A resolution at least a thousand times better than a digital multimeter, in a fully portable, rechargeable instrument which generates enough test voltage to reduce thermal EMF effects
The BS407, new from TTi (Thurlby Thandar Instruments), is a precision ohmmeter with resistance ranges from 2 milliohms up to 20 kilohms and an accuracy of 0.1%.
The resolution on the lowest range is one micro-ohm.
Most digital multimeters offer a best resolution which is at least 1000 times 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 1nV 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 is a fully portable instrument which operates from internal NiMH rechargeable batteries.
The battery charger is built into the instrument, and charging can take place during operation.
The BS407 uses a four-terminal measurement system via a high-quality Kelvin clip lead.
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.
A front-panel operated 'clamp' switch is available to limit the maximum voltage across the unknown resistance to 20mV.
This is a requirement for the measurement of switch contact resistances to international standards.
The BS407 measures 220 x 82 x 230 mm and weighs 1.3 kg.
It costs £495 (plus VAT) in the UK.
