Pressure sensor Help

lucasromeiro · Joined: 27 Mar 2010 Posts: 167

Hello guys, okay?

I have a problem.
I have a board that makes analog readings from a pressure sensor called: mpx5050
It measures up to 5 meters of water column.
My problem is:
- Making the correct reading and processing the data read by the ADC in the water column meter (mH2O or cmH2O).
I read in several places, some say to use equation of finding two points, others speak to use the graph equation, since others speak to use a formula specifies error compensation.
But I could not do, do not know what to do.

Can anyone help me?

temtronic · Posted: Fri Sep 18, 2015 10:59 am

I've used similar sensors in the past (Honeywell as well as Moto parts).
You should run the part from a PRECISE VCC not just the PIC 5 volt supply. This will allow for a constant reading.
You should use the 2 point reading (0 and near max) as each sensor will need to be calibrated. I think 5M of water is about 8PSI differential, just a number to consider.
For testing I'd build 3 columns, 1 say with 4 inches of water (0), 2nd with 5M of water(max) and one you can vary. This way you can quickly calibrate each sensor. If only 2 or 3 sensors are needed for the project, just use nail polish on them !none=sensor #1, red =#2, org=#3 AND keep a log of the results.
When taking readings use the 'Olympic' averaging method to avoid 'bad' readings.

Jay

Ttelmah · Joined: 11 Mar 2010 Posts: 19466

I've used a lot of these sensors (and other similar variants) over the years.

Use a separate nicely smoothed 5v to feed the sensor and the Avdd pin on the PIC. Follow the decoupling suggestion in the data sheet. These are accurate to +/-2.5% without any calibration, and typically do better. You can get a more accurate result by applying a calibration, especially if the temperature range is relatively small.
You don't need a very accurate reference for this, _provided_ noise is low, and this is the same supply used to feed the PIC AVdd. The units are _ratiometric_ to their supply. However they are badly upset by noise, so keeping this separate from the PIC supply helps massively.

So you may not need a calibration at all...
Depends totally on what sort of accuracy you need?.