The BS407 is a dedicated instrument for accurate measurement of low resistances, with a best resolution of 1 µΩ. Most multimeters offer a best resolution that is at least one thousand poorer than this. A very high resolution multimeter may attempt to resolve fairly low resistances, but it does so by resolving extremely low voltages (typically one nano-volt per micro-ohm), making it subject to severe errors from thermal emf effects and noise. In contrast, the BS407 generates sufficient test voltage across the unknown resistance to combat noise and reduce thermal emf effects to manageable levels. Current reversal can then be used to eliminate any remaining thermal offset. The BS407 uses a four terminal measurement system via high quality Kelvin Clip leads (supplied). For speed and convenience front panel switches are provided for current diversion (allowing in-situ zero adjustment) and current reversal (for identifying thermal emf errors). An LED indicator warns of open circuit leads thus preventing spurious results from being recorded. The BS407 is a fully portable instrument which operates from NiMh rechargeable batteries. The battery charger is built into the instrument and can be operated continuously during bench use. The BS407 has eight push-button selected decade measurement ranges from 1.999 mΩ up to 19.99 kΩ.
The BS407 is a wide‑range precision micro‑ohmmeter designed for accurate low‑resistance measurements. It offers a measurement range from 1 µΩ to 20 kΩ, high basic accuracy of 0.1 % of reading + 1 digit, and a best resolution of 11 µΩ. Features include four‑terminal Kelvin clip leads, a 20 mV clamp for dry‑circuit testing, current reversal and diversion switches, and battery operation with a built‑in charger.
The instrument is powered by four internal Ni‑MH cells providing up to 150 hours of standby time, or by 230 V/115 V mains with a built‑in charger. It includes a 3.5‑digit LCD display, ABS casing with metal tilt stand, and complies with EN61010‑1 safety and EN61326 EMC standards. Supplied accessories are Kelvin test clip leads, an operating manual, and an IEC mains lead; a carrying case is optional.
| Measurement range | 1 µΩ to 20 kΩ |
|---|---|
| Accuracy | 0.1 % of reading + 1 digit |
| Resolution | 11 µΩ |
| Battery | Four internal Ni‑MH cells (non removable) |
| Power input | 230 V or 115 V, 20 VA max |
| Display | 3.5‑digit LCD, 12.5 mm characters |
| Size | 220 mm × 82 mm × 230 mm |
| Weight | 1.3 kg (3 lb) |
| Operating temperature range | +5 °C to +40 °C |
The BS407 measures resistances from 1 µΩ up to 20 kΩ.
It provides an accuracy of 0.1 % of reading plus 1 digit.
The battery can operate for more than 150 hours with no test current, and over 8 hours at maximum test current.
The instrument comes with Kelvin test clip leads, an operating manual, and an IEC mains lead; a carrying case is optional.