General Description - Megger BT51 Guia Del Usuario

General description

The BT51 uses the four terminal measurement principle. Current generated
within the instrument, passes between the current terminals C1 and C2 via
the test sample. The voltage across the test sample is measured across the
potential terminals P1 and P2.
The test current, of nominally 2A, is measured by monitoring the voltage
drop across an internal series resistor. The instrument compares this
voltage with the voltage across the P1 and P2 terminals and a ratiometric
measurement is performed. On the lower range a voltage amplifier is used.
Because the measurement is ratiometric the reading is unaffected by minor
variations of test current.
There are two measuring range, 2000 mW and 20 mW, selected by the
rotary switch that is also used to turn the instrument off. The readings are
indicated on a 3 ⁄ digit light emitting diode display which is easily seen in
1
2
poor lighting conditions.
A green L.E.D. indicator light glows when the test current is passing
between the C1 and C2 terminals as a test is made. A red neon light
adjacent to the terminal, illuminates as a warning of the presence of a
dangerous voltage, should the test lead probes be accidentally placed
across a "live"circuit. The instrument incorporates a relay protection
circuit (effective up to 240 V a. c. ) should such a connection occur. This
protection becomes operative at low voltages and the neon warning light
shows when a dangerous voltage is present. Both the neon warning light
and the protective relay are effective irrespective of whether or not the
instrument has been turned on prior to the probes being placed across the
voltage source.
6
Power for the instrument and the test circuit is obtained from internal
rechargeable NiCd cells. When the battery needs recharging a red L.E.D.
"low battery voltage" warning light illuminates next to the display. An
integral charger unit is fitted accompanied by a warning neon light to show
when the battery is under charge, and a fuse for protection.
Note :- It is advisable to ensure that the battery cells are fully
charged before embarking upon any tests.
The instrument is contained in a robust plastic case with a hinged
detachable lid that will automatically become unclipped if it is accidentally
thrown or dropped open, thus preventing damage to the hinges.
A variety of test lead set, some with duplex handspikes are available as
optional extras.