Regarding the control issues of control valves
Thread Content
Our company is currently planning to install a control valve, which is mainly used for controlling the opening degree of manual valves. It is desired to be able to manually adjust the valve opening on-site, as well as adjust it from the control room. May I ask if it is sufficient to purchase a 2-channel PID module in order to connect the 4-20ma signals to the signal lines in the control room? If that’s not possible, how can it be achieved? Thank you very much
This can be done by installing a PID regulator on-site; its output is connected to an on-site/remote switch, and the signal from the DCS is also connected to this switch. The output of the switch is then connected to the valve positioner. When the switch is set to remote mode, it is controlled by the DCS; when set to local mode, it is controlled by the on-site PID.
But the downside of this is that I can no longer monitor his on-site operation of the opening degree
What do you mean by manual valve opening control? ?
It involves installing a PID controller on-site, which allows for the input of the valve opening degree when in manual mode
Typical PID secondary controllers have a manual/automatic mode switch function. You simply connect the DCS signal to the secondary controller and set the parameters accordingly. If you want the DCS to display the valve opening degree, it is necessary to ensure that the on-site locator provides feedback on the valve position; by connecting this valve position feedback to the DCS, it will be possible to display it there. :lol
Buy a control valve with a handwheel and a valve position transmitter. Whether it is manual operation on-site or remote control from the control room, the control room can then see the changes in valve position (either through manual operation or remote control from the control room). It is not possible for a control valve to be manually controlled on-site while also being remotely controlled from the control room.
The valve actuator uses a 4-20ma cable for control feedback; can this be achieved by connecting it in series to a PID controller?
By manual control, I don’t mean a handwheel; rather, it refers to installing a secondary PID controller on-site. By connecting the 4-20mA cable from the valve positioner to both the DCS and the on-site PID controller, it becomes possible to control and monitor the system from two locations, with both forms of control being carried out using hand operators
The control line requires 2 wires, and the feedback line also requires 2 wires； If there are only 2 cores, it means that no feedback signal is being collected; serial connection is generally not possible in such cases