The Utilizes reference is often used in conjunction with shared resources.
In the example below we have a power supply unit with a single power output.
Three devices are connected to that output and therefore share that resource.
This is modeled by Utilizes references.
The references now can be used to aggregate information for resource planning.
If you have to select a replacement PSU during repair, you can follow the Utilizes references pointing to the power output in reverse to find the power needs of the three devices and aggregate them to get the requirements for the power supply.
But not in all cases resources are directly used, there could be hidden indirect relations.
A lighting controller often controls an LED lamp by modulating the electrical current to the lamp.
Although there is no direct cable connection between lamp and PSU the lamp is indirectly supplied by the PSU. Normally the power need of the lamp therefore is incorporated into the power need of the lighting controller.
If it is instead needed to explicitly model the relation between lamp and PSU this can be done by adding an additional Utilizes reference (dotted line).
Please be aware that an OPC UA reference cannot have additional parameters. It is simply there or is not there. Therefore, by browsing the references a client cannot distinguish between a reference modeling a direct or indirect relationship (solid line vs. dotted line).
If this is needed a reference refinement must be used to further describe the nature of the dotted Utilizes reference.
Figure 61 – Reference Refinement of the Utilizes Reference
ReferenceDescription Value of IndirectUtilisation
SourceNode:Lamp1
ReferenceType:Utilizes
IsForward: TRUE
TargetNode:PowerSupply1
ReferenceRefinement of IndirectUtilisation
{
ReferenceListEntry
ReferenceType:Controls
IsForward: FALSE
TargetNode:LightingController1;
ReferenceListEntry
ReferenceType:Utilizes
IsForward: TRUE
TargetNode:PowerSupply1;
};
The refinement allows to give an ordered list of references (a path) that are simplified by the reference the refinement belongs to.
The dotted Utilizes reference is a simpler model of the real path that leads from the lamp to the power supply. In reality, Lamp1 receives its power from the lighting controller (which is expressed by the Controls reference from lighting controller to lamp) and the lighting controller gets its power from the power supply.