Pressure sensor Maths

Projects General Guidance
1

Hi.
I am puting together the pressure sensor bit into my code.
Below is the data on the sensor I will be using.

Pressure sensor. http://www.digikey.co.uk/productdetail/en/2000131/MSP3101P2-ND/206884
Pressure Type Gauge
Operating Pressure 100 PSI
Port Size Male, 1/4" (6.35mm) NPT
Output 0.5 ~ 4.5 V Ratiometric
Accuracy -
Voltage - Supply 4.75 V ~ 5.25 V
Termination Style Cable
Operating Temperature -20°C ~ 85°C
Package / Case Stainless Steel

A few Facts on the related subject..
100 psi. = 231.2926 feet = 70.4981 metres of water
Seawater is about 1,030 kg/m3
MPa (Saltwater) = 0.1013 + (0.01 * DepthMeters)
100 psi = 6.8948 Bar
1 psi = 0.07032496149 meter of water

Am I correct in working out the pressure sensor pressure to depth in metres.
0 volt 0 adc
.5 volt. 102.4adc. 0 Metres
1 volt. 204.8adc
1.5 volt. 307.2adc
2 volt. 409.6adc
2.5 volt. 512adc. 35.246 metres
3 volt. 614.4adc
3.5 volt. 716.8adc
4 volt. 819.2adc
4.5 volt. 921.6adc. 70.49 metres
5 volt. 1023adc

The simple way from adc value AVCC = 5 Volt
0.5 v = adc_value 102.4
4.5 volt = adc_value 921 .6
So 921.6 - 102.4 = 819 Total range
Total range / 70.4981= 11.617334367
adc_value- 102.4 / 11.617334367 = Depth in meters

Depth = analogread(A0) - 102.4 / 11.617334367;
The question is I'm I right in what I am doing???
Regards Antony

2

I think one problem is that you have a "Gauge" pressure sensor which measures pressure relative to AMBIENT pressure. I think your calculations will be correct if the vessel containing the sensor is at 1 Atmosphere and does not compress at all under water.

I think you would be better served with an "Absolute" pressure sensor. It will read about 1 Atmosphere at sea level.

3

Hi.
If I use absolute pressure sensor then I would need to subtract the one atmosphere in the calculations.
The RoV is Non compressible (I hope).
Thanks for the reply.

Regards Antony.