Line Pressure reading unstable at zero psi
Posted: Sun Nov 30, 2014 11:13 am
Using the Measurement Specialties M3431 from Digikey (the 0-5V sensor in the build guide), my pressure reading is erratic at zero psi. See below plot from the log
![Image](https://lh3.googleusercontent.com/-5HoCSOOQ00A/VHtoeuuxi5I/AAAAAAAALAc/X3UMPQqv9GA/s800/logdata141130.jpg)
Bench setup, looks like this:
![Image](https://lh4.googleusercontent.com/-0d3Vtu_sJo8/VHtr3WdfC6I/AAAAAAAALAo/Wcv_qZaonVE/s800/WP_20141130_10_32_17_Pro.jpg)
In the first part of the log, the cal points are 20 psi/.489V and 480 psi/ 3.951V. It gives good values when I apply shop air pressure to the sensor, but about 20 psi low. When I put in the actual sensor calibration values, line pressure is erratic at zero applied pressure. When I apply 100psi, it settles down and line pressure = applied pressure.
Is line pressure gauge or absolute? Should I not use 0psi as a cal point?
![Image](https://lh3.googleusercontent.com/-5HoCSOOQ00A/VHtoeuuxi5I/AAAAAAAALAc/X3UMPQqv9GA/s800/logdata141130.jpg)
Bench setup, looks like this:
![Image](https://lh4.googleusercontent.com/-0d3Vtu_sJo8/VHtr3WdfC6I/AAAAAAAALAo/Wcv_qZaonVE/s800/WP_20141130_10_32_17_Pro.jpg)
In the first part of the log, the cal points are 20 psi/.489V and 480 psi/ 3.951V. It gives good values when I apply shop air pressure to the sensor, but about 20 psi low. When I put in the actual sensor calibration values, line pressure is erratic at zero applied pressure. When I apply 100psi, it settles down and line pressure = applied pressure.
Is line pressure gauge or absolute? Should I not use 0psi as a cal point?