Datalogging Motorola MPX4250

[thommo]

Hey guys first post here

Just have a quick question about the Motorola Map sensor that i got from feescale.
I need to fill in the lookup tables for the sensor.
After reading the datasheet im still a little confused.
I think it is saying that 0v = 0kPa and 5v = 250kPa.

In the AUX1.csv i have 0v = 0psi and 5v = 36.259psi.

Is this correct. I am yet to test this as i wired the dlp converter wrong and fried it so i have to wait for another to be delivered.

Attached is datasheet for reference

Any help will be greatly appreciated

Thanks
Scott

[Matt]

Looks fine to me. I've got to test mine out this week

[thommo]

Thanks Matt ill give it a go when i get the DLP. Ill let you know if i have any problems

[Matt]

All running fine in the 0.10 versions with this sensor. Works a treat

[ttcarguy]

S/W : Windows XP, NIStune : 0.10.11
H/W : Type 2 Board, DLP-IO8-DS, MPX4250 and AEM UEGO Wideband.

I am trying to display and log air pressure using a DLP-IO8-DS, MPX4250 pressure sensor and NIStune.

Note: although I have an AEM Wideband, it is not connected for the tests below. When it is connected it does not use the DLP, I use a separate USB-to-serial interface.

At this point 0 psi is being displayed as 9.00 in the Wideband window under Air Fuel Ratio and I don’t know what I am doing wrong (I assume 0 psi should display 0 in the Wideband window)

In NIStune, via configuration, I configured the Wideband Type as DLP A/D converter and entered the port the DLP is on. I modified the afr1.csv file in the Wideband\DLPADConverter directory (0000,0 and 5000,36.259). When I click on the ‘WB O2 LH’ button in NIStune, it connects and the Wideband window is displayed. The value that is displayed is 9.00. Aux1-Aux6 are 0.00. The value should be 0.00. When pressure is applied the MPX4250 the Air Fuel Ratio value does respond and increases…but I believe it is incorrect by at least 9 psi.

I am able to connect to the H/W via HyperTerminal. The output voltage is .20 volts when there is no pressure and the voltage rises as air pressure is increased. So I am assuming there is no problem with the DLP and MPX4250.

I have the same issue with NIStune 0.9.14.22.

Not sure this is related to the post viewtopic.php?f=18&t=1969

Help!

[ttcarguy]

I tried moving the output signal for the MPX4250 from channel 1 to channel 2 of the DLP. I grounded channel 1 via DLP GND. I updated aux1.csv and NIStune now displays the correct value in AUX1: 1.48 ~ .20 volts. The AFR still displays 9.

At this point I am not sure why the MPX4250 has an output voltage of .20 volts as opposed to 0. Any ideas?

[Matt]

On the DLP the first input (1) is tied to the AFR (LHS), so use input (2) for AUX1, 3 for Aux2 and so on

[ttcarguy]

Thanks for the reply Matt.

Reading the data sheet for the MPX4250 and it specifies the voltage range is .20 - 4.9 volts (0-36.3 psi). So my reading of .20 volts at 0 psi is normal.

Not sure why people are using 0000,0 and 5000,36.259 in the csv? 0200,0 and 4900,36.259 are more accurate.

I did not use 36.3 since this is a rounded value for 36.259psi = 250 kPa which is what the MPX4250 specs say is the max pressure.

Doesn't make a huge difference (~1.5 psi), but large enough that you would want to correct for it in the csv.

[tastyratz]

actually, to be even more accurate... reading from 0 psi as a start would not be correct. the sensor starts at 0 kpa which is -14.5037738 psi. Wouldn't it be more accurate to start at 200,-14.504 and finish at 4900,36.259? 0 psi atmospheric is after all, 100 kpa...

[PL]

I guess it depends if you want 0psi boost to read 0psi or proper atmospheric pressure of 14.5psi.

Personally I like 0psi boost to read 0psi.

I used my DLPIO with the MPX4250 last week and it worked a treat. Very happy. I used 0200,0 and 4900,36.259 and it appears to be spot on.

PL

[tastyratz]

I do prefer 0psi to read 0psi, I was under the impression that it would erroneously report by reading the white paper. I have purchased one but not yet used it.

Although I suppose it also matters if you purchased the absolute sensor vs the regular one? I was thinking the sensor ranging down to 0kpa...

[PL]

Yeah, depends which sensor you get. But those values work just fine for the "gauge" ported MPX4250 (MPX4250GP).

You could also use the Differential version - this would allow you to directly measure pressure drop across intercooler cores by connecting a hose before and after IC.

PL