TimZ Posted January 1, 2008 Share Posted January 1, 2008 I totally agree. There are 256 "voltage" steps (0-255) from 0V to full scale on the input of the ADC. The MAP sensor converts pressure to voltage. The circuit in the MS translates the MAP sensor output voltage range to match the ADC input voltage range (or at least it should) to maximize dynamic range. The firmware then uses a lookup table of some sort to convert voltage levels to actual pressure which the interpolation algorithm uses. This is how I think it should work (then I did a little testing). The firmware I'm running (Extra code 029v) appears to limit the max kPA value to 255 no matter which sensor I have selected under "Engine Constants". In my mind this should be a bug as the maximum value you can enter in the VE or spark table in the load band column should equal the max boost your sensor supports. If this is truly the correct behavior, then you would need to think of it as an 8 bit number like TimZ said, and do the scaling in your head. Again, this does not seem right. Why not have the processor do this math for you (unless MS1 with extra code and a 12x12 table does not have the cycles to do this computation in real time). Make sense? I think the reason is most likely that the A/D converter section of the micro uses a single voltage reference for all 8 A/Ds. This dictates that all of the A/Ds have the same 0-5V input voltage span. You can't have it customize the input range of just the MAP sensor channel without screwing up the other seven channels, too. As far as the scaling goes, it makes sense that the MS itself would not do any scaling - it really doesn't need to know what the scale factor is, so long as it's consistent between the input and all of the tables that use it. The scaling should all take place in the calibration and datalogging software so that the users can better understand what they are looking at. Hopefully I'm not coming off sounding like a jerk on this subject - while this might seem like minutia, it's really easy to be fooled into thinking that the processor is doing more for you than it really is, and it's really easy to get "lost" if you are making the wrong assumptions as to what is going on. Quote Link to comment Share on other sites More sharing options...
z-ya Posted January 2, 2008 Share Posted January 2, 2008 I think the reason is most likely that the A/D converter section of the micro uses a single voltage reference for all 8 A/Ds. This dictates that all of the A/Ds have the same 0-5V input voltage span. You can't have it customize the input range of just the MAP sensor channel without screwing up the other seven channels, too. Actually, you can. You just need to make sure that the MAP sensor voltage range matches that of all the ADCs in the processor. Most all processor have a single ADC reference voltage, so you just need to tailor the sensors output voltage range to match that of the ADC. I think for most all people that use the 250kPA sensor, this is fine. When people use higher pressure sensors, and then just start entering kPA numbers in the VE and spark tables, bad things can happen. The table does display kPA as the units, when it isn't. To me, this is broken. Either take the kPA off the VE and spark tables in MT, or fix the firmware to do the conversion. It can be done with a simple lookup table in the firmware. My $0.02. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted January 2, 2008 Share Posted January 2, 2008 This is getting really technical. I like it. I think both Phil and I are running the 4-bar sensor on MS-II. Is the 4-bar upgrade available for older gen MS as well? (Answered my own question, Yes it is.) Quote Link to comment Share on other sites More sharing options...
TimZ Posted January 2, 2008 Share Posted January 2, 2008 Actually, you can. You just need to make sure that the MAP sensor voltage range matches that of all the ADCs in the processor. Most all processor have a single ADC reference voltage, so you just need to tailor the sensors output voltage range to match that of the ADC. It sounds like you are talking about adding (or modifying existing) signal conditioning before the A/D - is that what you mean here? Quote Link to comment Share on other sites More sharing options...
Chemicalblue Posted January 2, 2008 Share Posted January 2, 2008 Hey Phil, I say you just pour some of the 100% meth on the 4 bar sensor and hopefully it will get the hint and start to cooperate. Everyone is making this Soooooooo difficult, just reason with it. Quote Link to comment Share on other sites More sharing options...
TimZ Posted January 2, 2008 Share Posted January 2, 2008 Everyone is making this Soooooooo difficult, just reason with it. Sorry - not trying to be difficult, it's just generally easier to reason with something if you understand how it's supposed to work. Quote Link to comment Share on other sites More sharing options...
z-ya Posted January 2, 2008 Share Posted January 2, 2008 It sounds like you are talking about adding (or modifying existing) signal conditioning before the A/D - is that what you mean here? Not so much making modifications, but just assuming that this is the was it was designed from the start. My point is that the circuit can be designed in a way to maximize dynamic range which will result in full utilization of the 8 bits of resolution. I haven't messed with MSII yet, but does it do the voltage to pressure translation for MAP sensors above 250kPA automatically? Quote Link to comment Share on other sites More sharing options...
big-phil Posted January 4, 2008 Author Share Posted January 4, 2008 thanks guys so much for the replies, I wish I could take credit for knowing what in the hell you guys are talking about. It sounds like I can, if I want to, start my kpa where I want, and end it where I want as long as its in the rang of the sensor it self. Right? That way I can maximize the 8 bit processor and its resolution window? Quote Link to comment Share on other sites More sharing options...
z-ya Posted January 4, 2008 Share Posted January 4, 2008 thanks guys so much for the replies, I wish I could take credit for knowing what in the hell you guys are talking about. It sounds like I can, if I want to, start my kpa where I want, and end it where I want as long as its in the rang of the sensor it self. Right? That way I can maximize the 8 bit processor and its resolution window? You can assume that 255 entered in the load column is equal to your MAP sensor's max pressure. So if you have a 400kPA sensor, and you have told MS about it in the "constants" section in MT, then you might be good to go. The key word is "might". I wouldn't assume anything. I would test the MAP sensor with a compressor and regulator to see where in the 0-255 range your target boost pressure resides. So if you want to run 30psi, set the compressor regulator to 30psi and connect it to the MAP sensor. In MT fill in the load column with equally spaced values from 0 to 255 and see which load band is active. Let's say the active band is 200. Make that the top load band. Make the bottom load band a little lower than idle vacuum. Fill in the rest of the load column per you liking. Hope this makes sense. Quote Link to comment Share on other sites More sharing options...
TimZ Posted January 4, 2008 Share Posted January 4, 2008 I wouldn't assume anything. I would test the MAP sensor with a compressor and regulator to see where in the 0-255 range your target boost pressure resides. Good Advice - that was pretty much the main point I was trying to get across, too. Quote Link to comment Share on other sites More sharing options...
TimZ Posted January 5, 2008 Share Posted January 5, 2008 It sounds like I can, if I want to, start my kpa where I want, and end it where I want as long as its in the rang of the sensor it self. Right? That way I can maximize the 8 bit processor and its resolution window? As far as I can tell, this is correct. Just realize that you are not increasing the resolution of the sensor or the A/D converter. The minimum pressure increment you can resolve with the Sensor - 8bit A/D combo doesn't change and will be 1.6kPa if you are using the sensor mentioned above. What you are doing is getting the most out of the available MAP breakpoints for your application. Pete's suggestion of testing the system by applying known pressures at the sensor is a very good idea. Never hurts to be sure of what you've got. Quote Link to comment Share on other sites More sharing options...
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