I am working on my first application for my city's water treatment plant and distribution system. I just noticed in the developers guide it states that digital control tags do not retain their values during app restarts. Most of our pumps are started and stopped manually and I do not want anything SCADA related to shut them down. Should I use Analog control tags set to 0 and 1 for this situation? Also do selector switch tags retain their value through restarts?

Are you talking about IO tags for a pump run command? If they are IO tags it doesn't really matter since you will re-pull the data.

If they are not IO tags and you need to record a "memory" value that keeps during restarts then you will need to use the Analog Control tag with "No Driver Selected".

In either case, if you have access to Version 12, you should use the IO and Calculation tag.

And I would recommend against using the selector switch tag as it is very limited and everything it does can be accomplished with a Digital or Discrete tag.

Basically I have configured all my pump controls with digital control tags to start and stop our distribution pumps. I want to avoid any of these pumps stopping because of an application restart. With my current configuration would a digital control tag that has been set to 1 revert back to 0 after an application restart therefore requiring the operator to manually start the pump again?

All of our pumps are controlled manually with start and stop buttons on the screen. .

I am not working in version 12 yet

Digital Control tags always indicate a value of zero. They only go high when the button is pressed. If the pulse duration is zero, you will never "see" them have a value of 1.

When you re-start an app, digital controls do not send a high pulse back out. A pump will or start or stop based on the tag value on a re-start unless the control tag has a datasource.

As Doug says, the Digital Control tag does some very peculiar things.

For Version 11, a Digital Status tag is the one you want to use for any digital IO tags unless you have a very specific use case. Plus then you get history and alarms configurable on it.

Thanks for the help, little confusing but I hope I can figure it out.

I get this. I have a similar situation at a Water Sewer district I work for.

There's a mix of RTU dummies and Click PLCs, the newer clicks have HoA functionality with the scada pushing the Water Tank Levels for the PV in a start low stop high application.

The older clicks and the RTU dummies have a Digital Control tag triggered by an expression performing a start low stop high function based on Tank Level.

This works great until the eventual hurricane knocks out the licensed radios.

The newer ClickPLC installs have a Timer that is held in by PV = PV_Last_Cycle if the timer completes the PLC runs in failsafe mode [pump stays on or pump turns off] which they have chosen by some criteria that eludes me.

Besides trending and alarming is there any other advantages to using digital status instead of digital control in V 11.3?

The only point to use a Digital Control tag (if you absolutely cannot use Version 12--if you can, use a Digital IO tag):

• If you need a pulse output (gross)
• If you need to write from Device A to Device B (gross, but also consider using Analog Control)
• If you need to write to it with a multi-write tag (then consider using Analog Control)