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3.1.4. Grounding Consideration
Indiscriminate grounding of instruments can introduce ground loop interference. To pre-
vent this influencing the measuring and analyzing instruments with which the 1050 is
used, it is important that all signal ground lines of the instruments are grounded at one
point only in the measurement system. To do this without prejudicing the operating
safety of the instruments, proceed as follows:
1.
Ensure that all instruments are switched off prior to checking their
Signal Ground
&
Chassis
connections and interconnecting the equipment.
2.
Connect the signal ground lines of all instruments together. This is done automati-
cally though the screens of the input and output cables used to interconnect the
instruments.
3.
Where the same instruments are interconnected by more than one signal cable or a
combination of signal and remote control cables, each containing a signal gound
connection, keep the cables short and close together or disconnect the signal
ground connection of all but one of them.
4.
Where non-IEC 348 Safety Class I or II instruments are used, disregard item 5 and
check that the signal ground line and chassis of these instruments are connected to
mains ground, either via their mains connector or via one of their ground terminals.
In addition keep their power cables and ground lines short and close together and
check that the measurement transducer is electrically insulated from grounded mea-
surement sources.
5.
Where instruments with mains connectors including a protective earth-chassis con-
tact are used, check that (a) one and only one of these instruments has its signal
ground line connected via chassis to mains ground and (b) the housing of the mea-
surement transducer is electrically insulated from grounded measurement sources.
6.
Where the measurement arrangement is used free-standing without the instrument
cabinets touching, check that each of the other instruments in the measurement
arrangement has its chassis connected to (a) mains ground only or (b) signal ground
only. With instruments having a mains connector with protective earth-chassis con-
tact (a) is to be preferred.
7.
Where the measurement arrangement is mounted in an instrumentation rack, 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 a mains connector
having a protective earth-chassis contact). If more than one of the instruments has a
permanent
Signal Ground & Chassis
connection, then isolate the cabinets of these
instruments from the rack using isolating flanges for mounting.
On the 1 050 rear panel the signal ground may be disconnected from chassis by
removing the metal link connecting the
Signal Ground & Chassis.
For stand alone
use of the instrument the
Signal Ground & Chassis
must always be kept intercon-
nected.
In addition to the above, the 1050 has a switch, adjacent to the
Voltage
and
Charge
Input
on its rear panel, for selection of either floating or grounded input modes with
respect to the vibration meter and compressor circuits of the instrument. Conse-
quently a ground loop, completed by the compressor feedback loop, can be broken
by setting the switch to
"Floating"
mode. However, these inputs should be connect-
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