The 238 Source-Measure Unit (SMU) is a fully programmable instrument, capable of sourcing and measuring voltage or current simultaneously. This system is really four instruments in one; voltage source, voltage measure, current source, and current measure. 

Applications:
These instruments address a wide variety of applications, including the characterization of semiconductor devices and the measurement of leakage currents or insulation resistance. They are particularly useful as source and measuring instruments in automated test equipment (ATE).
 
Specifications:
    SOURCE-MEASURE UNIT: Sources voltage while measuring current, or sources current while measuring voltage.
    FUNCTION: Can be used as DC source or meter, sweep source, or full source-measure unit.
    SOURCE-DELAY-MEASURE CYCLE: Default Delay: Fixed delay for instrument settling. User Delay: Additional delay for device under test or system capacitance.
    MEASURE: Integration Time Fast: 416 µs 4-digit resolution Medium: 4 ms 5-digit resolution Line Cycle: 16.67 ms (60 Hz) or 20.00 ms (50 Hz), 5-digit resolution Elapsed Time: Measures and stores time from sweep trigger to measurement complete for each step of sweep.
    RANGING: Source: Auto-ranging through keypad entry; fixed range selection using rotary dial and SELECT keys (DC function). Fully programmable in SWEEP function. Measure: Auto or fixed range. Fixed range selection made by choice of COMPLIANCE value.
    FILTER: Takes n measurements, calculates and outputs average (n = 2, 4, 8, 16, or 32, selectable).
    SUPPRESS:Subtracts displayed measurement from subsequent readings.
    MENU: DC Measurement Delay, Default Delay On/Off, Local/Remote Sense, 50/60Hz, IEEE Address, Self Tests.
    DATA ENTRY: Numeric keypad or detented rotary dial.
    TRIGGER: Input and Output: Set for any phase of SOURCE-DELAY-MEASURE sequence or trigger output at end of sweep. Origin: Internal, External (including front panel MANUAL TRIGGER button), IEEE-488 bus (TALK, GET, "X").
    MEMORY: Stores one full sweep (up to 1000 points) of source, delay, and measure values, elapsed times, and sweep parameters. Lithium battery backup.
    INTERLOCK: Use with test fixture or external switch. Normally closed; open puts instrument in standby.