BS407 [ETC]
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ETC 
THURLBY THANDAR INSTRUMENTS
BS407 Wide range precision micro-ohmmeter
RANGES AND ACCURACY
i
T
Accuracies apply over a temperature range of 18oC to 28oC 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.
BS407 PRECISION MILLI/MICRO OHMMETER
T
ZERO ADJUST
Charge
1µΩ to 20 kΩ
UNKNOWN
SENSE
Force on
Range
Resolu- Test Cur- F.S. Volt-
Accuracy
tion
1 µΩ
rent
250 mA
50 mA
10 mA
5 mA
age
µΩ
mΩ
Ω
kΩ
Set 20mV
Zero Clamp
Operate
Polarity
500 µV
1 mV
± 0.1% r ± 0.4% scale
± 0.1% r ± 0.2% scale
± 0.1% r ± 0.1% scale
± 0.1% r ± 0.1% scale
± 0.1% r ± 0.1% scale
± 0.1% r ± 0.1% scale
± 0.1% r ± 0.1% scale
± 0.1% r ± 0.2% scale
1999 µΩ
19.99 mΩ
199.9 mΩ 100 µΩ
1999 mΩ
19.99 Ω
199.9 Ω
1999 Ω
1999 19.99 199.9 1999 19.99 199.9 1999 19.99
Off
On
Ω
10 µΩ
_
+
µ
µ
50
µ
10 A
250mA 50mA 10mA 5mA 500µA 50
A
A
FORCE
2 mV
Force Current
10 mV
10 mV
10 mV
100 mV
200 mV
1 mΩ
10 mΩ
100 mΩ
1 Ω
500 µA
50 µA
50 µA
10 µA
● High basic accuracy of 0.1%
19.99 kΩ
10 Ω
●
Wide measurement range of 1 micro Ω to 20k Ω
FACILITIES
20mV Clamp
●
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
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 2000Ω and 20kΩ 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.
● Switchable 20mV clamp for ‘dry circuit’ testing
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.
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
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.
18 mV ± 2mV with 20mV Clamp Active
< 6V with 20mV Clamp Inactive
> 1V (> 0.5V on 1999µΩ range).
Compliance
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.
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
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.
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 (1999µΩ range). Low battery indica-
tion in display.
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.
AC Line
Wide measurement range
Built-in battery charger allows instrument operation while re-charging.
Nominal re-charge time 16 hours.
GENERAL
The BS407 has eight push-button selected decade measurement
ranges from 1.999mΩ up to 19.99kΩ.
This unusually wide range makes it suitable for a greater variety of appli-
cations than other micro-ohmmeters.
Display:
Casing:
Power:
3.5 digit LCD with 12.5mm characters.
ABS casing with metal tilt stand giving 15o angle.
230V or 115V ±14% 50/60Hz, adjustable internally;
20VA max. Installation Category II.
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.
Operating Range: +5oC to + 40oC, 20% to 80% RH.
Storage Range:
Environmental:
High resolution and accuracy
Withalowestrangeof1999µΩtheBS407canresolveonemicro-ohm.
-10oC to +65oC
Indoor use at altitudes to 2000m, Pollution Degree 2.
Precision analogue circuitry ensures a high measurement accuracy of
up to 0.1% of reading ± 1 digit.
Electrical Safety: Complies with EN61010-1.
EMC:
Size:
Complies with EN61326.
220(W) x 82(H) x 230(D) mm, (10.3 x 3.4 x 9.2")
excluding feet and tilt stand.
1.3 kg (3lb).
Designed and built in the EEC by:
Weight:
ACCESSORIES
SUPPLIED
Kelvin Test Clip Leads, Operating Manual, IEC Mains Lead
OPTIONAL
Carrying Case
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
Thurlby Thandar Instruments Ltd. operates a policy of continuous development
and reserves the right to alter specifications without prior notice.
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