Model 121 programmable DC current source

Model 121 features

  • 7 decades of output current, selectable in 13 steps
  • Programmable current output, 100 nA to 100 mA
  • Low-noise output
  • Large 3-digit LED display
  • Simple user interface
  • Current reversal feature
  • USB interface enables integration with automated test systems
  • DIN panel-mountable package
  • Detachable output terminal block
  • CE mark certification
Download the latest instrument firmware


The Model 121 programmable DC current source is a precision instrument suitable for bench-top use or panel-mounted operation in labs, test facilities, and manufacturing environments. It provides a low-noise, highly stable source of current up to 100 mA, with convenient manual selection through 13 pre-set output levels, each representing a ten-fold change in power when attached to a resistive load. A “user” setting allows the current output to be defined anywhere within the unit's operating range, from 100 nA to 100 mA.

Programmable operation is also possible via the instrument’s USB computer interface, through which the Model 121 can be commanded to output any desired current at any time. Thus, application-specific test currents can be driven from an external PC.

The instrument operates at 5 VDC, and power is supplied by the external AC wall-mount supply provided with the standard Model 121. The supply will automatically conform to any AC line voltage ranging from 100 VAC to 240 VAC, 50 or 60 Hz.

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The Model 121 current source is ideally suited for testing, measuring, and operating resistive and semiconductor devices, such as:

  • Lake Shore Cernox™ temperature sensors
  • Other resistance temperature detectors (RTDs) such as platinum sensors
  • Diode temperature sensors, including Lake Shore DT-670s
  • LED devices
  • Hall sensors used for magnetic field measurement

An accurate, stable source of current is key to ensuring consistent operation of these devices, where the voltage drop across the device can be dependent upon temperature, magnetic field, and other parameters. The instrument’s wide output range is of great value when used with RTD-type sensors whose resistance can vary with temperature by as much as 6 orders of magnitude. The current reversal feature enables compensation for thermal EMF, which is important for accurately measuring resistors at very low excitation levels.

Example applications include:

  • Basic device QC (“good/bad” verification)
  • LED brightness testing (constant device current)
  • Temperature sensor calibration (determine resistance at fixed calibration points)
  • Temperature measurement (using a voltmeter readout)
  • Magnetic sensor calibration and measurement
  • Semiconductor device measurements
  • Circuit prototyping (fixed current source)
  • Small-scale electrochemical applications

Whether operating over a wide range of environmental conditions, establishing precise sensor calibrations, or simply testing devices for conformance, the Model 121 provides a convenient and reliable alternative to simple voltage-based circuits and a very affordable alternative to more expensive multi-function current sources. It can be readily integrated into automated test systems using its built-in USB computer interface and offers a highly readable, simple-to-use operator display.