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Calibrating Pressure Sensors with SM4

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  • Calibrating Pressure Sensors with SM4

    Hi all,

    Trying to install pressure sensors for a bit of extra safety.
    This is probably very simple for most of you.

    Have a 100psi 0-4.5V bosch sensor for oil pressure, wired to analog 1.
    Have a 150psi 0-4.5V no name sensor for fuel pressure, wired to analog 2.

    Can someone please assist with the calibration, should I be making a table in linear 1?
    I've played with linerise option, span and offset going off research I have done one here but cant get it to be accurate.

    I would also like to have a water pressure sensor, any ideas for an extra input?
    I use HSI's for vvt and rear wheel speed. (FWD turbo)


  • #2
    Are you sure the sensor outputs are 0 - 4.5v? Or could they be 0.5v - 4.5v?

    Are you using the O2 input for normal running? It can be used for another pressure sensor.


    • #3
      For a 100 psi sensor with 0.5 - 4.5v output range the Span value is 580 and Offset is -862.
      For a 150 psi sensor with 0.5 - 4.5v output range the Span value is 387 and Offset is -1292. Select Analog 3 as the input, not Analog 2 (which scales the input differently for SM4 Standalone ECU's).

      For the 100 psi sensor set the channel Minimum allowed value as -0.3 bar and the Maximum allowed value as 7.2 bar.
      For the 150 psi sensor set the channel Minimum allowed value as -0.5 bar and the Maximum allowed value as 10.8 bar.

      What is the engine?


      • #4
        Thanks heaps Ian,
        Got oil pressure to work on analog 1 but analog 2 for fuel was so far out, now I see why.
        Not using O2 and had set that up wiring wise for the water pressure, but wanted to confirm if it was the correct way or not. So thank you again.

        The engine is a 1840cc mazda BP turbo with the late model VVT head, stock cams, 4age quad throttle, e85 fuel making 380KW to the wheels at 2bar.


        • #5
          Doesn't that engine only have a single cam sensor, used for both variable cam position and Sync? So the HSI's would be 1x driven and 2 x non-driven wheels?


          • #6
            My engine has crank sensor and cam sensor, i just use a single rear wheel for speed input for boost boost control.

            The calibration settings worked for sensors thank you lots.

            Going to add the water pressure one, using 02 input, no water pressure preset so just use a "user pressure"?

            And everything is bar, can it convert to psi?


            • #7
              The User pressures display as kpa. If you want the numbers to represent psi you could select the variable as a Feedback pot and do the Span and Offset to represent psi. The unit would display as % but would be psi.


              • #8
                Thanks Ian, easy enough to keep an eye on 150kpa when we are upping the boost over 2bar.


                • #9
                  Hi Ian,

                  Any chance of a breakdown of the formula to get those span and offset results for future? I would like to learn and not have to ask these probably simple questions.


                  • #10
                    The software can do the linear calculations for you. When you are in the channel setup page first select the Destination parameter then go to menu Edit-Window and select Calculate analog span/offset. If the sensor has a 0.5 to 4.5v range and a 5v range, enter the minimum voltage as 0.5, the maximum voltage as 4.5 and the range as 5v. The Span and Offset values can then be calculated.

                    For explanations, the Help shows more details when you highlight the Span or Offset lines in the channel setup screen.
                    However, generally the Span is the number of mv (millivolts) for a 10 bar pressure range and the Offset is the pressure value if the sensor graph was extrapolated to 0v and determined to 2 decimal places, but not inputting the decimal point. The AF ratio Span and Offset works the same way. A Span of 2500 would imply a 2.5v change in signal would change the AF ratio reading by 10 while an Offset of 900 would be an AF ratio of 9.00 if the input signal was 0v.


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