Archiving Trend View Data

[franji1]

So storage is based on the MB set by the user? Where is this in the manual (topic number)? I was reading through the trend view information in the help files and apparently missed the memory allocation settings discussion.

A couple places
DMD0291 Trend View Display Options
This topic covers both the configuration of a specific trend point in a specific Trend View, along with the Global Options for All New Trend Views

For a specific Trend View trend point's Data size, see the Historical Data Group setting

There is also a section below this that discusses the general settings for all New Trend Views (Global Options for All Trend Views)
In that section, look for the Historical Data section.  This is the default data collection size for all new Trend View elements

Note that this is the size of the data, which is logged when a change in value occurs.  That means that values that change frequently will fill up the allotted size quicker than something that changes less frequently.  Hence values that change a lot will have data "roll off the end" (actually roll off "the beginning") more frequently.

[RBPLC]

Couple of Questions:

1) The help file says there is a "10 Mb per data point" limit on storage space. The "Historical Data" selection section allows you to set values larger than 10 MB? Why does the "Historical Data" section allow you to set a value larger than 10 MB?

2) In the "Export/Logging Method" section, let's say that I set the "Log values for all elements on a specified timer interval" to 1s. When I go to export a trend, I get an "Export Options" dialog window. In this window is the another "Export/Logging Method" section where I have the ability to again set a log time. What happens if during export I choose a value of 10 ms when I had previously set this value at 1s?

[franji1]

Couple of Questions:

1) The help file says there is a "10 Mb per data point" limit on storage space. The "Historical Data" selection section allows you to set values larger than 10 MB? Why does the "Historical Data" section allow you to set a value larger than 10 MB?

That was an old limit back around Rel 2.0.  The limit is now 100 MBytes for everything.

2) In the "Export/Logging Method" section, let's say that I set the "Log values for all elements on a specified timer interval" to 1s. When I go to export a trend, I get an "Export Options" dialog window. In this window is the another "Export/Logging Method" section where I have the ability to again set a log time. What happens if during export I choose a value of 10 ms when I had previously set this value at 1s?

Excellent question.

Realize that historical data in the View is different than logging to a disk file.  The 1/10/100 MByte limitations are for the Trend View Historical Trend.  That's how much data is allocated to that Trend View for that data point.

At any point in time, you can EXPORT that set of data in the Trend View to a file.  When you do that, you specify the frequency of the log entries, at a time interval, or all the data at whatever time the value changed.

HOWEVER, you can also just hit the RECORD button.  That starts writing the Trend View's data to a file IMMEDIATELY.  This file can get as big as it can get.  It is independent of the 1/10/100 MByte limits of the View.  Basically, all the data gets written to the log file as it is updated in the Trend View.  But since disk space is HUGE, it just keeps writing data (there is no need to truncate the data file).  Hence, when you hit the RECORD button, the Options for All Trend View is the rate at which the RECORD data gets written to the file.  You may have a twitchy analog signal, and 1 second sample rate is good enough, you can set that there, in case you are worried about exceeding the file limit (1 GigaByte is all Designer can import back in?)

Finally, when you actually go to SAVE the data to an actual USER NAMED FILE, Designer lets you specify the frequency of the data into THAT file.

So you could technically sample at a rate of 200ms (this is the rate written to the temporary file), but then save it at a rate of 1sec (this takes that temporary file and then rewrites the data at that rate to the user specified file name).

So, to simplify what I stated, the time interval in the All Trend View Options is the one used by the RECORD button.  When you go to actually SAVE the EXPORTED historical or the RECORDED data, that time interval goes through the current historical data set or the RECORDED data set and re-generates that data points at THAT interval.

[RBPLC]

I was trying to figure out practical limitations of logging/trending and it looks like the following is the case (please correct me where I'm wrong):

1) Under "Export/Logging Method", I was trying to figure out what a practical maximum practical sampling rate was. I see that if I set 0 for minutes and seconds I get a warning about setting the sampling interval to less than 100ms. I assume that 100ms is the maximum practical sampling rate that you guys would recommend?

2) When Exporting data from the trend view, it looks like the smallest time step that will export is 100ms, regardless if the "Export/Logging Method" time is set less than 100ms.

3) When specifying how much "Historical Data" to retain, you can enter more than 100 MB in this select box. It would probably be good to limit this entry box to the maximum 100 MB.

4) What would be the practical limit to the logging speed using the FILELOG command? I realize that this will depend on the number of data points logged and the type of data but for example what would be the fastest you could log 10 real elements? Is this more dependent on the scan speed of the controller than anything else?

I realize the BRX isn't a data logger and is not intended for high speed data acquisition, I'm just trying to determine some of its practical limits.

[franji1]

Just try it.  If it works on your PC with your PLC, and your communications, and your scan time, great.  If not, close some Trend Views.  Close any view with Status (or turn Status off for those views).  Or slow down sample rates.

But the UI will get S-L-O-W or even misbehave if you push the limits too far.