BS407 Wide range precision micro-ohmmeter
Wide range precision micro-ohmmeter
High basic accuracy of 0.1%
Wide measurement range of 1µ W to 20k W
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
BS407 wide range precision micro-ohmmeter
A dedicated but versatile instrument
Rapid 4-terminal measurement
The BS407 is an instrument which is fully optimised for the task of
accurate measurement of low resistances with a best resolution of
It has applications beyond the testing of components such as measuring the resistance of motor or transformer windings, the properties of materials, the thickness of plates, the security of pipework
joints or wiring installations and many others.
It uses a Direct Current technique to measure true resistance,
rather than the resistive component of impedance which is shown
by AC excited RLC bridges. The test current for each range has
been carefully chosen to minimise heating of the sample under test
while being sufficient to minimise the effects of thermal emf and
This gives much greater accuracy at low resistances than can be
obtained from the very low test currents used by general purpose
high resolution multimeters. The low-noise low-drift bipolar amplifiers employed need much less noise filtering than alternative chopper stabilised technologies resulting in faster settling to the correct
The BS407 uses a four terminal measurement system via high
quality Kelvin 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 indicator lamp confirms correct flow of the measuring current
thus preventing spurious results from being recorded.
Battery operation with built-in charger
The BS407 is a fully portable instrument which operates from NiMh
rechargeable batteries. The battery charger is built into the instrument and can be operated continuously during bench use.
Accuracies apply for a one year period over a temperature range of 18 C to
28 C after a warm-up period of 5 minutes with the instrument and test cono
nections in thermal equilibrium. Tempco outside this range <±45ppm/ C
The BS407 has eight push-button selected decade measurement
ranges from 1.999mW up to 19.99kW.
This unusually wide range makes it suitable for a greater variety of
applications 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 measurement of switch contact resistances to international
High resolution and accuracy
With a lowest range of 1999µW the BS407 can resolve down to one
micro-ohm. Rapid settling minimises delay between readings.
Precision analogue circuitry ensures a high measurement accuracy of up to 0.1% of reading ± 0.1% of scale.
Resolution Test Current F.S. Voltage
250 mA
500 µV
± 0.1% reading ± 0.4% scale
1 µW
1999 µW
Wide measurement range
1 mV
± 0.1% reading ± 0.2% scale
The instrument is protected against the back-emf of its own test current from
any inductance and against external short-term connection to voltage sources
up to 50V.
Protection against greater abuse is provided by non-flammable fusible resistors.
19.99 mW
10 µW
50 mA
199.9 mW
100 µW
10 mA
2 mV
± 0.1% reading ± 0.1% scale
1999 mW
1 mW
5 mA
10 mV
± 0.1% reading ± 0.1% scale
19.99 W
10 mW
500 µA
10 mV
± 0.1% reading ± 0.1% scale
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 (1999µW range). Low battery indication in display.
199.9 W
100 mW
50 µA
10 mV
± 0.1% reading ± 0.1% scale
AC Line
1999 W
50 µA
100 mV
± 0.1% reading ± 0.1% scale
Built-in battery charger allows instrument operation while re-charging.
Nominal re-charge time 12 hours.
19.99 kW
10 W
10 µA
200 mV
± 0.1% reading ± 0.2% scale
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 2000W and 20kW ranges.
Reverse Polarity
Operated by front panel switch. Reverses the polarity of the test current, enabling thermal emf effects to be detected and quantified.
Set Zero
Rotary offset control. A front panel switch can be used to divert the test current way from the unknown, allowing zero adjustment to be undertaken with
the test leads in place.
Source EMF
18 mV ± 2mV with 20mV Clamp Active
< 6V with 20mV Clamp Inactive
> 1V (> 0.5V on 1999µW range). Compliance is the
maximum voltage that can be tolerated from additional
resistance in series with the force connections
Operating Range:
Storage Range:
Electrical Safety:
3.5 digit LCD with 12.5mm characters.
ABS casing with metal tilt stand giving approx. 15o angle.
220 - 240V, 110 - 120V or 100V ±10%, 50/60Hz, adjustable internally; 20VA max. Installation Category II.
+5 C to + 40 C, 20% to 80% RH.
-10 C to +50 C
Indoor use at altitudes to 2000m, Pollution Degree 2.
Complies with EN61010-1.
Complies with EN61326.
220(W) x 88(H) x 230(D) mm, (10.3 x 3.4 x 9.2")
excluding feet and tilt stand.
1.3 kg (3lb).
Supplied with Kelvin Test Clip Leads, Operating Manual, IEC Mains Lead
Carrying Case
Thurlby Thandar Instruments Ltd. operates a policy of continuous development and reserves
the right to alter specifications without prior notice.
Designed and manufactured in Europe by:
Thurlby Thandar Instruments Ltd.
Glebe Road, Huntingdon. Cambs. PE29 7DR U.K.
Tel: +44 (0)1480 412451 Fax: +44 (0)1480 450409
Email: [email protected] Web:
82100-1130 Iss. 1A
Product Summary
Company name and product brands
Laboratory Power Supplies
Bench and system power supplies from 30 watts up to
1200 watts using linear, mixed-mode and PowerFlex
regulation technologies.
Thurlby Thandar Instruments Ltd. (TTi) is one of Europe’s leading
manufacturers of test and measurement instruments.
Waveform Generators
Analog and digital (DDS) function generators, true
arbitrary generators, arbitrary/function generators and
pulse generators.
In the future, however, the full product range will be branded Aim-TTi.
Products have been sold under two brand names:
TTi and Aim.
This changeover will be gradual and many products will continue to carry
the TTi or Aim brands for some time to come.
Web Addresses (URLs)
Precision Measurement Instruments
Benchtop DMMs, frequency counters, component
measurement instruments (LCR), electronic dc loads,
current probes.
The preferred URL for obtaining information concerning Aim-TTi products
is: (international customers)
Customers in the UK should use the URL:
RF and EMC Test Equipment
Spectrum analyzers, signal generators, frequency counters,
power meters, emc measurement instruments.
Customers in the USA should use the URL:
Note that previous URLs such as will continue to operate
for the time being.
Designed and built in Europe by:
Thurlby Thandar Instruments Ltd.
Glebe Road, Huntingdon, Cambridgeshire PE29 7DR England (United Kingdom)
Tel: +44 (0)1480 412451 Fax: +44 (0)1480 450409
Email: [email protected] Web:
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