Megger BT51 Data sheet

BT51

Low Resistance Ohmmeter

■ High test current

■ Four terminal measurement

■ Two measuring ranges (2000 mΩ and

20,00 mΩ) and maximum resolution of
0,01 mΩ

■ Protected against inadvertent connection

to the mains supply

BT51

Low Resistance Ohmmeter

DESCRIPTION

The BT51 Low Resistance Ohmmeter makes measurements by passing
a current through the conductor under test and also monitoring
the voltage across it. The test current is limited by a simple current
limiting circuit and is measured by monitoring the voltage across a
resistor. The test current is maintained at a nominal 2 A, and as the
measurement is ratiometric, the reading is unaffected by any current
variations.

The instrument has a 3 1/2 digit LED display to facilitate use in low
light levels. Two LED’s on the front panel indicate battery condition
and whether test current is flowing when a measurement is being
made. A neon lamp indicates the presence of a dangerous voltage if
the test spikes are accidentally placed across a live circuit. This warning
takes place whether or not the instrument has been switched on.

The ohmmeter is protected up to 240 V a.c. by a relay circuit that
keeps the instrument in a safe mode isolated from the mains supply.
Again, this safeguard is effective whether or not the instrument has
been switched on.

Operation of the instrument is simple, there being only one range
switch to set. Power is supplied by internal rechargeable cells and the
charger unit is incorporated into the case. Duplex Connect hand spike
test leads are supplied and other types of leads are available.

The instrument is built into a robust, portable case that is weatherproof
and shockproof and has a hinged, detachable lid.

NEW DUPLEX CONNECT TEST LEADS – NOW SUPPLIED AS
STANDARD

n Carry one lead set and swap terminations

n Simple push and twist for a quick change

n Lockable twist cap secures the leads

n Extension leads available

DH1-C

Juego de cable con palanca doble 3 m, con conexión (x2)

1006-442

3 m duplex handspike lead set, with connector (x2) 1006-442 Two
wire, four terminal duplex twist probe lead set 3 m long.

Consists of the following:-

DTP1-C duplex twist probe x2

TL3-C-BT51 3 m lead connector x2

BT51

Low Resistance Ohmmeter

The Megger DLRO duplex connector four terminal test lead system
is designed to provide the most cost effective and convenient way
to provide the user with all off the test lead terminations and lead
lengths required for the many different applications encountered in
low resistance testing.

At the centre of this unique test lead system is a bespoke connector
allowing terminations such as kelvin clips or duplex test probes to be
changed as required.

APPLICATION

Instruments that measure low resistance accurately and give the
result directly are invaluable in many applications. The BT51 is a
stable, accurate, reliable, low resistance ohmmeter equally suited to
precision laboratory applications and to applications in the field.

Example Uses

Commissioning and maintenance of substation equipment, where
measurements can be made on such things as busbar joints, switch
and circuit breaker contact resistance, fuse resistance, cold lap
welded joints in aluminium earthing strip and earth bonding

Maintenance of overhead transmission lines, where “hot” joints can
be tested before and after their remaking or recompression

Bond testing aircraft frames, including the bonding of electronic
dischargers and fuel tanks

Testing earth bonds in mines

Rail bond testing, where a rail is used as part of a communication
system or for power transmission

resistance RX is measured only between points A and B; other
resistances in the current loop either side of A and B are ignored.

Good connections to the item whose resistance is being measured
are very important. Test leads for the instrument may take the form
of duplex hand spikes, which enable connections to such things as
busbars and aircraft frames to be made easily. Crocodile-type clip
leads are used where a more rigid connection is necessary (e.g., when
varying contact resistance tends to introduce errors). Sometimes the
current connections are made with crocodile clips and the potential
connections with spikes. This may be the case, for example, where
multiple measurements have to be made.

FEATURES AND BENEFITS

n High test current - 2 A DC (e.g., for aircraft bond testing)

n Four terminal measurement

n Two measuring ranges (2000 mΩ and 20,00 mΩ) and

maximum resolution of 0,01 mΩ

n 3 1/2 digit LED display, which is helpful in a poorly lit

environment

n Protection against 240 V a.c. and warning lights for added

safety

n Robust, shockproof, weatherproof, portable case

n Can used very long test leads

Testing the integrity of lightning conductors

Electronic equipment, where measurements can be made on such
things as resistors, track resistance of printed circuit boards (quality
control of plating thickness), resistance of plated-through holes on
printed circuit boards, contact resistance of relays, resistance of
shunts, thick film circuits, etc.

Domestic and industrial wiring installations, where ring main
continuity and circuit protective conductor continuity can be
measured and the integrity of earth bonding checked in compliance
with the l6th Edition IEE Wiring Regulations

PRINCIPLE OF OPERATION

The BT51 uses the four-terminal method of measurement. The main
advantage of this method is that the resistance of the test leads is
not included in the measurement. This is an important factor when
the value of the measured resistance is very low. In the diagram,

2