PI APS configuration for interfaces with multiple instances

On a PI Server where multiple instances of an interface are collecting data from one data source, special care must be taken when registering these interface instances with PI APS to avoid the problems discussed in this section.

Data source with multiple interface instances

The following figure shows a set diagram of a data source with multiple interface instances. The large outer ellipse represents the set of tags in the data source. Each inner ellipse represents the existing points associated with an interface instance. The shaded area, which is not to scale, corresponds to actual available points in the data source.

Each PI APS instance identifies its specific existing points and the corresponding data source tags using the same procedure as the associated interface instance. Multiple interface instances result in two related problems for PI APS with respect to available points. (These problems are unique to PI APS because the actual interface instances ignore the available points.) The problems result from the fact that each PI APS instance assumes that it manages all tags in the data source on behalf of its associated interface instance. If the PI APS instances are not properly configured, the PI APS instances can create multiple PI points for each data source tag. The following sections provide configuration rules for avoiding multiple PI points.

Rule 1: Configure each PI APS instance so that only one of them manages any specific available point

Each PI APS instance assumes that it manages all tags in the data source on behalf of its associated interface instance. Consequently, if n interface instances are registered with PI APS, the first problem is that each PI APS instance creates a point for each available point, resulting in n new points instead of one. To ensure that only one PI point is created for each data source tag, you must configure the PI APS instances so that only one of them manages each available point.

Rule 2: Configure each PI APS instance to ignore the existing points of the others

PI APS instances are unaware of each other. That is, when multiple interface instances for the same data source are registered with PI APS, the existing points for one interface instance are perceived as available points to the other PI APS instances. For example, the shaded area in the following figure shows the available points from the perspective of PI APS instance 1.

Available points for interface instance 1

To prevent one PI APS instance from creating PI points for the existing points of the other instances (resulting in multiple PI points for one data source tag), you must configure the PI APS instances to ignore the existing points of the other interfaces.