Agilent/Keysight 428B

The Agilent/Keysight 428B is a clip-on DC milliammeter that performs non-intrusive current measurements by converting the magnetic field around a conductor into a proportional AC voltage, then processing and displaying it as DC current. No circuit interruption, soldering, or indirect calculations via voltage and resistance are required, eliminating loading errors and simplifying measurement workflows.

Technical Specifications

Measurement Range & Accuracy

• Current measurement: 0.02 mA to 10 A full-scale


• Accuracy: ±(3% of full scale + 0.15 mA)


• Complete DC isolation with no direct circuit contact Output Characteristics


• Front panel analog voltage output delivers 1 V into an open circuit at full-scale deflection


• Variable linear output with calibrated position: 0.73 ± 0.01 V into 1 kΩ


• Maximum 1.5 V into an open circuit in uncalibrated position


• Suitable for driving strip chart recorders Probe Specifications


• Probe inductance: Less than 0.5 µH


• Induced voltage: Less than 15 mV peak (worst case at 20 kHz and harmonics)


• Noise performance: 1 mA range < 15 mV rms across 1 kΩ; 3 mA range < 5 mV rms across 1 kΩ Frequency Response


• DC-only primary measurement capability


• Low-frequency AC currents up to 400 Hz measurable via oscilloscope or voltmeter connection to front panel output

Key Features

• Non-intrusive clip-on transducer design eliminates circuit disruption


• Magnetic field sensing converts DC current to proportional voltage signal


• Complete common mode rejection - responds only to target DC current


• Sensitivity enhancement available by passing multiple conductor loops through the probe


• Analog output suitable for external instrumentation and recording devices

Typical Applications Direct current measurement in electrical circuits where minimal circuit loading and non-invasive monitoring are required. Ideal for steady-state DC current characterization and long-term current trending via external recorders.

Compatibility & Integration Clip-on probe design accommodates various conductor sizes within physical envelope constraints. Analog front panel output integrates with oscilloscopes, voltmeters, and chart recorders.