Siemens S7-1500 Function Manual page 55

Memory usage and application examples
3.2 Memory usage for data logging
Header
Header bytes of the data log = header character bytes + 2 bytes
Header character bytes
● No data header and no time stamp = 7 bytes
● No data header and time stamp (with time stamp header) = 21 bytes
● Data header and no time stamp = Number of character bytes in all column headers
including separating commas
● Data header and time stamp (with time stamp header) = Number of character bytes in all
column headers including separating commas + 21 bytes
Data
Data bytes of the data log = ((data bytes in a data record + time stamp
bytes + 12 bytes) * number of data records)
Data bytes in a data record
The DATA parameter of the "DataLogCreate" instruction points to a structure. The structure
assigns the number of data fields and the data type of each data field for a data log data
record.
Multiply the number of the respective data type with the number of bytes required for this
data type. Repeat this step for each data type in a data record. Add all the data bytes to
obtain the sum of all the data elements in a data record.
Size of the individual data types
The data in data logs is saved as character bytes in csv format (comma separated values).
The table below shows the number of bytes that are required to save each data type.
Data type
Any
Bool
Byte
Char
Date
DInt
DTL
DWORD
Int
LDT
LReal
Real
Sint
54
Bytes
10
1
4
1
10
12
31
11
7
31
25
16
5
Structure and Use of the CPU Memory
Function Manual, 10/2018, A5E03461664-AC