CHAPTER 3
Operation
7
the protective (green/yellow) conductor of the cable should be connected to a suitable earth,
such as the earth contact of a mains outlet socket. The use of an extension cable without
protective conductor should be avoided for safety reasons.
In countries where use of mains socket outlets without protective conductor is standard, the
mains supply should incorporate an authorized earth leakage current circuit breaker.
Grounding Considerations
The signal ground line of Type 2719 is permanently connected to its chassis. This is done at
one point only to give the best possible immunity to mains-carried noise. Nevertheless, when
using the amplifier in complex measurement setups, indiscriminate grounding of the instrument
signal ground lines may introduce mains hum. This can be avoided by ensuring that the signal
ground line of the entire measurement setup is grounded at one point only. To do this without
prejudicing the operating safety of the instruments involved:
1) Connect the signal ground lines of all instruments together. This is done automatically
through the screens of the input and output cables used to interconnect the instruments.
2) If instruments equipped with a mains socket protective earth terminal are employed in the
measurement arrangement then check that:
a) one and only one of these instruments has its signal ground line connected via
chassis to mains ground
b) the housing of the measurement transducer is isolated from measurement objects
3) If the measurement arrangement is used free-standing without instrument cabinets touching,
then ensure that the method in which to connect the signal ground line for each instrument
in the measurement arrangement is consistent – either each one is connected to the mains
ground, or each is connected to its chassis. Mains ground is preferred for instruments with
a mains socket chassis terminal.
4) If the measurement arrangement is mounted in a metal instrumentation rack, then ensure
that one and only one of the instruments has its signal ground line connected to chassis
(and chassis connected to mains ground if equipped with mains socket chassis terminal). If
more than one of the instruments has a permanent signal ground chassis connection, then
isolate the chassis of these instruments from one another.
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