PTS Flowbench Forum

As some of you already know, I fabricated my own flow bench based upon a Nissan 300ZX Twin Turbo MAF Sensor to measure airflow.
There are 4 wires for the MAF Sensor; Pos / Neg 12VDC power, and Pos / Neg Signal Voltage (0.5VDC to 5.12 VDC) which is monitored with a Fluke Digital Multimeter. Power is supplied by a 12V Gel Cel Hobby Starter Battery (From Hanger 9).
The MAF Sensor is mounted directly below the Bore adapter. Mounted to the Exit of the MAF is the Manometer connection, and the Vacuum Source Manifold.
The Vacuum Source is 8 Lamb Vacuum Motors, 4 mounted in parallel, and 4 mounted in series.
Each of the Lamb motors are 2 stage. All of the exit air from the first motor, is supplied to the inlet of the motor in series, essentially making 4 stages.
With all of the motors running flat out, and no head installed, the the Manometer showed 36" WC, and obtained 4.68V reading (Which equals 611 CFM).
After a test piece is installed, the test procedure is as follows:
1. Disconnect the battery charger and Record battery voltage.
2. Connect Multimeter leads to Sensor wires
3. Turn on power switch
4. verify 0.5 VDC or less reading on Multimeter
5. Open test piece valve to first increment.
6. Turn on power for vacuum motors and adjust motor speed to obtain 28" WC (sum of upper & lower fluid levels)
7. Record voltage reading
8. Open test piece valve to next increment.
9. Adjust motor speed to maintain 28" WC.
10. Record voltage reading.
11. Repeat Steps 8-10 til maximum valve opening.
12. Shut down power to motors and MAF.
13. In Excel, Convert MAF readings to CFM and record.
14. Create Flow Charts in Excel.


As you can see, it's a fairly involved process, which I would very much like to streamline.
Installing a PTS Digital Manometer would be the first step, but how can I "Hook-Up" my computer to control, convert the voltage readings and record the CFMs?
The goal is to set the WC setting and have the computer control the motor speed.
Eventually I'd like to have the computer control the test piece valve opening as well.
Is there anything off-the-shelf that could adapt to my application?

1. Disconnect the battery charger and Record battery voltage.

Replace this combination with simple 12vdc power supply for suited current draw, i would also use in parallel a large filter capacitor for both voltage surge stabilization and any noise in the line. This MAF can't be drawing to much current.

6. Turn on power for vacuum motors and adjust motor speed to obtain 28"

PM Bruce about the Parts list for the SCR motor speed controller configuration used on the PTS/FBT benches.

9. Adjust motor speed to maintain 28" WC.

Bruce sells a Motor speed controller that uses PID technology it works with the above SCR setup.

10. Record voltage reading.
13. In Excel, Convert MAF readings to CFM and record.
14. Create Flow Charts in Excel.

I am making some assumptions that you have the necessary programming skills to perform these items along with at least the basic knowledge of VB Script or Visual Basic, the Dataq products will do everything you would like except make the system closed loop.

Now if you are skilled and want to do all the above the item best suited is the Arduino Uno http://arduino.cc/en/Main/ArduinoBoardUno This little wonder can do your A to D for your voltage it dose PWM to feed the SCR for motor control and can also do stepper motor controlling for your auto valve opening. If you have programming skills in one of many sets this little board has what you need, it does 10 bit AD so your sensitivity would be about .0048 VDC (Not sure how that works out to cfm sensitivity) but it is all here in one board with minimal electronics needed.

Rick

1960FL wrote:
Replace this combination with simple 12vdc power supply for suited current draw, i would also use in parallel a large filter capacitor for both voltage surge stabilization and any noise in the line. This MAF can't be drawing to much current.

The Nissan MAF is a hot wire device with an internal five volt regulator, so the incoming dc supply voltage and supply noise should not present a problem when run from a 12v battery.

What may (?) be a much bigger problem is air turbulence entering the MAF.
Air velocity is only sensed in one very small location over the whole flow cross section, and any flow bias, swirl or turbulence will create non repeatable results.
An up stream drinking straw air straightener may be a step in the right direction with that.

The output characteristic of the Nissan MAF, is a fairly radical curve of constantly changing slope. It is going to be very difficult to convert MAF output voltage to flow numbers with any real accuracy.
About the only way to do it might be a multi order polynomial correction in software, pretty tricky stuff and not for the faint hearted.

I tried to do something like this myself with a Nissan MAF many many years ago, and the problems are formidable.
It is definitely not the very simple way to measure airflow it may at first appear to be.

Hmmm, all I can say is that I've had VERY repeatable results with the testing I've accomplished with this set-up.
When doing Baseline Testing, the voltage readings from one port are predictable to the next same style port (LH to LH, and RH to RH).
I use the following equation (in excel) to determine CFM:
CFM=(A2-0.5)*(675/(5.12-0.5))
where:
A2 is the recorded signal voltage reading
MAF Voltage range is 0.5 to 5.12
675 is the maximum CFM rating of the MAF

During baseline testing of a customer L-28 (280Z) head the voltage readings between like ports and valve opening settings were identical or almost identical.

The same can be said for the H-D Twin Cam and SBC heads I've done as well.
The L-28 head is a high swirl design, where the SBC & H-D heads are not.

on a sidenote:
During testing of the L-28, a small ball of modeling clay got sucked into the bore adapter.
It was whirling around inside the bore adapter like crazy!
Just to see if what effect the valve placement had on the swirling motion, I put an "Airsoft" pellet in and sure enough, the ball would spin
one direction for the LH port and spin the opposite direction for the RH port.

My bench set-up is typical with a head adapter, and bore simulator (both bore and stroke) all of which I leak test and ensure are sealed before any testing commences. The MAF is mounted directly below the Bore adapter.

http://i1134.photobucket.com/albums/m61 ... G_0207.jpg

Photo of the Vacuum Motor Set-up (4 in Parallel and 4 in Series):
http://i1134.photobucket.com/albums/m61 ... G_0204.jpg

Rest assured I wouldn't have gone down this road if my results were unpredictable and non-repeatable.

S2Z wrote: I use the following equation (in excel) to determine CFM:
CFM=(A2-0.5)*(675/(5.12-0.5))

That formula assumes that the MAF output voltage rises in a straight line linear relationship with CFM.

I can assure you that the output voltage is anything but linear.
Here is a fairly typical MAF output voltage curve I found on the internet. I have absolutely no idea what it is for, but the shape would be very typical for any MAF



The gross non linearity is not a problem, in fact it could be a definite advantage to have much higher flow resolution down at very low flow values.

The difficulty is, that the MAF voltages don't actually mean anything in regards to flow figures unless you can find a flow curve for your particular MAF.
So you cannot compare what you are "measuring" to anything else or really know where you are.

It is probably a very sensitive tool for comparative measurement for back to back tests.

But at (say) at half valve lift, you are reading perhaps 3.4 volts of MAF output, is that a good air flow figure ?
Is 3.4 volts 15 CFM or is it 150 CFM of airflow, or something very different ??
There is really no way to tell.

So as to better clarify what Tony is saying this is the same graph with a linear graph added for comparison, you can see what the drastic difference is at a given voltage mid range. Do you have any part numbers and model year for the unit you are using?

Check this link they may have a good table to start a ampping from.

http://www.microsquirt.info/mafmap.htm

Rick

Rick,

Great minds think alike
Way back in the dim distant past I tried to use one of these same Nissan hot wire flow meters as a flow bench measuring element with a leaf blower.
I still have it, and here it is:



This one is known as a "Z32 type" a Nissan designation, and the orange sticker has written on it:
22680 30P00 A36-000 N62
Unisa JECS CORPORATION made in Japan

I tried very hard to get information, and particularly a flow curve for it, but nothing seems to exist in the public domain.

I did pull it to bits and try to reverse engineer the circuit board, but being surface mount with all blank unmarked components, that proved to be impossible.
It is all analog with an internal five volt regulator, but how it actually works is still a complete mystery, and I could never find any information on it.

Nissan use a range of flow meters in different vehicles, and they all seem to use a very similar if not identical hot wire sensor circuit board placed in different diameter flow tubes for different flow ranges.
I eventually gave up on this idea and started looking at vacuum cleaner motors and orifice plates.
It was all a very long time ago........

Tony,

It might be fun to flow one now that i have a DM, you could use one of those slide valves and just start at closed and increment it open say use a 1/4 - 20 threaded rod and go 1/4 turn per recording and build a mapping table in which your software could do lookups. I do understand the one benefit of this design as you would not have power loss associated with Delta P and thus in low power applications you might have an advantage but then again i would go to a Pito Tube as there is simple math to make digital and my guess is that before long the FlowSoft will support the Pito Tube.

Hope you are doing well this Holiday season and enjoying the Warm weather....

Rick

That is a very interesting idea Rick.

These particular hot wire MAFs have the potential for excellent low flow resolution, and the flow tube diameter can readily be changed to suit any desired flow range with absolute minimal pressure drop.

If the "funny" flow curve problem could be overcome with a lookup table, as I am sure it could, it would be huge step in the right direction.
I had actually seriously considered doing that with a microcontroller, but at the time I had no means of actually establishing what the real flow actually was.

Chicken and egg situation.
I needed a flow bench to build a flow bench, so it never happened.
Just one of may ideas that never went any further.

Tony

Noby said our flowbench was the best it just works and works well, but if we could help other find there dream then Why not..... I have to say with the Dataq product and some simple VB or even VB Script it could be done. If you were all on your own it could be done with Orifice plates and then extrapolate the curve between points. My thoughts were live motor sampling, i am looking for something i could adapt to the carb intake and make passes at the track and use the data for tuning and R&D.

Rick