HP 34401A - 6 1/2-Digit Bench Multimeter

HP 34401A — 6½‑Digit Bench Multimeter

High‑Accuracy • True RMS • DC/AC Voltage & Current • Resistance • Frequency • Continuity

Purpose & Capabilities

A precision laboratory‑grade digital multimeter designed for:

• High‑accuracy voltage and current measurement

• Calibration‑quality readings

• Sensitive analog circuit work

• Power supply and battery characterization

• Frequency and duty‑cycle measurement

• General electronics troubleshooting

The HP 34401A is renowned for excellent accuracy, low noise, fast measurement speed, and rock‑solid stability.

Access Level

• General Member Use

• No reservation required

• Handle with care — this is a precision instrument

• Only authorized volunteers may open or calibrate the unit

Specifications

Measurement Capabilities

• DC Voltage:

  • Ranges up to 1000 V

  • Accuracy down to the microvolt level

• AC Voltage:

  • True RMS

  • Up to 750 V

• DC Current:

  • Up to 3 A

• AC Current:

  • True RMS

  • Up to 3 A

• Resistance:

  • 2‑wire and 4‑wire (Kelvin)

  • Up to 100 MΩ

• Frequency:

  • Up to ~300 kHz

• Continuity & Diode Test:

  • Audible continuity

  • Diode forward‑voltage measurement

Performance

• Resolution:
  6½ digits

• Input Impedance:

  • 10 MΩ (DC)

  • High‑impedance modes available

• Display:
  VFD with dual‑display capability

• Interfaces:
  GPIB + RS‑232

• Sampling / Speed:
  Fast measurement modes for data logging

Before You Begin

• Inspect the meter:

  • Ensure leads are in good condition

  • Verify correct jack placement (especially for current)

  • Check that the meter is set to the correct mode

• Use proper leads:

  • CAT‑rated leads for high‑voltage work

  • 4‑wire Kelvin leads for precision resistance

• Confirm your circuit is safe to probe:

  • No high‑energy inductive loads

  • No mains AC unless you are trained

Operating Guidelines

Voltage Measurement

• Select DCV or ACV

• Use appropriate range or auto‑range

• For sensitive circuits:

  • Use high‑impedance mode

  • Avoid loading the circuit

Current Measurement

• Move lead to current jack

• Select DCI or ACI

• Break the circuit and insert meter in series

• Never measure current in voltage mode

Resistance Measurement

• Select Ω

• For precision:

  • Use 4‑wire mode

  • Avoid touching leads during measurement

  • Ensure circuit is unpowered

Frequency Measurement

• Select Freq

• Works best with clean sine or square waves

• Useful for oscillator verification

Continuity / Diode

• Audible beep for continuity

• Diode mode shows forward voltage drop

Supported Use Cases

Approved:

• Precision voltage and current measurement

• Power supply testing

• Battery characterization

• Analog circuit debugging

• Oscillator frequency checks

• Resistance measurement (2‑wire or 4‑wire)

• General electronics troubleshooting

Not approved:

• Mains AC probing without training

• High‑energy inductive loads

• Measuring current above 3 A

• Using non‑CAT‑rated leads for high voltage

• Any measurement requiring isolation or differential probes

Care & Etiquette

• Always return leads to the correct jacks

• Do not yank banana plugs

• Keep the meter clean and dry

• Avoid dropping or bumping the unit

• Report:

  • Flickering display

  • Unstable readings

  • Burnt smell

  • Loose jacks or damaged leads

Common Issues & Troubleshooting

• Incorrect readings

  • Wrong mode or range

  • Leads in wrong jacks

• No continuity beep

  • Dirty leads or oxidized contacts

• Resistance reads too high

  • Circuit not fully isolated

  • Poor lead contact

• AC readings unstable

  • Noisy or distorted waveform

• Meter overload

  • Voltage or current exceeds range