CT as an acronym is really non specific can be used to describe a Current Transformer or Current Transducer depending on how nit picky a person might be
and here a simple circuit for measuring higher voltage DC with an analog optic coupler
using either HCNR200 ( with voltage divider) or IL300
http://forums.hackaday.com/viewtopic.php?f=4&t=3224
they are about a $1 if you buy in lots of 10
https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20170510120847&SearchText=HCNR200