All equipment configured in the DeltaV Explorer is assigned a unique equipment ID. The DeltaV system uses this ID to allocate equipment and service any requests for ownership. The term arbitration refers to how something with an equipment ID (usually an equipment unit) is owned and released through different stages of a recipe. You can also assign equipment IDs to control modules and unit modules to allow them to participate in arbitration.
In the paint tutorial example, both blenders are filled from the same color tanks, but only one should be filled at a time so that two colors are not in the same pipe. The modules for the inlet valves, XV_COLOR_500 and XV_COLOR_600, will be tied together so that only one can be used at a time. To do this, you will create a control module named COLOR_HEADER that will list the two modules as Equipment Needed. Only the phase that has acquired the COLOR_HEADER resource will be able to open and close the valves XV_COLOR_500 and XV_COLOR_600.
Before creating the COLOR_HEADER module, you will modify both XV_COLOR_500 and XV_COLOR_600 to allow them to participate in equipment arbitration. This makes it possible to add them to the Equipment Needed list for the COLOR_HEADER module.
After you have set up the modules for equipment arbitration, you will create the phase coordination through a phase class for charging color into UM_BLEND_500. The phase logic will:
- Request (through a phase REQUEST) acquisition of the COLOR_HEADER resource
- Open #COLOR_IN_VLV#, the alias used to identify valve XV_COLOR_500 or XV_COLOR_600
- Release the COLOR_HEADER (through another REQUEST message) when the blender is finished filling
From the time the COLOR_HEADER is acquired until it is released, the second color input valve can only be manipulated by the owner of the COLOR_HEADER, which in this case is the phase logic running on UM_BLEND_500. (An exception is that the valve may also be opened or closed through direct intervention by an operator with sufficient privileges).