AFM scaling in Nistune, need actual flow data (g/s) for an Z32 AFM

[burn4005]

Hi, I am looking to set up a flow test bench to perform some validation of some fuel system components.

I have some air flow meters sitting here (specifically Z32 AFMs) that i would like to use to meter the air entering the combustion process to validate the fuel flow against that, based on resuting lambda data.

I have found the MAF scaling tables in nistune, that are read in (0.08-5.12v) that scale between 0.07 to 100% of maximum MAF flow. my question is what 100% corresponds to in actual airflow in g/s?

if anyone else has accurate calibration data for any MAF sensors that would be helpful.

thankyou.

[djr81]

The only one I have ever seen is the Nismo afm chart.  Are there MAF tables in Nistune for those you can use to find an equivalent?

[GTSBoy]

I don't think that you will get that information to the level of accuracy that you want.

If it were me, I would create a way to manually calibrate the AFM. That would involve inserting it into a suitable (long) length of 3" tube (assuming 3" is the right size - choose the appropriate size for closest match to the AFM body) and do some manual measurements with a small plain pitot. The way to do that would be to ensure that the pipe upstream of the AFM was at least 15x the diameter of the tube, (so, at least 1200mm long) and drill a small hole to allow pitot insertion at a point >5D upstream the AFM and >10D downstream the inlet end. Probably put a bellmouth on the inlet end too, to give it the best chance of developing a clean velocity profile by the time it gets to the pitot location. Do a 5 or 7 point equal area traverse. If you're really keen, have another hole at right angles to the first to permit a 2nd traverse across the other plane. Convert all differential pressure readings to velocity then average all those values to obtain average velocity. (Also need to measure temperature and static pressure at the measuring location to calculate air density for the velocity calc). Then with the average velocity and the density in hand, simply convert to mass flow rate.

You can do this at a variety of flow rates to compare against the AFM voltage reading. Be aware though that plain pitot measurements are not good below 5 m/s and the measurement error starts to climb as you go below 10 m/s.

You could use some other sort of velocity measuring device. If you have a very small vane anemometer available (say, 15mm diameter head) and you had good calibration data for it (they always read a little low) you could use that to go direct to velocity. Ditto if you know someone with a proper hot wire anemometer, which is the exact same tech as the AFM you're trying to calibrate, conveniently.

If you can't access any probe style velocity measuring tools, you could make an orifice plate (in accordance with the appropriate standard, which I think is BS 1042, or one of the equivalents) and measure the differential pressure across that. The beauty of the orifice technique is that you can make a number of different sized orifices so that you can extend the bottom end of the measuring range (by using smaller orifices).

Any dP measurement will require that you be able to measure dP. The best/easiest way is with a suitable digital manometer, but you can always make an inclined manometer with a plank and some hose and you would be surprised how accurate that can be.

Whatever length of tube you had the AFM in for these manual measurements (both on the inlet side and the outlet, which could be shorter) would be best retained as a permanent part of your test rig, because it will be a part of the calibration of the AFM.

[burn4005]

ok so I've done some more digging and have come accross this nismo plot of the AFM curve. I have interpolated several points that cross the grid neatly and it seems to line up with the nistune calibration curves.

will see how this goes first and build a manometer/oriface plate/pitot etc if needed. it appears that using a stock RB-26 AFM will be better for my needs as it gives much better flow resolution down low.

 

nismo graph of voltage vs flow:

Voltage (v)	% Scale	g/s
0.080	0.073	0.356
0.160	0.073	0.356
0.240	0.073	0.356
0.320	0.073	0.356
0.400	0.073	0.356
0.480	0.073	0.356
0.560	0.111	0.542
0.640	0.159	0.772
0.720	0.218	1.061
0.800	0.290	1.410
0.880	0.377	1.833
0.960	0.487	2.367
1.040	0.618	3.005
1.120	0.777	3.777
1.200	0.974	4.734
1.280	1.196	5.817
1.360	1.445	7.026
1.440	1.723	8.377
1.520	1.982	9.638
1.600	2.373	11.537
1.680	2.753	13.385
1.760	3.182	15.470
1.840	3.658	17.785
1.920	4.179	20.322
2.000	4.747	23.082
2.080	5.362	26.072
2.160	6.055	29.441
2.240	6.833	33.225
2.320	7.671	37.298
2.400	8.582	41.728
2.480	9.572	46.543
2.560	10.634	51.707
2.640	11.765	57.205
2.720	12.978	63.103
2.800	14.269	69.380
2.880	15.628	75.991
2.960	17.073	83.017
3.040	18.601	90.444
3.120	20.217	98.302
3.200	21.930	106.634
3.280	23.737	115.418
3.360	25.669	124.812
3.440	27.681	134.598
3.520	29.770	144.755
3.600	31.972	155.462
3.680	34.275	166.658
3.760	36.698	178.440
3.840	39.240	190.801
3.920	41.920	203.830
4.000	44.746	217.571
4.080	47.710	231.987
4.160	50.820	247.108
4.240	54.066	262.889
4.320	57.447	279.331
4.400	61.001	296.611
4.480	64.704	314.618
4.560	68.548	333.308
4.640	72.547	352.755
4.720	76.704	372.966
4.800	81.025	393.978
4.880	85.512	415.791
4.960	90.167	438.428
5.040	94.995	461.904
5.120	100.000	486.240

 

 

 

Edited March 3, 2020 by burn4005

[sky30]

On 03/03/2020 at 2:53 PM, burn4005 said:

ok so I've done some more digging and have come accross this nismo plot of the AFM curve. I have interpolated several points that cross the grid neatly and it seems to line up with the nistune calibration curves.

will see how this goes first and build a manometer/oriface plate/pitot etc if needed. it appears that using a stock RB-26 AFM will be better for my needs as it gives much better flow resolution down low.

 

nismo graph of voltage vs flow:

Voltage (v)	% Scale	g/s
0.080	0.073	0.356
0.160	0.073	0.356
0.240	0.073	0.356
0.320	0.073	0.356
0.400	0.073	0.356
0.480	0.073	0.356
0.560	0.111	0.542
0.640	0.159	0.772
0.720	0.218	1.061
0.800	0.290	1.410
0.880	0.377	1.833
0.960	0.487	2.367
1.040	0.618	3.005
1.120	0.777	3.777
1.200	0.974	4.734
1.280	1.196	5.817
1.360	1.445	7.026
1.440	1.723	8.377
1.520	1.982	9.638
1.600	2.373	11.537
1.680	2.753	13.385
1.760	3.182	15.470
1.840	3.658	17.785
1.920	4.179	20.322
2.000	4.747	23.082
2.080	5.362	26.072
2.160	6.055	29.441
2.240	6.833	33.225
2.320	7.671	37.298
2.400	8.582	41.728
2.480	9.572	46.543
2.560	10.634	51.707
2.640	11.765	57.205
2.720	12.978	63.103
2.800	14.269	69.380
2.880	15.628	75.991
2.960	17.073	83.017
3.040	18.601	90.444
3.120	20.217	98.302
3.200	21.930	106.634
3.280	23.737	115.418
3.360	25.669	124.812
3.440	27.681	134.598
3.520	29.770	144.755
3.600	31.972	155.462
3.680	34.275	166.658
3.760	36.698	178.440
3.840	39.240	190.801
3.920	41.920	203.830
4.000	44.746	217.571
4.080	47.710	231.987
4.160	50.820	247.108
4.240	54.066	262.889
4.320	57.447	279.331
4.400	61.001	296.611
4.480	64.704	314.618
4.560	68.548	333.308
4.640	72.547	352.755
4.720	76.704	372.966
4.800	81.025	393.978
4.880	85.512	415.791
4.960	90.167	438.428
5.040	94.995	461.904
5.120	100.000	486.240

 

 

 

Message sent mate.