Controlling from External Masters using Priority Array

The priority array is a mechanism to support multiple masters in a given system. Normally a controller will be in charge of the outputs on board itself. Occasionally you may want to override the outputs from the logic running in an external master controller, perhaps to do morning startup or load shedding. In emergencies there may be a smoke evacuation mode managed by a fire control system.

Priority arrays are read only, if you would like to change the value of an output you write to the present value and specify the priority at which you are commanding that output. The T3 controller will automatically add the entry to the priority array and command the output state using the highest priority entry in the table. Entries higher up in the table override the lower priority entries.

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As an example of the priority array in action, here’s what the priority array will show when the
the hand-off-auto switch on the front cover of the controller is flipped to manual on,

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And when the operator using T3000 front end sets an output to manual OFF, the priority array will reflect that like so. Since priority level 7, the hand-off-auto switch says on, the output will still be on. The Auto/Manual operator telling the output to go OFF at level 8 is overridden.

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Here is a screen shot of priority array in action as viewed from the free and very handy Bacnet Discovery Tool from Contemporary Controls at Tab1 and issuing a command to turn Output 1 off at Priority Level 9. On the right is the view of that same Output 1 using the T3000 -> Tools -> (Yabe) Bacnet tool showing the results of the command, Priority Level 9 correctly shows the off state. To clear the priority level 9 command you would write a value of 255 after which the output would revert to the Level 8 state which also happens to be off in this example.