In this video you will see how to use SIEMENS SIMATIC CFC trend view for limited data logging for engineering purposes.
There are some possibilities to log internal S7 variables:
1-Tag archiving capability of WINCC
2-Autem PLC analyzer
http://autem.de/index.php?site=en_home
3-ibaPDA-S7-Analyzer
http://www.iba-ag.com/
SIEMENS Forum discussions:
https://support.industry.siemens.com/...
Data logging | S7-400 | cycle precise data logging | trend | tag logging | data logging