Engine cooling pressure

[bbtapb]

Hi.
I'd like to add a cowl differential pressure (top vs bottom) sensor. Lycoming says I should have about 6" water difference. Would this sensor do the trick? And, if it's not too much to ask, an SFG file entry? Thx.
http://www.digikey.com/product-detail/en/freescale-semiconductor-nxp/MPX5010DP/MPX5010DP-ND/464054

 

[kurtfly]

Bob,

This looks like it will work. It outputs ~0 to 5V, but it requires 5 volt excitation. So you will have to get that from some place. Needs to be mounted, designed for a Printed Circuit Board. Calibration is no problem.

If your not planning on installing this permanently then there are easier alternates. An airspeed indicator is a differential pressure gauge. Pitot to the high side, static to the low side. Just need to convert airspeed to PSI or Inches of water.

 

[kurtfly]

Bob,

For the MPX sensor you provided the calibration is y = 0.112119x + 0.200000 to give EU's output in "Inches or Water".

So create a new sensor definition like:


sensor={
id=MPX DIFF PRESSURE
;UN-VERIFIED
function=PRESSURE
pins=C37_P8 C37_P22 C37_P23 C37_P31
name=DIFF PR
min_val=0
max_val=40
resolution=0
round=.1
is_piecewise=0
low_coeff={
c_x4=0
c_x3=0
c_x2=0
c_x1=.112119
c_x0=-.20
}
low_resistance=NONE
low2high_cross=0
high_coeff={
c_x4=0
c_x3=0
c_x2=0
c_x1=0
c_x0=0
}
high_resistance=NONE
high2low_cross=0
window=.2
shift=3
age=16
}

 

[bbtapb]

Thanks!!

 

[kurtfly]

Bob,

Sorry I had an error in my calibration calculation.
Should be y = 8.919080x - 1.783816

sensor={
id=MPX DIFF PRESSURE
;UN-VERIFIED
function=PRESSURE
pins=C37_P8 C37_P22 C37_P23 C37_P31
name=DIFF PR
min_val=0
max_val=40
resolution=0
round=.1
is_piecewise=0
low_coeff={
c_x4=0
c_x3=0
c_x2=0
c_x1=8.919080
c_x0=-1.783816
}
low_resistance=NONE
low2high_cross=0
high_coeff={
c_x4=0
c_x3=0
c_x2=0
c_x1=0
c_x0=0
}
high_resistance=NONE
high2low_cross=0
window=.2
shift=3
age=16
}

 

[bbtapb]

Thanks!
Found this even more convenient.
https://www.widgeneering.com/mpx5010dp_freescale_pressure_sensor_with_carrier.html
This over an ASI because I want it in the data log.

 

[dougnlina]

So I am using this sensor and trying to set it up for inches of water to be displayed on the EMS. I have used the formula as shown in Reply 4 but am getting readings that are not accurate (as compared to an actual water manometer) When I work the equation (limited skills using Excel) I get Kurts coefficients from Reply #2. I have not tried these numbers, but Kurt, I am wondering what "mistake" you found to change the coefficients? I'll report back if the original formula matches the manometer...

 

[kurtfly]

From the vendor data sheet provided in original post we have:

Pressure Range of  0 to 1019.78 mm H2O, convert this to Inches.

mm to Inches is 1 Millimeter = 0.03937007874 Inches.

So, the new pressure range is 0 to 40.14881889 in H2O.

The sensor has a full scale output of .20V to 4.7V (4.7-.2=4.5).  So the slope, C_x1 is 40.14881889/4.5 = 8.92195975.  This is 8.92195975 inch H2O per Volt.

The offset, C_x0 is the sensor offset.  The datasheet shows a typical .20Vdc offset at 0 inch H2O.  This make the c_x0 term (.20 *8.92195975) = 1.784391.  This needs to be subtracted so it makes it -1.784391.

I do not have the original math I used, but I believe I used sensor 1.45 PSID as the starting point and converted to In H2O from that.  Rounding errors.

With 0 pressure applied to both ports, the display on SV should be reading 0.  You can connect a tube between the two ports to ensure no difference.  If it does not you can add/subtract from the C_x0 term to force it to read 0.  this is due to the sensor Minimum Pressure Offset of 0V to .425V, typical is .20V.

I have attached a simple excel spreadsheet that performs the math if you prefer.