Whether using a simple multimeter or a high-precision micro-ohmmeter, choosing the right measurement method is crucial for reliable results. Measuring electrical resistance is one of the fundamental tasks in electrical engineering. While simple measurement methods are sufficient in the higher ohm range, precise measurements in the micro- or milliohm range place special demands on the technology used. Here, the choice of measurement method determines accuracy and reliability.
While a digital multimeter usually use the 2-wire method, professional measurement systems such as the PROMET product family rely on the precise 4-wire or Kelvin method.
In the 2-wire measurement method, the resistance is determined by the test object via two wires. Both the test current and the measurement signal flow through the same wires. The wire and contact resistance of the measuring wires are therefore directly included in the measurement result.
The 2-wire measurement with a multimeter is suitable for measuring high resistances in the kΩ to MΩ range, but shows significant measurement errors at low resistances (below a few Ω), as the influence of the connecting wires can be comparatively large.
The 4-wire or Kelvin measurement method separates the current supply and voltage measurement. Two wires carry the constant test current through the test object, while two separate wires measure the voltage drop directly at the test object. This eliminates the resistance of the measuring/supply lines and the contact transitions, so that no additional measurement error occurs.
The 4-wire measurement thus enables very precise measurements down to the milli- and microohm range by eliminating line and contact resistance, but requires special measurement technology.
→ The process was named after physicist William Thomson, “Lord Kelvin,” who developed this method back in 1876.
The resistance measurement systems in the PROMET series from KoCoS are designed for precise 4-wire measurement. They deliver high currents up to 600 A, enabling even very small contact resistances to be determined accurately under practical conditions.
The advantages:
While the two-wire method with a multimeter is sufficient for standard measurements at higher resistances, the Kelvin measurement method enables high-precision measurements in the low-ohm range. With the PROMET resistance measurement systems, KoCoS provides powerful tools that combine accuracy, practicality, and user-friendliness. This is a decisive factor for reliable testing in development, production, and maintenance.
