In ABB Advant AC450 DCS System, we got the Function Unit PIDCON.
What's the difference between Balance mode and Manual Clamp mode?

 

I would love to know this, I can't find this info anywhere. You ask ABB and it's always the same "sign up for the class".....

If you could help me out I would sure appreciate it.

>In ABB Advant AC450 DCS System, we got
>the Function Unit PIDCON.
>What's the difference between Balance
>mode and Manual Clamp mode?

 

cut from the Pidcon Users Guide:
<i>
When the controller is operating in the BAL (BALance) control mode, the output signal follows a balance reference signal which is connected to a PC input. The operator cannot command the BAL control mode from the keyboard. The command is received either from an external control device or from some other PC element.

The BAL control mode is used when the control signal is disconnected and the controller is to be balanced for bumpless return.

The function obtained with clamping (CLAMP) is the same as that obtained with control mode E3 except that the priority allocated to clamping is higher. This means that the operator cannot control the output signal of the controller when it is clamped. The clamping value consists of a signal received from an external source. The output signal is force-controlled, following a ramp function, to the clamping value. The MAN control mode returns when the clamping function is deactivated. The output signal remains at the clamping value until the operator makes a change. Clamping of output signal value is used when the output signal is to go to a predetermined value when a certain event occurs.
</i>

 

This diagram might help as well.

http://riscy.biz/files/images/PIDCON.GIF

Chris Jennings

 

Really appreciate the response. If I fed the PV into the balance reference then when I return to auto from balance it should be smooth or am I screwed up?

 

I would have thought that because the Balance reference is going directly to the Control Output block in the PID calculation that it wouldn't be bumpless. The only smoothing that would be applied would be from any control action rate limiting (P.S. I'm writing this at home so I can't check the manual).

Do you happen to have a test controller that you can trial your logic in. Theory is great but nothing beats an experiment.

Chris Jennings

 

> Really appreciate the response. If I fed the PV into the balance reference then when I return to auto from balance it should be smooth or am I screwed up? <

You don't feed the PV into the BalRef - You Feed the Actuator Position into the BalRef. Returning from Bal mode leaves the controller in Manual so there is no Auto control action to "Bump" the output. What happens when you then go to auto mode depends on how your setpoint has been tracking while in Manual mode.

Rob
www[.]lymac.co.nz

 

Thanks much for the help everyone, it would appear there is enough information to try a test out. I would like to respond back with my test results (if there is anything worth reporting) although it will take some time to get setup.

Chris