Ramiro Posted February 3, 2020 Report Share Posted February 3, 2020 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 Quote Link to comment Share on other sites More sharing options...
MVP 2023 Flex727 Posted February 3, 2020 MVP 2023 Report Share Posted February 3, 2020 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? Quote Link to comment Share on other sites More sharing options...
sgull Posted February 3, 2020 Report Share Posted February 3, 2020 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 Quote Link to comment Share on other sites More sharing options...
MVP 2023 Ausman Posted February 3, 2020 MVP 2023 Report Share Posted February 3, 2020 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 Quote Link to comment Share on other sites More sharing options...
MVP 2023 Joe Tauser Posted February 3, 2020 MVP 2023 Report Share Posted February 3, 2020 You may want to go back and look at the accuracy specs on these modules- 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. Quote Link to comment Share on other sites More sharing options...
Ramiro Posted February 4, 2020 Author Report Share Posted February 4, 2020 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 Quote Link to comment Share on other sites More sharing options...
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