101BExtended instructions
8.7 Data logging
S7-1200 Programmable controller
304
System Manual, 11/2011, A5E02486680-05
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
that give you access to data logs are stored in PLC firmware and do not use load
memory).
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
memory free space.
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)
Bool
2
Byte
5
Word
7
DWord
12
Char
4
String
257 (Fixed size): Regardless of number of actual text characters
The string text char automatic padding with blank characters = 254 bytes
Opening and closing double quote + comma characters = 3 bytes
254 + 3 = 257 bytes
USInt
5
UInt
7
UDInt
12
SInt
5
Int
7
DInt
12
Real
16
LReal
25
Time
15
DTL
24