24h data collecting in siemens s7

Hi,
Can someone tell me the principe how I can collecting data in my s7-cpu31x with using DBs and with my little experiences in PLC programming.
The application is a watertank with a level (4-20mA, precision not important).
I like to collect about 24houres and each 5 minutes the analog value and the time that it was registred. 1 Time a day I will call from an other scada software to this plc to 'empty' the DBs.
Need I to use 1 DB for the value and 1 DB for the 'time' it was registred ? Need it to be an automatique first-in, first-out.
If using 1 db with 255 words, can I use 1 byte for the time and 1 byte for the value.Maybe there is existing a free exemple program or principe.
Thanks, Jean

Is your data in interger or real.
Interger requires 2 bytes, real 4 bytes.
Time in hour, min, sec requires aleast 6 bytes.
Total about 10 bytes.
Data coolected over 24 hrs at 5 mins interval - 288
DB size - 2880 bytes
Since you collect data once a day, suggest alternating DBs everday
Best of Luck
Kiki
PLC programmer
oS2000
Singapore

If you are short with memory and you plan to sample it
periodically as you described, maybe there is no need
for timestamp in every record. Maybe just one timestamp
would do if the sampling interval is always the same.

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