BRUEL & KJAER 1618 - Grounding Considerations; Operation with Measuring Amplifiers Alone

Once the line voltage setting and fuse have been checked, the line supply may be con-
nected
to the LINE input socket using the Power Cable AN 0010 supplied. To fit a suit-
able mains plug to the cable see Fig.3 .1.
For
maximum operating safety it is recommended that the protective (green and yellow)
conductor of the cable be connected to a suitable ground, such as the protective ground
contact of a line socket outlet. The use of an extension cable without a protective ground
conductor should be avoided.
3.1.4. Grounding Considerations
When several instruments are used together, ground loops and their resulting problems
can easily be formed . Therefore, the following procedure is necessary to ensure that the
system is free from ground loops, by connecting each instrument in the arrangement to
ground via the same path .
1.
Connect the signal grounds of all the instruments together (this automatically occurs
through the screens of the signal cables). However, if two instruments are con-
nected in parallel, it may be necessary to disconnect one of the screens in the signal
cables to prevent formation of a loop.
2 .
Connect the signal ground to the chassis, and the chassis to the mains ground of
one instrument only , preferably the one closest to the measuring point.
3 . Check each of the other instru ments in the system to verify that its chassis is con-
nected to one and only one of the following : mains ground, si gnal ground , or the
chassis of another instrument .
The signal
ground and chassis of the Type 1617 are normally connected by the metal
strap between the ground terminals on the rear panel. The strap must be removed to iso-
late
the signal ground from chassis ground .
3.2. OPERATION WITH MEASURING AMPLIFIERS ALONE
14
The Measuring Amplifiers Type 2606, Type 2607, and Type 2608 are amplifiers cover-
ing
the frequency range 2 Hz to 200 kHz. They are designed for sound and vibration
measurement. accepting inputs from a wide range of transducers and preamplifiers .
They can supply 12 volts DC for preamplifier power supplies, or the 200 volt polarization
voltage
and 150 volt anode supply for B & K condenser microphones. They contain selec-
table
frequency - weighted networks for sound level measurement. and high and low pass
filters to limit the frequency range for audio frequency measurements .
An external filter such as the Type 1617 can be connected in series with, or in place
of, the internal weighting networks and filters to permit frequency analysis. Such an ar-
rangement is shown in Fig .3 .2. Indication of the signal level can be obtained either from
the built-in meter , or from a permanent record obtained on a Level or X-V Recorder con-
nected to the measuring amplifier 's output. see section 3 .3 .
For
further information on measur ing amplifiers to help in deciding the best for a particu-
lar application , a more comprehensive review of the capabilities of the Measuring Ampli-
fier is gi ~ en in section 1. See also the relevant Product Data sheets .