MPX5100DP problem with slope

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MPX5100DP problem with slope

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Contributor I

Hi!

I want to measure water level (+/- 2 m) in my tank using a pressure sensor MPX5100DP.

I use the schematic of AN1516 (figure 3) with a (air) pipe in water. The pressure in the air pipe is measured by the positive pressure inlet of the MPX5100DP.

When I try to calibrate the sensor (Vs = 5 V) I get a slope of 3,1 mV/cm water level.

If I read the data sheet, every 1kPa of pressure will give 45 mV Vout. But a pressure variation of 1 kPa is caused by a water height of 10 cm! So I must have a slope of 4,5 mV/cm...

How is it possible?

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NXP TechSupport
NXP TechSupport

Hi,

Please share the equation(s) you use to calculate the slope of water level.

 

Also, make sure you perform the Autozero calibration as stated in application note AN1636: https://www.nxp.com/docs/en/application-note/AN1636.pdf

 

For all NXP standard pressure sensor products, any environment other than dry air, will may have some impact on the reliability and lifetime of the product. NXP's silicon pressure sensors are NOT compatible with oil, gas, petrol and can be affected by water or water vapors, or other chemicals.

A determination must be made if this impact is acceptable for the application.
Possible solutions to use our sensors in applications with other media than dry air:
Besides the mechanical stresses to the inside of the package, there would also be a need to evaluate stresses the hardening/ed material induce on the outside of the package. To minimize these, a low stress encapsulant should be used. And, of course, any recalibration/autozeroing of the device after a point of potential stress induction would be highly recommended and could alleviate any mechanical stress concerns if done before a measurement (and the temp delta's are minimal during the readings).
In the application note AN3728 is discussed the media compatibility for the NXP Pressure Sensors. In this application at page# 3, you can see that we have tested a couple of media and using the Air column method (Figure 2 of this document) to measure water level is unlikely to have issues, but we cannot give a guarantee about the long term reliability of these devices under these conditions.

AN3728: https://www.nxp.com/docs/en/application-note/AN3728.pdf


Have a great day,
Jose

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