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Product category: Stand-Alone Instruments
News Release from: TTi (Thurlby Thandar Instruments) | Subject: BS407
Edited by the Electronicstalk Editorial Team on 12 August 2004

Micro-ohmmeter resolves down to a
micro-ohm

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The BS407 is a precision ohmmeter with resistance ranges from 2mohm to 20kohm and with an accuracy of 0.1%.

The BS407 is a precision ohmmeter with resistance ranges from 2mohm to 20kohm and with an accuracy of 0.1% The resolution on the lowest range is 1uohm

Most digital multimeters offer a best resolution which is at least 1000 times poorer than that of the BS407.

A very high-resolution multimeter may attempt to resolve fairly low resistances, but it does so by resolving extremely low voltages (typically 1nV/uohm), 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 nickel-metal hydride (NiMH) rechargeable batteries.

The battery charger is built into the instrument, and charging can take place during operation.

The instrument uses a four-terminal measurement system with high-quality Kelvin clip leads.

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 to prevent spurious results from being recorded.

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.

The BS407 measures 220 x 82 x 230mm and weighs 1.3kg.

It costs GBP 495 (plus VAT) in the UK.

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