4-20mA pressure transmitter programming problem
4-20mA pressure transmitter programming problem
(OP)
I am trying to use a Rockwell SLC 5/03 to program a pressure transmitter to open and close a valve with a 4-20mA signal. The PLC is reading the signal, but I need to reverse it so that a 4mA signal input creates a 20mA signal output. I am trying to fill and empty a tank of water without it overflowing. The a high signal is being sent to my pressure transmitter when the tank is full and I need my I/P converter to close my valve at this point. As it stands, the I/P converter is reading a 20mA signal when the tank is full and opens the valve. I need this to be reversed, which is why I am utilising the PLC. I have tried many things and have failed to reverse the signal. Any help or insight would be greatly appreciated.





RE: 4-20mA pressure transmitter programming problem
RE: 4-20mA pressure transmitter programming problem
Convert the 4-20mA input to 0 - 100% or 0.00 - 1.00
Then do the math statement:
one minus [input in percent] = [output in percent].
example:
The input is at 8.0mA or 25% of span.
When input is at 25%, the output should be 75%
math: 1 - 0.25 = 0.75 or 75% output (16.0mA) to the valve.
RE: 4-20mA pressure transmitter programming problem
4095 - (Analog Value )
4 - 20 mA = 0 - 4095 counts so...
4095-20mA(4095) = 0(4 mA o/p)
4095 - 4 ma(0) - 4095 (20 mA)
Copy the result to your AO point.
RE: 4-20mA pressure transmitter programming problem
RE: 4-20mA pressure transmitter programming problem
RE: 4-20mA pressure transmitter programming problem
RE: 4-20mA pressure transmitter programming problem
RE: 4-20mA pressure transmitter programming problem
What you need is a PID loop so you can set the gain and integral action.
Roy