Control Valve Position Command Signal

G

Thread Starter

Gary

I need to manipulate a control valve's openness, but only a open loop control, not a close loop control. So a controller is not necessary, a opening signal setting device can simply do the work. What device available for use to command the signal?
 
B

Bob Peterson

Most control valves are available with a positioner. Provide an analog signal (0-10V or 4-20mA for example) to the positioner. The positioner will then open the control valve to the desired position.

--
Bob
http://ilbob.blogspot.com/
 
Gary,

If you are wanting to "...manipulate [the integrating] control valve's openness..." that you wrote about in your earlier post, then you're going to need a current source which is capable of putting out the null current (160 mA). And, as noted, increasing or decreasing the current from that value (plus the null "bias") will only change the rate at which the valve moves. Since YOU will be controlling the position ("closing the loop") you will need to be able to change the current back to the null value (plus the null "bias") to get the valve to stop at some position.

If you're talking about some other valve, well, then you're going to have to tell us a lot more about the valve actuator/positioner.

There are LOTS of actuators/positioners that use all manner of signals (DC voltage; AC voltage; DC current; AC current; digital signals (proprietary and other protocols), so when asking a question like this please tell us about the valve's actuator/positioner and what it requires and we can provide a more concise response (instead of guessing).

I think what you might be able to do that's even simpler is simulate the 4-20 mA input to the SPC and let it do the signal to the valve. 4 mA would be 0%, 12 mA would be 50%, and 20 mA would be 100%. That way you could test the SPC and the integrating actuator--and a 4-20 mA source is much easier to find and use. When you have an integrating controller it's very difficult to control position using a simulator--especially when there's a null current involved. It can be an exercise in futility to try to control an open-loop integrating controller, or one with no feedback. And, it can be very misleading if you're working by yourself for the first time without the benefit of someone's who done this once or thrice.

Please write back to let us know how you fare--and if you're talking about a different control valve that you want to manipulate the openness of. ;-)
 
This post of mine is not related to my other post about the integrating actuator TM-55. Sorry for the confusing caused by TM-55 post.

My question for this post only relates to a globe control valve with pneumatic actuator and valve positioner. I need to throttle the openness of the valve as per the commanding signal issued by operators. Therefore it is not a close loop control, and PID controller is not necessary.

But I need a device that can manipulate by operators to issue the valve opening demand signal, such as 4-20 mA simply corresponding to 0-100% valve openness. What kind of device normally used in this kind of application? I need a commercial out of the shelf device.

Thanks for responding.
 
just put your controller in manual and adjust the output

> I need to manipulate a control valve's openness, but only a open loop control, not a close loop control. So a
> controller is not necessary, a opening signal setting device can simply do the work. What device available for use to
> command the signal?
 
R
I believe you are looking for a Manual Loading Station, I haven't seen one for years.

If you are using a DCS or PLC just use a PID controller locked in Manual Mode, there are several ways to set one up to do just that.

Roy
 
I think Roy got it - manual station. I thought almost any PID controller had an auto/manual or hand/auto mode switch, but maybe not. Sometimes the HMI for PLC or DCS doesn't implement it.

If you're still looking, the guys in the mills use the Honeywell UDC 2500 current output controller (with the optional lower display and manual option).

They configure them to power up in manual mode, then they disable the auto/manual key/button (configuration setting) so the controller is locked in manual mode. The display reports "key error" if someone presses the auto/manual button.

They say they like it because the relatively large up and down arrow keys make it easy to change the output value when they're wearing gloves and the lower display shows the output percentage as a digital number, so there's no personal interpretation of "how far to rotate the pot knob"; the output value is easy to read as a digital number.

It amazes me how many manual stations there still are, even though they do some remarkable control with their PLCs in other areas. Go figure.
 
the correct terminology is

Remote/Local for the Setpoint Adjustments

Auto/Man for automatic control or manual output adjustment

Manual loading stations are still common even in DCS, in cases where closed loop (single or multivariable) control is not warranted.


 
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