Can two Model 2651A be connected in parallel or series?

A Keithley Model 2651A SourceMeter® Instrument can be connected in both series and parallel with another (and only one other) instrument of the same model number for higher voltages and currents as long as certain important conditions are observed. See page 2-48 of the 2651A Reference Manual, "Combining SMU outputs", for details of configuring and connecting SMUs for parallel and series operation.

When combining the outputs of two 2651A instruments, restrict operation to pulse only for all operating areas (both the standard and the extended operating areas).

Placing two voltage sources in parallel, or two current sources in series, is not recommended.

Source current using parallel SMUs

This configuration allows a maximum pulse level of up to 100 A with 36 V compliance. 

Source voltage using series SMUs

This configuration allows a maximum pulse level of up to 80 V with 45 A compliance.

Source voltage with extended current using parallel SMUs

This configuration allows a maximum pulse level of up to 36 V with 95 A compliance. 

For information on combining Keithley 2657A instruments, see this FAQ.