Siemens SIMATIC S7 System Manual page 304

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8.7 Data logging

Determine the size of load memory free space

1. Establish an online connection between STEP 7 and the target S7-1200 PLC.

2. Download the program to which you want to add data log operations.

3. Create any optional user-defined web pages that you need. (The standard web pages

4. Use the Online and diagnostic tools to get the load memory size and percentage of free

5. Multiply the load memory size by the percentage that is free to obtain the current load

Maximum size rule for all data logs combined

The amount of load memory free space varies during normal operations as the operating

system uses and releases memory. You should limit the combined size of all data log files to

one half of the available free space.

Calculate the memory requirement for a single data log record

Log data is stored as character bytes in the CSV (comma separated values) file format. The

following table shows the number of bytes that are required to store each data type.

Table 8- 138 CSV file data sizes

Data type Number of bytes (data bytes plus separator comma byte)

that give you access to data logs are stored in PLC firmware and do not use load

load memory space (Page 640).

memory free space.

257 (Fixed size): Regardless of number of actual text characters

The string text characters + automatic padding with blank characters = 254 bytes

Opening and closing double quote + comma characters = 3 bytes

254 + 3 = 257 bytes

S7-1200 Programmable controller

System Manual, 11/2011, A5E02486680-05

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