# Scaling of digital reading of pressure sensor

I have purchased one of these and I've connected it to a pressure sensor. I now need to convert the digital values to pressure. However, my maths is all forgotten. Can anyone help me out?

The discrete values I get back from the sensor are between 0 to 3750. 750 is equal to 0 bars pressure. The top pressure the sensor can goto is 250 (which is 3750) and the values are linear.

Any help appreciated.

• Hello, since I didn't know what "4 to ma" was going to say I have tried to edit your title to be more descriptive. Feel free to change as you see fit. – Ghanima Oct 11 '18 at 17:37

Linear for the win!

y = (slope * x) + intercept is the classic linear formula, in your case, x=sensor, y=bars, so the formula becomes

``````bars = (slope * sensor) + intercept
``````

... and you have two data points of this formula, sensor@750, and sensor@3750

``````equation 1: 0 = (slope * 750) + intercept
equation 2: 250 = (slope * 3750) + intercept
``````

... lets rearrange the 1st equation in terms of the intercept, so

``````- (slope*750) = intercept
``````

... and use this intercept equation in the 2nd equation, so

``````250 = (slope * 3750) + (-(slope*750))
``````

... continue by solving for the slope

``````250 = 3750slope - 750slope
250 = (3750 - 750) slope
250 = 3000 slope
250 / 3000 = slope
1/12 = slope
``````

... use this in equation 2 to find the intercept

``````250 = (1/12 * 3750) + intercept
250 - 312.5 = intercept
- 62.5 = intercept
``````

... and you have your final conversion equation!

``````bars = (sensor / 12) - 62.5
``````

Which is valid with the 2 examples you started with.

since a picture is worth a thousand words: 