Tridium Jace Point Subscriptions

The Tridium Jace has two options for the JSON Schema output strategy, On Demand Only or COV. On Demand Only outputs the JSON messages when triggered, COV outputs messages when a point has a Change Of Value.

The COV strategy can be problematic for data analysis and where communications can intermittently fail. DCH recommends interval data and most DCH applications (at time of writing) require interval data. This introduces a problem specific to the Tridium Jace in that only the COV strategy maintains point subscriptions. If the On Demand Only strategy is utilised stale point data will be published unless a method is introduced to force point subscriptions to be maintained. There are two options:

1. Point histories

2. A second, parallel COV Schema

Setting up histories for points will maintain current values in the Relative JSON Schema messages.

For large numbers of points, creating histories for all points may overload Jace CPU and storage, and in this instance a secondary parallel COV schema can be used. The required function blocks are an additional Relative Json Schema and a Boolean Delay. This COV schema is not used for publishing and the Output slot does not need to be connected, however the schema must remain enabled and running.

Tridium Jace Parallel Schema for Maintaining Point Subscription

This Relative Json Schema is a simplified version of the main publishing schema:

· The Base Query has the same search criteria;

· The output strategy is changed to COV in the Relative JSON Schema Update Strategy Slot under Tuning Policy;

· The only field is a JsonSchema Bound Property bound to slot:out/value

Tridium Jace COV Strategy Schema for Point Subscription

This schema will maintain point subscriptions for all points in the Base Query and the JSON Schema used for point publication will publish current point values.