Look at your screen saver.
It say something like - lock screen after x time.

Thanks but I cannot find the setting for this. I was mistaken ,,,
it is not locking the screen but logging me off after ten minutes of non use and
I must continually log back on using my password.
Where do I go to disable this action or increase the time limit?

System > Preferences > Screen Saver
At the bottom it says: Lock screen when screensaver is active.
If this is checked, remove it.