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I'm use a V350-35-T2 and IO-AI4-AO2, and connect a pressure transmiter (2 wires) to AN0 (V350) (10 bit), the pressure transmitter range is 0-10 barg 

I configured the MI0 with parameters: 204 to 1023 and 0 to 1000 

At atmospheric pressure the measure should be 0 barg/204 but in online test the measure of count is 203

I connected an ampherimeter to measure the real current and it measure 4 mA (in online test I read 203 count)

I changed the connection of pressure transmitter to AI0 (12 bit) (of IO-AI4-AO2) and parameters now are: 819 to 1095 and 0 to 1000

I read at 4 mA 816 count, it is not correct measure (819)

Any explanation about it? solution? 

Thank you

PD: Excuse me about my bad English

 

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26 minutes ago, Ramiro said:

I connected an ampherimeter to measure the real current and it measure 4 mA (in online test I read 203 count)

The reading of 203 would be a measurement of 3.995mA. Is 0.005mA really a concern to you?

27 minutes ago, Ramiro said:

I read at 4 mA 816 count, it is not correct measure (819)

This reading is only off by .004mA.

This all sounds really accurate to me. What is the issue you're having?

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for 12 bit it should be 819-4095

How accurate is your pressure transmitter and meter?

This does not seem to be a huge difference.

You can always do a small calibration routine in the program to create an offset

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This is one of the reasons I made this Excel sheet:

http://forum.unitronics.com/topic/3540-linearization-calculator-for-all/

For anything analogue that is showing "linear" input behaviour, but is slightly "off" in readings, the above sheet lets you easily adjust numbers to suit your needs by changing appropriate numbers and seeing final output very easily so that you can get things almost perfect.  Sometimes I have used a few linearizations in a series type setup, where the input is not completely linear but has slight changes to the curve over the input range. 

In "Utopia" land at Universities, everything is exactly  as specified.  Sadly, in the real world, slight discrepancies are common place and have to be allowed for.  Anything with a large discrepancy indicates a problem.

cheers, Aus

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You may want to go back and look at the accuracy specs on these modules-

image.png.4e807f2909907819206476be66bac8f4.png

 

Translate this as +/- 5 counts on the A/D converter is within specification.  The error will generally be very repeatable - Ausman and sgull have mentioned the best practical solution of just accepting some inaccuracy and programming around it.

These aren't lab instruments.

Joe T.

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Firstly, I want to thank everyone who answers very kindly,

I will follow your advice to do a small calibration routine to create an offset
 
Thank you, 
 
Ramiro
 
 

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