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### Topic: stumped on a maths question (Read 1 time)previous topic - next topic

#### jonisonvespaa

##### Oct 12, 2012, 12:02 am
hi
im going to be using a pressure sensor soon, an omron D8M-A1 trying to work out the maths but hit a wall could someone tell me how to work out this figure out please

sensors output is...... 15mv    to   1247mv.
over a pressure range 0 millibar to 49millibar.

i need to know what value when @ 12 milibar,

i thought i had it but then noticed 0millibar was 15mv which threw me out

thank you

#### dc42

#1
##### Oct 12, 2012, 12:05 am
If the sensor response is linear, then it should be (12/49) * (1247 - 15) + 15 mV.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

#### jackrae

#2
##### Oct 12, 2012, 12:28 am
Delta V = 1247-15 = 1232mV
Delta P = 49-0 = 49mB
therefore Dv/Dp = 1232/49 = 25.142mV/mB
zero offset = 15mV

Therefore output at 12mB = (25.142*12)+15 = 301.71+15 = 316.71mV

But, the Dv/Dp figure of 25.142 seems rather peculiar and certainly not what you'd expect to find in an industrial environment, where manufacturers endeavoured to use "round" numbers

#### michael_x

#3
##### Oct 12, 2012, 12:41 am
Quote
25.142 seems rather peculiar

25.4 is the roundest number I ever saw

#### jonisonvespaa

#4
##### Oct 12, 2012, 12:48 am
ok here is the data sheet.

http://www.farnell.com/datasheets/91228.pdf

15 to 1247mV

0 to 4.9 kPa
(0 to 49 milibar)

#### dc42

#5
##### Oct 12, 2012, 01:06 am
So 15mV is the typical offset voltage at zero pressure. For accurate results, you will need to calibrate the sensor output  - that is, measure the output voltage at zero pressure, then subtract that voltage from the readings you get. Unfortunately, judging from the graph, the offset may (theoretically) be negative at zero pressure.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

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