Time Machine Keeps Disconnecting

[galaxy7]

So I have an external hard drive labeled and using as a TimeMachine hooked up to my new imac. But it looks like when the computer is either going to sleep or the screen saver kicks in, it's disconnecting the TimeMachine. When I come back to my computer, The drive no longer shows up in the Finder, and I get the notification (in the upper right screen) that TimeMachine was not ejected properly, and to make sure I eject it before removing.

I cannot find in setting where/how to address this. Any tips? Thanks everyone.

 

[galaxy7]

Well, in Energy Saver, I unchecked "put hard disk to sleep when possible", and this seems to have worked. Don't know if that affects anything else major or not, but....