Polarity Reverse Control; Overload Protection - Megger AVOMETER 8 Mk7 Guia Del Usuario

which they are presented, they depend for their
accuracy, not only upon their initial calibration,
but also upon the maintenance of a sinusoidal
waveform. Since the form factor (r.m.s. value
divided by mean value) of a sine wave is 1,11,
this has been taken into account in calibrating the
meter, which does, therefore, indicate r.m.s.
values on the assumption that the normal sine
wave will be encountered. Generally speaking,
considerable waveform distortion can occur
without appreciably affecting the form factor and
resulting accuracy of measurement, but the user
should recognise the possibility of some error
when using distorted waveforms, near square
wave-shapes producing high readings and peaky
ones, low readings.

POLARITY REVERSE CONTROL

If d.c. voltage is required both positive and
negative with respect to a reference point, or the
direction of current flow is reversed, in order to
simplify the matter of lead alteration, a polarity
reverse push-button marked 'Rev MC' is
provided. It should be noted that the polarity
indicated at the terminals is for normal use and
does not apply when the 'Rev MC' button is in
the raised position. The button is a self latching
type and must be pressed to release for reversal
of meter movement direction.
8

OVERLOAD PROTECTION

One of the most attractive features of the
instrument is the provision of an automatic cut-
out which gives a very high degree of overload
protection, and imparts to the user a feeling of
confidence.
If an overload is applied to the meter, either
forward or in reverse, the 'Cut-Out' button
springs up from its normal position, thus breaking
the main circuit and the red portion of the button
will now be extended. This button has only to be
depressed its full amount to render the instrument
ready to use again. It is important to note that the
cut-out should never be reset when the
instrument is connected to an external circuit, and
the fault which caused the overload should be
rectified before the meter is reconnected.
Although the overload mechanism gives almost
complete protection to the meter, it cannot be
guaranteed to completely fulfil its function in the
very worst cases of misuse, such as the mains
being connected across the meter when set to a
current range. It should be noted that mechanical
shock to the instrument will sometimes trip the
cut-out mechanism. Additional protection is
provided on resistance ranges by a 1 A fuse
connected in the circuit on the 'Ω x 1' and 'Ω x
100' resistance ranges.