barometric correction

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AndreyB
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barometric correction

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this a thread to discuss what would need to be done under the umbrella of https://sourceforge.net/p/rusefi/tickets/194/ "barometric correction" feature

I would need to re-read the amazing link @ has provided, but so far it looks like the sub-tasks are

#1.0: support for separate Baro sensor (is it really needed?)
#1.1; initial MAP reading would be initial Baro value
#1.2: a set of criteria defining 'pseudo Baro read' approach (seems like a number of TPS and RPM sets with thresholds? todo: figure this out)

#2.0: Baro part of speed density calculation: an curve of 16 elements (4? 8?) for VE_mult(Baro) multiplier for http://rusefi.com/wiki/index.php?title=Manual:Software:Fuel_Control#Speed_Density

Did I get at least part of all this right?
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Re: barometric correction

Post by puff »

a separate baro is very much needed in case you live in the mountains, when the altitude changes significantly within one trip.
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Re: barometric correction

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Agreed, baro sensor should be added to Frankenso. I just added it to the known issues list. Should we use an analog one, or a digital one? I know there has been discussion about this one http://datasheet.octopart.com/BMP085-Bosch-datasheet-32780306.pdf which uses I2C for communications. However what happens if you have this in your cabin, it might not match the real baro reading. I tend to think the baro should have the ability to have a hose connected such that the sensors sense point can be moved. Perhaps something like this guy https://octopart.com/mpx4115as-freescale+semiconductor-800701

Also how do you mount it such that you get a real baro reading. I tend to think you don't really care about Baro, but what the intake pressure at the air filter is. AKA if you are moving fast up Pikes Peak, the air being smashed into the front bumper will increase the air pressure from what it would be when you are not moving. your VE will really be based on how much air is available at the intake, which will vary based on baro, but I tend to think you really care how much pressure you have at the intake.

Also about the thirdgen forum post, I agree VE will change based on baro as well it will change based on temperature, humidity and %O2 in the air. But I don't agree with the math. He posted this equation(VE% * Mbaro) / VEbaro = VEreal% Where Mbaro is the measured baro pressure and VEbaro is the baro pressure from when you tuned your VE table. However lets go to the extreme with a baro of 0kPa which is found in space vacuum. That equation claims at 45kPA you'll have 100% VE, and you'll be above 100% VE when below 55kPa. So the natural process would be to run your engine in space as you'll get more HP.
thirdgen_VE.PNG
I suspect this equation is a ballpark that is probably better than no corrections, but I feel it has some fundamental flaws. I'd like to find a more detailed and better version of that equation. Perhaps something that notes some of the backing math and science.

I understand this typically only applies to MAP and does not apply to MAF.
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Re: barometric correction

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Because we are starting to consider more accurate O2 predictions, I'd like to suggest we also start to consider humidity. I'll probably add the HIH6120 to the R0.4 board. I have added this to the known issues list, which will remind me to add it when I find time.

84) add humidity sensor perhaps HIH6120-021-001 or DHT11

Here's some link about these devices.
http://www.adafruit.com/products/386
https://octopart.com/hih6120-021-001-honeywell-55424641

The HIH6120 costs more, but covers a wider range. As well you can get it from a source that is not some random Chinese supplier.
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Re: barometric correction

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Re: barometric correction

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Image
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Re: barometric correction

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Looks like this one is good http://www.findchips.com/search/BMP183 It's under $5 and breakout boards from AdaFruit can be obtained. I think I'm going to add this to Frankenso R0.4. Does anyone have any suggestions? I'm thinking we should use a digital one as we are getting low on analog IO. I would kind of like a Baro with a barb that allows for the baro reading to be remote located. However so far all the digital ones with a barb that I've found have been $20+.
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Re: barometric correction

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What is the advantage of SPI over I2C?
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Re: barometric correction

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kb1gtt wrote:I think I'm going to add this to Frankenso R0.4
Does not it look like OEM manage to read baro from the MAP sensor uder certain load? I do not think that baro is such a pressing issue that we would need to add a dedicated sensor.

I guess eventually we would want waterproof case and would not we have to use external sensor in this case? My preference is with external baro sensor or using MAP for Baro, not baro on board.
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Re: barometric correction

Post by kb1gtt »

We already have SPI, I2C would be an additional dev cycle, but could be do-able if a sensor is found. I see this as one IO for SPI's enable line, while I2C would require 2 IO. Perhaps the Analog isn't so bad. We technically only use 5 of the 12. However I also know they are limited resources so I tend to think we should avoid using them, as we'll surely want them for something as soon as they are missing. I know the truck has several items like fuel level and battery temperature which are analog signals.
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