Is there a limit to the amount of history you can keep on-line in PHD? We are supposed to keep 5 years and would like to do even more. Any disadvantages?
Some clients have as much as 18 years of on-line history. It really depends on the amount of data you have and how many files you have as well.
If you are talking about Honeywell PHD, with 32 bit PHD systems, you have a limitation of 1024 total files. Even with a 64 bit system, sometimes you will see problems if you have too many on-line files and the server or some interfaces (RDI’s) will take a long time to start up.
Other clients with large facilities of 100,000+ tags often try to limit on-line data to 5-6 years or so.
Older data can be “simplified” to, say, one data point per hour for many years of older data. This is done via Resampling. This feature, built into PHD before it was purchased by Honeywell, works very well and can be set up to run automatically and retroactively! I have experimented with this and can help you set it up if necessary.