SeventyFiveF Niagara Driver: FAQs on Reading Points

Using the default settings, how do point reads work?

By default, points will read from the 75F cloud once per minute.

Once per minute. Can I change that?

Sure! Go to the Poll Scheduler property on your SeventyFiveFNetwork. You will see a Fast Rate, Normal Rate, and Slow Rate for polling:

These rates work together with the Poll Frequency property on each SeventyFiveFSite:

Right now, this site is set to read at the Fast poll frequency, and Fast currently means "once per minute". Changing the Poll Frequency to Normal would change the read interval to "every five minutes", unless the Normal Rate property was adjusted on the SeventyFiveFNetwork.

By adjusting the polling rates at the network level and the Poll Frequency of each site, you can tune the read intervals to whatever you want.

(Note: data is updated in the 75F cloud once per minute. So, setting your SeventyFiveFSite to read more often than that will not get you fresh data any faster. It'll just make your station work harder than necessary.)

Seriously? Does polling need to be that complicated? Why are there two layers of parameters instead of a single setting?

It does need to be that complicated, in order for all Niagara drivers to look roughly the same.

Device polling is one of those things that is standardized across drivers. For some drivers, users need to be able to fine-tune traffic on a per-device basis, like on a crowded BACnet trunk.

The trade-off is that all drivers need to implement this functionality, even if they don't require it.

That's why there is an option to have multiple 75F sites in a station all tuned differently, even though it's almost never going to get used.

When I open up a new folder, why do my points remain stale for a minute or so before loading? BACnet, NRIO, and (pick an OEM's proprietary serial protocol from the 1980s) load points within a few seconds.

The 75F driver implements polling a little differently than most: it doesn't poll points on an individual basis. When a site is polled (according to the Poll Frequency of the site), it makes one big API call that fetches all points from the site that currently need updating.

Which points currently need updating? The station actually decides that, not the driver. This concept is called subscription in Niagara. Basically, a point will be subscribed if:

• Something in the station needs to know its current value (e.g. a linked component or a history extension).
• The point is part of a view that is currently being looked at by a user.

So, when you click on a view with a 75F point that isn't trended or linked in the station, that point isn't subscribed until you click on it. The next time the site is polled (in the next minute, by default), it will appear on the list of subscribed points, and the latest value will be read from the API.

The short delay in loading is caused by the fact that a point isn't polled and read as soon as it's subscribed, which is what drivers that poll points individually do. The point has to wait for the next time the site is polled.

If points load faster when polled individually, why doesn't the 75F driver poll points individually?

The station wouldn't be able to keep up if we did it this way.

Even a tiny 75F site has a few hundred points, and these points all have to be fetched from the cloud, not a locally connected device. 

Reading in big batches is the only way that points can be updated once per minute without overtaxing the station.