TTi (Thurlby Thandar Instruments) has improved its BS407 micro-ohmmeter by increasing its accuracy at the lowest values of resistance.
The BS407 can resolve resistance down to 1 microhm, and has ranges with full scales from 2 milliohms up to 20 kilohms with a basic accuracy of 0.1%. It uses a 4-terminal measurement system via high quality Kelvin clip leads, and has a maximum excitation current of 250 mA. Current reversal can be selected to identify errors from thermal EMF.
A front-panel operated ‘clamp' switch limits the maximum voltage across the unknown to 20 mV. This is a requirement for the measurement of switch contact resistances to international standards. Further front-panel switches allow for current reversal and for current diversion. The latter enables in-situ zero adjustments to be made.
The BS407 operates from built-in NiMh rechargeable batteries. Battery operation eliminates the noise that can be created by ground loops on AC line powered equipment. The instrument is fully portable, and has its own battery charger built in.
The instrument is lightweight and compact, measuring 220 x 82 x 230 mm and weighing 1.3 kg. The price in the UK is £515 (plus VAT).