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 1µΩ.
Most multimeters offer a best resolution which is at least one thousand
poorer than this. A very high resolution multimeter may attempt to re-
solvefairlylowresistances,butitdoessobyresolvingextremelylowvolt-
ages(typicallyonenano-voltpermicro-ohm),makingitsubjecttosevere
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).
Forspeedandconveniencefrontpanelswitchesareprovidedforcurrent
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-
chargeablebatteries. The battery chargeris built into theinstrument and
can be operated continuously during bench use.
Wide measurement range
The BS407 has eight push-button selected decade measurement
ranges from 1.999mΩup to 19.99kΩ.
Thisunusuallywiderange 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
voltageacrosstheunknown to20mV. Thisisarequirement forthemea-
surement of switch contact resistances to international standards.
High resolution and accuracy
Withalowestrangeof1999µΩtheBS407canresolveonemicro-ohm.
Precision analogue circuitry ensures a high measurement accuracy of
up to 0.1% of reading ± 1 digit.
RANGES AND ACCURACY
Accuracies apply over a temperature range of 18oCto28
oC 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 µΩ1 µΩ250 mA 500 µV ± 0.1% r ± 0.4% scale
19.99 mΩ10 µΩ50 mA 1 mV ± 0.1% r ± 0.2% scale
199.9 mΩ100 µΩ10 mA 2 mV ± 0.1% r ± 0.1% scale
1999 mΩ1 mΩ5 mA 10 mV ± 0.1% r ± 0.1% scale
19.99 Ω10 mΩ500 µA 10 mV ± 0.1% r ± 0.1% scale
199.9 Ω100 mΩ50 µA 10 mV ± 0.1% r ± 0.1% scale
1999 Ω1Ω50 µA 100 mV ± 0.1% r ± 0.1% scale
19.99 kΩ10 Ω10 µA 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 2000Ωand 20kΩranges.
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 1999µΩrange).
Complianceisthe maximumvoltagethatcanbetoleratedfromadditional
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 (1999µΩrange). 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 15oangle.
Power: 230V or 115V ±14% 50/60Hz, adjustable internally;
20VA max. Installation Category II.
Operating Range: +5oCto+40
oC, 20% to 80% RH.
Storage Range: -10oCto+65
oC
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 Ωto 20k Ω
●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
50Ω
ZERO ADJUST
SENSE
FORCE
UNKNOWN
T
i
T
BS407 PRECISION MILLI/MICRO OHMMETER
19.99 199.91999
Operate Set
250mA 50mA 10mA 5mA
Polarity
Zero Clamp 1999 1999 19.9919.99 199.9
+_
Charge
Force on
Force Current
20mV
µµµµ
500 A 50 A 50 A 10 A
Off
On
to 20 kΩ1µΩµΩµΩ
mΩΩ
kΩ
µΩ
