GSK72 (Customer) asked a question.
BRX PID valve shut off.
Hi,
To give you an idea, I am using a control valve with a 4-20mA control signal. I have been reading and watching the videos about the BRX PID control system, but there is something that I have not seen or can find. The valve is used to control the amount of liquid in a vessel. In the case that the operators decide to close the valve. Is there a way to do that in the BRX that is simple while having the valve's position being controlled by the PID loop?
Is it like using a contactor to open the PID loop and then manually setting the position of the valve?
Any advice would be great!
Commonly the PID is placed in manual mode. This then allows the output to be adjusted manually or by other PLC logic. Once the PID is in manual you can send a "close" signal to the valve. When the PID is changed back to auto mode the PID continues adjusting the output.
Yes! The PID View's Form section lets you override the mode and then easily set the .Output value for that PID element from the form.
However, if this is "normal" use case, you need to be able to drive the input leg of the PID instruction that gets set ON to request AUTO mode and set OFF to request MANUAL mode using some combination of contacts driving the PID rung.
Once the powerr flow is OFF into the PID instruction, the PID struct's .Output member can be modified via logic or HMI or whatever. Remember it's a percentage value, so 0.0 to 100.0.
I don't see in the documentation on how to be able to set a close single with the PID in manual mode. Can you send something that could tell me how to do that? I was thinking about switching the PID to manual mode and then setting a move block to the analog output and having it set the output to 4mA.
You could simply switch the PID to manual mode, then use a move block in logic to set the analog output to 4mA. Give it a try.
That is what I am thinking of doing. If there is a proper way to do that, I'd rather do that.
I really like how they made the BRX PID function, very easy and flexible (compared to DL). To implement what you are asking, and what was explained, we like to make a PID screen on the HMI, similar to the screen print. This includes a Hand-Off-Auto function. With a H-O-A, the operator can close the valve with Off, set a valve position with Hand (0-100%), or run the valve on PID. The trend graph shows the response needed for tuning. The Bias display is helpful for evaluating the "I" term. The numeric entries allows adjustments of P,I, and D (if D is used). Some Login scheme and/or pass codes should be used to limit access to the adjustments.