Just how much data can a SIXNET IPm-based DCS controller or RTU store? Use the steps below to calculate each datalog file size and the length of time you can store data in battery-backed memory or FLASH memory before the oldest data is overwritten. If multiple datalog files will be loaded into your controller or RTU, perform the calculation for each datalog file and add the results together to determine the total memory usage.

STEP 1 - Observe the total number of bytes per datalog record: When you create a datalog configuration you will use the Record Content window to choose the I/O to be logged. The Record Content window includes a display of the total number of bytes each record will consume, based on the I/O you have chosen to log.

STEP 2 - Calculate the number of datalog records stored per day: When you create a datalog configuration you will use the Capture Parameters window to define the rate at which I/O will be logged. Calculate the number of records logged per day, based on the logging rate you specify. 
Example: 1440 mins. per day ÷10 minute (logging rate) = 144 datalog records per day.

STEP 3 – Calculate the total number of bytes per day: Multiply the number of records per day by the total bytes per record. Then add approximately 10 percent overhead for tag names, file header etc. (See "Viewing Maximum Datalogging Memory Usage" below if you wish to see the exact amount of datalogging memory used in the station.) 
Example: 144 records x 54 bytes per record x 1.10 (10%) = 8554 total bytes per day.

STEP 4 - Calculate how many days you can log data before reaching a given file size: Divide file size* by bytes per day. 
Example: 400,000 bytes ÷ 8554 bytes per day @ 46.75 days. 

Is this enough data storage? 
Sixlog datalogging is just a front end buffer for your Windows software. You only need to store data in the IPm-based controller until it is transferred to the hard disk in your computer. 

Viewing Maximum Datalogging Memory Usage: 
The IPm file system uses file compression. Each datalog file will be small when it is first loaded and will increase in size as data is logged. The Resource Allocation Window (accessed from the configuration window for the controller) displays the amount of compressed nvram (battery-backed) usage. To view the worst case (maximum) nvram usage for the Datalog files and all other battery-backed files currently loaded into the controller or RTU, open the File Operations window for that controller / RTU. Browse to the /nvram folder and add up the file sizes for all files in the /nvram folder and subfolders (if any). If you are datalogging to FLASH memory, browse to the /home/datalog folder and add the file sizes for all files in that folder. The File Operations window displays the uncompressed file sizes, so the total of the individual file sizes will be an accurate representation of maximum nvram usage. 

Datalogging in FLASH Memory to Increase Capacity: 
IPm-based controllers and RTUs now have the ability to store datalog records in their FLASH file system memory. Most newer units have 16 megabytes of FLASH, of which approximately six megabytes are available to hold datalog records and user applications. The Resource Allocation Window (accessed from the configuration window for the controller) will display the compressed file system memory usage, including the amount of available free memory in your controller. In the example below, 9329 Kbytes are available. Because the file system is compressed, it is recommended that no more than six megabytes be used for datalogging and user applications.

Data can be logged at a rate as fast as one second when FLASH memory is used for the data storage. Please note that storing datalog records in FLASH memory requires version 3.0 or newer IPm firmware and version 2.9 or newer of the SIXNET I/O Tool Kit. The latest version of firmware and software are available for download from redlion.net. 

Configuring an IPm-based Controller to Transmit its Datalog Records (client transfer): 
IPm-based controllers and RTUs can be configured to function in a "client" mode, where the controller or RTU will send its Datalog records to a computer running the Sixlog Server or Citect Datalog Server. These servers look for "client" messages sent from SIXNET IPm-based controllers / RTUs and will write the data to file(s) on your computer’s hard drive or Citect trend history files as configured. This capability minimizes the amount of battery-backed memory needed for datalogging and also provides a way to send information to a computer upon an alarm condition. It is also useful in situations where it is desirable to minimize communication between the I/O and the computer.

Disclaimer

It is the customer's responsibility to review the advice provided herein and its applicability to the system. Red Lion makes no representation about specific knowledge of the customer's system or the specific performance of the system. Red Lion is not responsible for any damage to equipment or connected systems. The use of this document is at your own risk. Red Lion standard product warranty applies.

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