Relay board with RGND... what is RGND?

hello. 

i bought few inexpensive single relay boards.  i'm used boards having vcc, gnd, , pins energize each relay.  board has additional pin, rgnd.  rgnd , when should using it?

thanks insight!
dan

i suspect gnd connection arduino in conjunction ch1 , rgnd connection coil power supply in conjunction vcc.

but don't blame me if smoke escapes.

...r

Arduino Forum > Using Arduino > Motors, Mechanics, and Power (Moderator: fabioc84) > Relay board with RGND... what is RGND?

arduino