PID controller/plc??????

niklad13 · Feb 4, 2008

hi all
i am facing really a strange problem due to my plc and/or PID controller applicatin.

i am working as a mechanical engineer and i want to automate a testing process of pressure reagulator. the input will be different presssure values. based on this pressure value over certain time period, regulator will pass/fail the test procedure. i had very few idea of using PLC so i bought the book available online here and went through. but i couldnt figured out that how plc will understand various singal produced by analouge/digital pressure tuansducer in the form of ladder logic?

or is that something thats called PID controller i am looking for?

can anyone suggest anything really helpful???

SteinCollector · Feb 4, 2008

Depends on the outputs created by the pressure valve, and the accuracy required. You will need analog inputs to read the valves. The are input modules or PLCs that can understand 0-10VDC inputs, 4-20mA, -10 to +10 VDC, etc. You get the idea. You need to pick your parts to match what the valves output. The outputs will create a range of numbers inside the PLC. In certain Mitsubishi parts, for instance, 0VDC creates a value of 0 in a data register, while 10VDC creates a value of 4096. 5VDC (half full value) creates 2048 in a data regsiter.

Mitsubishi has a product called the Alpha that is cheap and includes analog inputs - I don't recall if it's 0-10 or what. But most companies make basic level products that do what you want

niklad13 · Feb 5, 2008

SteinCollector said:
Depends on the outputs created by the pressure valve, and the accuracy required. You will need analog inputs to read the valves. The are input modules or PLCs that can understand 0-10VDC inputs, 4-20mA, -10 to +10 VDC, etc. You get the idea. You need to pick your parts to match what the valves output. The outputs will create a range of numbers inside the PLC. In certain Mitsubishi parts, for instance, 0VDC creates a value of 0 in a data register, while 10VDC creates a value of 4096. 5VDC (half full value) creates 2048 in a data regsiter.

Mitsubishi has a product called the Alpha that is cheap and includes analog inputs - I don't recall if it's 0-10 or what. But most companies make basic level products that do what you want

thanks for your suggestion.
so please tell me how small value of VDC or mA a PLC will recognise?
for example in the range of 0-10VDC, how many different value it can read like 1,2,3,4,....or 0.1,0.2,03,0.4,.......likewiese.
i havent figured out how much accuracy i need but my applicaiton is very sensitive. the worst case is controlling 3500PSI to 10PSI. means input to regulator will be 35oo PSI and output(set point) will be 10 PSI.

and finally how can i create logic for the rules that regulator must follow in order to pass.(i have physical rules but how can i cast those rules in ladder logic?)

output of PLC is just pass/fail(red or green LED)

thanks again for your help

harryting · Feb 5, 2008

Depend on your field device and PLC analog input card. I would read the manual on both.

You need to have much better (detailed) description of your process for us to be of any help to you.

is this an existing process/machine or are you creating something from scratch?

Thomas · Feb 5, 2008

Unless you have some time to learn the concepts and equipment, you may want to talk to a system integrator in your area.

PID controller/plc??????

niklad13

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SteinCollector

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niklad13

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harryting

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Thomas

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