a dedicated but versatile instrument the BS407 is an instrument which is fully optimised for the task of accu - rate measurement of low resistances with a best resolution of 1 ? . most multimeters offer a best resolution which is at least one thousand poorer than this. a very high resolution multimeter may attempt to re- solve fairly low resistances, but it does so by resolving extremely low volt- ages (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 un- known 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 kel - vin 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 re - chargeable 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 1.999m ? up to 19.99k ? . this unusually wide range makes it suitable for a greater variety of appli - cations 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 mea - surement of switch contact resistances to international standards. high resolution and accuracy with a lowest range of 1999 ? the BS407 can resolve one micro-ohm. precision analogue circuitry ensures a high measurement accuracy of up to 0.1% of readin g 1 digit. ranges and accuracy accuracies apply over a temperature range of 18 o cto28 o c after a warm-up period of 30 minutes, and with the test connections in thermal equalibrium. specificied accuracy applies for a period of one year. range resolu - tion test cur - rent f.s. volt - age accuracy 1999 ? 1 ? 250 ma 500 v 0.1% r 0.4% scale 19.99 m ? 10 ? 50 ma 1 mv 0.1% r 0.2% scale 199.9 m ? 100 ? 10 ma 2 mv 0.1% r 0.1% scale 1999 m ? 1 m ? 5 ma 10 mv 0.1% r 0.1% scale 19.99 ? 10 m ? 500 a 10 mv 0.1% r 0.1% scale 199.9 ? 100 m ? 50 a 10 mv 0.1% r 0.1% scale 1999 ? 1 ? 50 a 100 mv 0.1% r 0.1% scale 19.99 k ? 10 ? 10 a 200 mv 0.1% r 0.2% scale facilities 20mv clamp operated by front panel switch. limits the open circuit voltage across the unknown to 20mv (+0mv, -4mv) for ?dry circuit? testing of switch and relay contacts. not available on the 2000 ? and 20k ? ranges. reverse polarity operated by front panel switch. reverses the polarity of the test cur - rent, enabling thermal emf effects to be detected and quantified. set zero operated by non-latching front panel switch and rotary offset control. diverts the test current way from the unknown allowing zero adjust- ment to be undertaken with the test leads in place. measurement source source emf 18 mv 2mv with 20mv clamp active < 6v with 20mv clamp inactive compliance > 1v (> 0.5v on 1999 ? range). compliance is the maximum voltage that can be tolerated from additional resistance in series with the force connections protection the instrument is protected against the back-emf of its own test current from any inductance. the instrument is protected against external voltage sources delivering up to one amp. protection against greater abuse is provided by non-flamable fusible resistors. power source battery four internal ni-mh cells (non removable). operating time depends upon the test current flowing - >150 hours with no test current, > 8 hours with maximum test current (1999 ? range). low battery indica - tion in display. ac line built-in battery charger allows instrument operation while re-charging. nominal re-charge time 16 hours. general display: 3.5 digit lcd with 12.5mm characters. casing: abs casing with metal tilt stand giving 15 o angle. power: 230v or 115v 14% 50/60hz, adjustable internally; 20va max. installation category ii. operating range: +5 o cto+40 o c, 20% to 80% rh. storage range: -10 o cto+65 o c environmental: indoor use at altitudes to 2000m, pollution degree 2. electrical safety: complies with en61010-1. emc: complies with en61326. size: 220(w) x 82(h) x 230(d) mm, (10.3 x 3.4 x 9.2") excluding feet and tilt stand. weight: 1.3 kg (3lb). accessories supplied kelvin test clip leads, operating manual, iec mains lead optional carrying case BS407 wide range precision micro-ohmmeter thurlby thandar instruments ltd. operates a policy of continuous development and reserves the right to alter specifications without prior notice. designed and built in the eec by: thurlby thandar instruments ltd . glebe road, huntingdon. cambs. pe29 7dr united kingdom tel: +44 (0)1480 412451 fax: +44 (0)1480 450409 e-mail: sales@ tti-test.com web: http://www. tti-test.com high basic accuracy of 0.1% wide measurement range of 1 micro ? to 20k ? current reversal switch for detecting thermal emf effects current diversion switch for easy zero setting four terminal measurement using kelvin clip leads battery operation with built-in charger switchable 20mv clamp for ?dry circuit? testing thurlby thandar instruments 50 ? zero adjust sense force unknown t i t BS407 precision milli/micro ohmmeter 19.99 199.9 1999 operate set 250ma 50ma 10ma 5ma polarity zero clamp 1999 1999 19.99 19.99 199.9 + _ charge force on force current 20mv 500 a 50 a 50 a 10 a off on to 20 k ? 1 ? ? ? m ?? k ? ?
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