Rigol MC3120 20 Channel Differential Multiplexer. Rigol MC3120 is a 20-channel multiplexer which is divided into two banks of 10 two-wire channels (HI and LO) each and can be used for 2-wire and 4-wire connections.
When making 4-wire resistance measurement, the instrument automatically pairs channel n with channel n+10. MC3120 is used with the external terminal block M3TB20 which has a built-in thermocouple reference junction.