Honeywell Searchline Excel, Техническое руководство

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18
MAN0530 Issue 10 - 11/09 Searchline Excel
2104M0506
3. INSTALLATION AND OPERATION
3.3 ELECTRICAL CONNECTIONS
3.3.1 General
All ranges of Searchline Excel comply with the EMC requirements EN50270. In order to
maintain compliance with these standards it is essential that the electrical installation of Excel
is engineered correctly.
Electrical installation standards vary for different countries, companies and applications and it
is the responsibility of the installation design authority to determine the applicable standards
and ensure compliance with them. When designing electrical installations for Excel, Honeywell
Analytics recommend that the installation design authority considers the following:
a. The unit cases should not, if possible, be connected to electrically noisy (
dirty
) metalwork
or conductors. Preferably, the case (internally connected to the green / yellow GND wire)
should be connected to a low noise instrument (
clean
) earth. See also para e. below. In
order to facilitate electrical isolation of the Searchline Excel from a noisy earth an isolation
kit is supplied. This kit should be fitted as standard unless local regulations forbid this.
b. The entire length of the field cabling connected to each unit should be fully shielded. This
should be connected to a low noise (
clean
) earth.
c. The low noise instrument (
clean
) earth system should only be connected to safety earth
(usually
dirty
) at a single point on the entire site/installation. This connection should be
made in such a manner that it does not introduce noise onto the low noise instrument
earth. Star earthing arrangements minimise earth current crosstalk.
d. The shields of the field cabling should not be connected such that earth loops are
produced, or in a manner that will result in the shields carrying large currents from heavy
plant or equipment.
e. Ideally, the field cable shield should be connected to the unit’s green/yellow GND wire,
providing a single, continuous earth shield. This connection must not be allowed to
complete an earth loop.
f. The earth bonding arrangement must ensure that the maximum peak voltage between
the unit case earth and any field cable conductor is less than 350V. Voltages in excess
of this can cause permanent damage to the unit’s RFI protection filters.
g. The use of a single, screened cable for each gas detector ensures maximum screening
and minimum crosstalk. Cabling arrangements which use a single cable for connecting
a number of field devices compromise screening, increase the potential for crosstalk and
prevent implementation of true star earthing.
h. Any electrical interference induced onto the 4 - 20mA loop conductors by the installation
must be kept below the levels necessary to comply with the general requirements of
EN 60079-29-1:2007 &, IEC 60079-29-1:2007. In practice, this means that peak noise
currents induced on the current loop should be no greater than ± 0.25mA
j. The 0V rail of the control card/control system is directly connected to one side of the 4
- 20mA current sensing resistor. Electrical noise on this rail is therefore directly connected
to the 4 - 20mA input. In order to avoid additional noise being induced on the 0V rail, it
should not be commoned with the safety earth/ground, which frequently carries a high
level of electrical noise.