Keithley 2601B Reference Manual page 237

Series 2600B System SourceMeter® Instrument Reference Manual Section 4: Theory of operation
The current compliance limit applies both to positive and negative currents. For example, if you set
the current compliance limit to 50 mA, the current limit applies to ±50 mA.
For this example, the Series 2600B is programmed to source 2 V and to limit current to 50 mA. When
the SMU turns on, the battery voltage is higher than the programmed voltage source value. Since the
SMU is unable to deliver the programmed voltage, the SMU is placed in current compliance and
begins to sink current. Sink operation continues until the battery voltage equals the programmed
voltage source level and the current in the circuit drops to nearly 0 A.
In the following figure, as the battery drains, the battery voltage is lowered (shown by the green arrow
in the figure). Operation will continue in this direction until the SMU is able to deliver the programmed
voltage source value.
Since the battery is a power source, initial operation can occur anywhere along the initial battery
voltage line. This voltage is only limited by the capability of the battery (see the following figure).
Figure 97: Considerations when sourcing voltage and sinking power
2600BS-901-01 Rev. B / May 2013 4-11