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Tio Paeng

Need help reading 4-20ma pressure transducer

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I have an AB 1500 LSP and I need to maintain a steady pressure of 80psi +- 10% from an analog 4-20ma pressure tansducer. I also have a 4-20ma output proportional vent valve to exhaust pressure. Can anybody please help me out on this project. I'm a newbie and this is my first project. Appreciate all your help, Thank You, TioPaeng

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Make use of PID

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Yep, sounds like a PID loop might be in order, the thoughest part will be the tuning. There's a lot of good PID information here: http://www.controlguru.com/ If you need more specific help, we're going to need more specifics on your application.

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I am regulating air pressure in a pressure vessel. When filling, let's say from 0-70psi I want the valve to open 100% and gradually strict the flow so it does not get over pressured above 80psi. Once it's pressurized to 80psi I need to maintain it with a tolerance of +-10% anywhere from 1-24hrs. If in case the pressure goes above 10% the proportional valve opens and vents it out gradually and maintains air pressure. I spoke with my local AB distributor and he's setting me up with the material list. I know this is a difficult project and I appreciate all inputs. I'm also buying the Process Control Solutions book by John Shaw. Thanks, TioPaeng

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You only need a simple PID loop, Used the Output of your pressure transmitter, Let say scale it 0- 200 Psi is equal to 4-20mA, This is your PV in your PID loop, then scale again your Control Valve (CV) from 0 -100% opening is equal to 4-20mA , then do some fine tuning in P.I.and D, then you have a good close loop control system. your PID is Direct acting. Gnex

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