Showing Results for Keithley 238

The Model 238 is a high current source-measure unit. It sources voltage while measuring current, or sources current while measuring voltage. When programmed to source voltage, the Imeter of the 238 is connected in series with the Vsource and output. When programmed to source current the Vmeter is connected in parallel to the Isource and output.

The source measure unit can also be used as a stand-alone voltmeter or current meter, a DC source, or sweep source.

The 238 can be programmed to perform source-measurements as a function of a stepped voltage or current. Voltage and current can be swept linearly, logarithmically, or pulsed. The START, STOP, STEP method of setting sweep parameters may be appended to obtain more complex test sequences.

Creating custom sweeps of voltage or current is facilitated by the use of three waveform operations: CREATE, APPEND, and MODIFY. These allow the user to select waveform parameters, combine multiple waveforms, and select and change any points in a waveform previously created or appended.

The 238 outputs and inputs are fully guarded, and the units are configured to allow four-terminal measurements. Two-terminal measurements are also available for more standard test procedures. These outputs can be floated up to ±200V from ground.

• Vsource: The 238 can source from ±100 µV to ±110 V. The programmable current compliance is up to 1 A, except for 100 mA on the 110 V range
• Isource: The 238 can source from ±100 fA to ±100 mA (like Models 236 and 237), and has an additional source range of ±1 A. The programmable voltage compliance is up to 110 V, except for 15 V on the 1 A source range
• Vmeter: The 238 can measure from ±10 µV to ±110 V, except for 15 V on the 1 A range
• Imeter: The 238 can measure from ±10 fA to ±1 A, except for 100 mA on the 110 V source range
• Voltage
  • Noise (p-p typical) at 0.1 - 10 Hz: 110 V is <3 ppm or range, 15 V is <3 ppm of range, 1.5 V is <10 ppm of range
  • Wideband noise: 0.1 to 20 MHz, 8 mV p-p typical
  • Overshoot: <0.01% (110 V step, 10 mA range)
  • Settling time: <500 μs to 0.01% (110 V step, 10 mA range)
  • NMRR: >60 dB at 50 or 60 Hz (LINE CYCLE integration time selected)
  • CMRR: >120 dB at DC, 50 or 60 Hz (LINE CYCLE integration time selected)
  • Input impedance (as a voltmeter): >10¹⁴ Ω paralleled by <20 pF
• Current
  • Noise (p-p of range): 0.1–10 Hz: <3 ppm (<20 ppm on 1 nA, 10 nA and 1 A ranges)
  • Overshoot: <0.01% typical (10 mA step, R_L = 10 kΩ)
  • Settling time: <500 µs to 0.01% (10 mA step, R_L = 10kΩ)
  • Output R, C: >10¹⁴ Ω paralleled by <20 pF (on 1 nA range) 
• Sweep waveforms
  • Fixed Level: LEVEL, COUNT (number of DELAY-MEASURE cycles), DELAY, BIAS
  • Linear Stair: START, STOP, STEP, DELAY, BIAS
  • Logarithmic Stair: START, STOP, POINTS/DECADE (5, 10, 25, or 50), DELAY, BIAS
  • Pulse: LEVEL, COUNT, T_ON, T_OFF, BIAS
  • Linear Stair Pulse: START, STOP, STEP, T_ON, T_OFF, BIAS
  • Logarithmic Stair Pulse: START, STOP, POINTS/DECADE (5, 10, 25, or 50), T_ON, T_OFF, BIAS
• Waveform operators
  • Create: Allows selection of waveform parameters. Generates all source values
  • Append: Combines multiple waveforms and adds new points to those already in memory
  • Modify: Select and change any points in a previously created or appended waveform
• Minimum source-delay-measure cycle time: 1 ms
• Response to IEEE-488 command (as a source): 25 ms
• Measurement rate: 1 ms per point into internal buffer
• Continuous measurement speed (source DC value over IEEE-488 bus): 110 readings per second
• Trigger latency time: <2 ms
• Load capacitance: Stable into 20,000 pF typical
• Remote sense: Corrects for up to 2 V drop in each output lead. Maximum 1 kΩ per sense lead for rated accuracy. Residual output resistance (as a voltage source) is 0.5 Ω
• Guard
  • Output Resistance: ≤12 kΩ
  • Maximum Output Current: ±2 mA
  • Open Circuit Offset Relative to Output HI: ±2 mV maximum
• Maximum common mode voltage: 200 Vpeak