each of these separate restrictions build greater depressions in the lower and then upper chambers, our test depression is measured (PTS DM Channel 1) in the upper chamber this is the 28” number we speak of. Remember it is not a defacto standard just one our industry chose and a starting point. Some people will test at 10” or 40” or 60” depending on there bench and equipment. The base PTS monometer will allow you to test up to 35” of depression, but I digress.

So here is where the 16” and 28 come together, as we now see the 28” is the test pressure we use as our datum for each test so we can look at the results on a level playing field. But think about this, to get the upper chamber to 28” with the internal orifice plate (restriction) in the middle of the flow the lower settling chamber must work harder thus pull more depression keeping the air flowing. The PTS DM channel 2 measures the difference in pressure between the upper chamber and lower chamber, this we call differential pressure or often we refer to it as Delta P “DP”. The PTS DM is setup to measure a MAXIMUM Delta P of 16” thus if we use Ed’s (86rocco) spreadsheet and enter the number in for orifice diameter and Differential Pressure we can correlate this to the flow number on the plate. Example as above, Bruce shipped me plates for my bench as follows a 100 @ 28, a 200 @ 28, a 300 @ 28 and 660 @ 16 the plates marked as CFM @ 28 are meant to be used as calibration plates on top of the bench, the 16” plate is meant to go inside the bench as our internal orifice (that second restriction). All this is saying is if you could pull hard enough on the lower chamber with your motors to get to a Delta P of 16” the cfm reading would be close to 660 CFM for my plate.

Now on the forum you may here us talk about a Motors ability to flow air at 44” that is because we are assuming one is testing at 28” and is using a 16” Delta P. In my above example if with my test part on the bench my depression set to 28” and I am reading 660 CFM by the math I know the lower chamber is pulling on the orifice plate at 44” 44-28=16. In this case the PTS DM would be seeing 16” of pressure on channel 2 the difference between the two chambers. Bernoulli’s math in FlowSoft converts this differential pressure to CFM based on the other information provided in the configuration settings, like CD and air density etc.

Last if you use Ed’s sheet to play with and if you know the orifice diameter and CD of the orifice you can see what it will flow at different depressions. For example your 100 @ 28 plate should be around 1.18” +/- ID with a .62 CD that same plate should flow 59.8 CFM at a depression of 10”. This is all good to know as it can be used to fine tune your calibration flow your 100 plate at 10” then at 28” check the math etc. You get the picture.

In closing you will find you will need to understand this math over time it will correlate from calibration to Port efficiency understanding that port CSA is almost like the orifice diameter, you are close, work on the calibration and then start experimenting.

Rick

[xe5800]

Thanks Rick,

I know this is an old post but this is a really good example of what actually going on inside a flow bench.

I think I have read it before but now I have pts dm on my sf300 and larrys software for it, this explanation
makes so much more sense now that I can picture whats happening inside the chambers and also the digital mano.

So thanks again mate,

Troy.