Why a station polls too slowly

Each field-bus driver network carries a polling service — named Poll Service or Poll Scheduler depending on the driver — and it samples values at exactly three rates. The shipped intervals are:

There is a fourth group that is easy to miss: Dibs Stack, which handles pollables that transition into a subscribed state — the temporary subscription created when somebody opens a graphic, for instance. It is why a station can look responsive while an operator is watching and still be logging stale data the rest of the day.

This differs by driver, and it is the part that catches people moving between them.

• Under a BacnetNetwork, the poll frequency is a property of the tuning policy, and each proxy point is assigned a tuning policy. You do not set a rate on the point.
• Under most other drivers, Poll Frequency is a property of the point's own proxy extension, and of the device object where a device is pollable. It sits just below the address properties.
• The NiagaraNetwork does not poll points at all. Station-to-station values arrive by subscription, so a slow Niagara Network is a different investigation entirely — look at its tuning policy's update times instead.

A driver's Tuning Policy Map ships with one default policy, and a station built without touching it has every point in the building on that one policy. Tridium's own documentation is unusually blunt about this: using only the single default policy, particularly with all property values at defaults, can lead to problems in many scenarios.

The fix is not clever. Duplicate the default policy three or four times, name the copies after what they are for, set their poll frequency, and assign points to them as the points are created. Done at engineering time it costs nothing. Done afterwards it is a bulk re-assignment across several thousand points, which is a different note.

The polling service publishes its own statistics, and they answer the question directly rather than by feel:

• Busy Time — the percentage of the time the station spent polling. This is the number that tells you whether the bus is saturated or the problem is somewhere else entirely.
• Average Poll — the average time spent in each poll.
• Total Polls, against the elapsed milliseconds.

Right-click the poll service and use Actions > Reset Statistics to start a clean window before and after a change, so the comparison is between two measurements rather than between a measurement and a memory.

One caveat on reading them: the BACnet driver polls on multiple threads — two per network port — and the statistics are the sum across all of them. There is no per-thread breakdown, so a busy figure on a station with several trunks tells you the station is busy, not which trunk is.