I had a PC Mountable Wet/Wet Differential Pressure Sensor I used it to measure a pressure difference , I don't know how to convert its output to pressure !
Well, it looks like your sensor is +/-5psid (based on the link you provided), so looking at the datasheet, we have (assuming a 10VDC excitation) 16.7mV at 1psi and 50mv at 5psi. Assuming the sensor is linear (the datasheet states that linearity is +/-0.25% of full scale), you have the following relationship:
P = V * 0.1201 - 1.006
P is expressed in psi and
V in mV. This does not take into account any possible hysteresis (0.2% of full scale according to the datasheet).
If you want an accurate reading, you should probably do your own calibration by applying a series of known pressures (measured with a calibrated instrument, e.g. manometer) and reading the sensor output.
How did I arrive at the relationship? It's fairly easy, you're fitting a straight line to two points, so you're looking for a slope and an offset:
1psi = 16.7mV * slope + offset 5psi = 50mV * slope + offset
That's 2 linear equations with 2 unknowns (
offset), which is easily solved to give the values mentioned above. That's really basic maths though, I would expect any engineer or even technician to know how to do that, which is why I hadn't included the details on how to calculate the values in the first place.