BS407 - Precision Micro Ohmmeter

  High basic accuracy of 0.1%
  Wide range of 1? Ohm to 20k Ohm
  Current reversal switch for detecting thermal emf effects
  Current diversion switch for easy zero-ing
  Four terminal measurement using Kelvin clip leads
  Battery operation with built-in charger
  20mV clamp for ?dry circuit? testing

A dedicated but versatile instrument

The BS407 is an instrument which is fully optimised for the task of accurate measurement of low resistances with a best resolution of 1?Ohm.
Most multimeters offer a best resolution which 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.

Rapid 4-terminal measurement

The BS407 uses a four terminal measurent 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.

Battery operation with built-in charger

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.

Wide measurement range

The BS407 has eight push-button selected decade measurement ranges from 1.999mOhms up to 19.99kOhms. 
This unusually wide range makes it suitable for a greater variety of applications than other micro-ohmmeters.
A front panel operated ?clamp? switch is available to limit the maximum voltage across the unknown to 20mV. This is a requirement for the measurement of switch contact resistances to international standards.

High resolution and accuracy

With a lowest range of 1999?Ohms the BS407 can resolve one micro-ohm.
Precision analogue circuitry ensures a high measurement accuracy of up to 0.1% of reading ? 1 digit.