Calibration of Simulated Manifold Pressure Sensor (MPS)

I previously wrote about how to simulate an MPS in KiCAD. Here is how to tweak the model to match your specific MPS.

1. Apply zero to 15 inHg to the MPS and measure the primary (pins 7 – 15) and secondary (pins 8 – 10) coil inductance for each. For the purposes of this post primary is called L2 and secondary is called L1 (yes, backwards I know).

2, Update the following lines in the model to insert your values. 351m = 351mH. Leave the ‘1e308’ in there.

* Primary coil inductance look up table by vacuum, in Henry
.func LpriTable() { vac == 0 ? 375m : vac == 1 ? 375m : vac == 2 ? 358m : vac == 3 ? 350m
+ : vac == 4 ? 342m : vac == 5 ? 335m : vac == 6 ? 327m : vac == 7 ? 320m : vac == 8 ? 313m
+ : vac == 9 ? 306m : vac == 10 ? 300m : vac == 11 ? 292m : vac == 12 ? 286m
+ : vac == 13 ? 279m : vac == 14 ? 271m : vac == 15 ? 265m : 1e308; }

* Secondary coil inductance look up table by vacuum, in Henry
.func LsecTable() { vac == 0 ? 731m : vac == 1 ? 731m : vac == 2 ? 703m : vac == 3 ? 689m
+ : vac == 4 ? 678m : vac == 5 ? 665m : vac == 6 ? 654m : vac == 7 ? 641m : vac == 8 ? 629m
+ : vac == 9 ? 618m : vac == 10 ? 607m : vac == 11 ? 596m : vac == 12 ? 584m
+ : vac == 13 ? 572m : vac == 14 ? 560m : vac == 15 ? 550m : 1e308; }

3. Connect pins 7 and 15 together, shorting that coil.

4. Apply zero to 15 inHg to the MPS and measure the secondary (pins 8 – 10) coil inductance for each. This measurement is called Ls.

5. Put the L1, L2 and Ls values into a spreadsheet using Henrys for the units.

6. For each vacuum level calculate the coupling factor using the Excel formula:

=SQRT(1-(Ls/L1))

replacing Ls and L1 with the corresponding cell references. Look at this screenshot for an example:

7. Insert the coupling factors into this line of the model:

* Coupling factor look up table by vacuum
.func kTable() { vac == 0 ? 0.940646225 : vac == 1 ? 0.940646225 : vac == 2 ? 0.937901171 : vac == 3 ? 0.93644171
+ : vac == 4 ? 0.935217231 : vac == 5 ? 0.933744986 : vac == 6 ? 0.932426383 : vac == 7 ? 0.930837611 : vac == 8 ? 0.929297049
+ : vac == 9 ? 0.927815404 : vac == 10 ? 0.926277558 : vac == 11 ? 0.924680246 : vac == 12 ? 0.922882619
+ : vac == 13 ? 0.921005835 : vac == 14 ? 0.918947379 : vac == 15 ? 0.917110086 : 1; }

8. Measure the primary (pins 7 – 15) and secondary (pins 8 – 10) coil resistances in Ohms. Put those values into these lines in the model

* Resistances of primary and secondary coils, in Ohms
.param Rpri=92.5
.param Rsec=348

And done! Enjoy!