George’s CBAS Tips, September 2019


What is Priority in CBAS?

When you look at the list of points, either in Text View or Hardware View, you see the point name on the left. To the right of that is the status of the point, and to the right of that is the priority of the point.

Status is either the value that the sensor is sending back or in the case of an output, whatever the point was commanded to. Priority only applies to outputs, because inputs cannot be commanded. 

In the picture above, Tower Mode has no priority, so it is either an input or it has been put into “auto” and nothing has commanded it since. When you click an output point and click AUTO, it removes the priority until something else commands it. That something could be one of many things:

  • OPER means an operator (someone at the computer) has commanded it. This priority means it is no longer automated because OPER overrides most logic and all schedules.
  • SCH means it was commanded by a schedule residing on the point. Schedules only evaluate and command once a minute. It doesn’t get commanded if it is already in the scheduled state.
  • LOG1 means it was commanded by Logic Level 1 residing on the point or another point. Unless the conditions of the logic are met, the point is not commanded and the priority will remain blank if you put into auto.

As you can see, some priorities override others and that’s why it’s called priority. To see what overrides what in CBAS, go to Text View, then Priority Summary.

Notice that Weekly Schedule is the lowest priority and everything else can override it. Also notice that a few other schedule type features can override it also, like Optimal Start, Holiday Schedule, and Overtime. When these features finish running, they AUTO, allowing the Schedule to take over again.

7, 8 and 9 have to do with PIDs which command analog outputs like chill water valves and dampers. 8 and 9 have to do with auto-tuning a PID, which is a feature on the PID Program Screen. This is designed to optimize the settings of the PID.

Logic 2 can override Logic 1. The reason for this is if you need to use one logic statement for one situation and another to override that in another situation. Once the conditions are no longer met for that second situation, you must write the logic to AUTO the point so that the lower priority logic can take over again.

Notice that the next three are all priority level 12. That means they can override each other because they are equal, and they can override everything else that is a lower priority. They are all operator commands from different sources: CBAS Web, CBAS, and the Handheld Programmer that plugs into an X or LX controller.

The final thing to understand is that the only priorities that can override the Operator Priorities are Logic 3 and Logic 4. If you have a critical point that you don’t want OPER to override, you make your logic level 3 or 4. 

One other thing about Priority Summary is that you can click on these priorities on the list and see what points are commanded by that priority. So if you want to see every point that has been overridden by OPER, click it. It will be mostly setpoints, but you might find a valve, damper or AHU fan start/stop point in that priority.

More to explore