The UT61C sends 14 byte packets and several websites have the protocol. The protocol is in the file UT61BCD.LOG on this site.
http://www-user.tu-chemnitz.de/~heha/hs_freeware/UNI-T/
Here is the meter chip datasheet 富晶，類比晶片的首選.
Making an interface cable is a bit tricky. These meters have opto-isolators and use tricks to generate RS232 with power from control lines driven by the PC serial interface.
I was able to use 5V and a resistor to generate TTL serial from the output of the opto-isolator.
I don't know how the UT61C does it's serial.