control valve

could you clarify your question? I think I can answer you question, but need a little more clarification. What type of valve? Is it controled by an analog (4-20mA) signal or a digital (120VAC) signal?

The most common method is to use an analog output 4-20 mA from the PLC to a motor operated valve with a 4-20 mA positioner. The valve will track the signal - 4 mA closed (usually) 12 mA = 50%, 20 mA 100%, etc. You control the PLC output with your logic.

jjnelson81 said:

could you clarify your question? I think I can answer you question, but need a little more clarification. What type of valve? Is it controled by an analog (4-20mA) signal or a digital (120VAC) signal?

Click to expand...

Fisher control,
type:67AF&67AFR filter reglator.
controled by an analog(4-20mA)SIGNAL

Fisher control,
type:67AF&67AFR filter reglator.
controled by an analog(4-20mA)SIGNAL

AZIZ, you accidentally started two theads on this topic. If you have not seen the other thread it is here:
http://www.plctalk.net/qanda/showthread.php?t=38328

The 67FR or 67AFR is a filter regulator used to supply air to a control valve or positioner. It does not have a 4-20ma signal, but the device it is mounted on may very well have a 4-20ma signal.

Tom's description of operation still applies.

Sorry I am so slow, stuck in New Jersey. Tom is spot on.... with a SLC processor you will need to use analog cards to do all the control and feedback to and from the valve.


The one thing Tom left out is the raw data that the SLC processor uses to reference the 4-20mA signal. For an analog input card (1746-IF8)the raw data is 3277 (4mA) to 16384 (20mA). The actuator should have a position feed back so you can track the valve position (maybe not).

For an analog output card (1746-NOI4) the raw data spans 0-21mA..... 0mA=0 raw and 21mA=32767 raw. For a 4-20mA signal, the raw would be 6242-31208 respectively. Ths would be used to control that actual position of the valve.

If using an HMI to enter a setpoint, you would probably want to enter it in a percentage (0-100%). In the PLC you would then put you setpoint into a SCP (scale with parameters) command. The input being the setpoint, the min and max raw would be 0-100. The min and max inEU (EU stands for engineering units) would be 6242 and 31208. The output would be tied to the actual output card to the valve. The SCP will scale the 0-100 setpoint to a raw value that the valve will understand. 0% would be 6242 and 100% would be 31208 (4-20mA).

You can manipulate the setpoint in the program with algorithyms or PID loops, this is how we apply this.

Hope this helps, hit me back if I have missed something.

-J