Det-Tronics GTS Sensor Module - Manual (Page 10)

8 9.1 95-8616
InTRInSIC SAfETY bARRIERS
When the GT3000 is used in an intrinsically safe
installation, care must be taken when selecting an I.S.
barrier to ensure proper function of the device. The
GT3000 has been tested with the types of barriers listed
in Tables 3 and 4.
Table 3 lists zener barriers. The third column gives the
range of input voltage to the barrier. The upper limit is
set by the barrier. The lower limit is limited by voltage
drops in the 4-20 mA loop with a maximum of 10 Ohms
of resistance in each leg of the loop.
Table 4 lists isolating barriers that provide a wider range
of input power supply voltages and are less dependent
on voltage drops in the loop. Input voltage to the barrier
is specified by the barrier manufacturer.
For additional information regarding proper IS
installation, refer to the Control Drawings in Appendix
C of this manual.
GUIDElINES FOR INTRINSIC SAFETY WIRING
Intrinsically safe systems must be installed in
accordance with the approved control drawings for
the field equipment and the intrinsic safety barriers.
Capacitance and inductance of interconnecting wiring
must always be included in wiring calculations.
Shielded twisted pair cables with at least 18 AWG
conductors are recommended to ensure circuit
performance.
The intrinsically safe conductors must be separated
from all other wiring by placing them in separate
conduits or raceways, or by an airspace of at least 2
inches (50 mm). When located within an enclosure, the
conductors can be separated by a grounded metal or
insulated partition. Wires must be tied down to prevent
loosening and/or shorting.
Intrinsically safe wiring must be identified. Raceways,
cable trays, open wiring, and terminal boxes must be
labeled as Intrinsically Safe. Intrinsically safe wiring
may be light blue in color when no other conductors
colored light blue are used.
Wiring enclosures should be located as close as
possible to the hazardous area to minimize cable runs
and reduce total capacitance of the wiring.
A high quality intrinsic safety ground is required. Some
general rules for grounding intrinsically safe systems are:
• The maximum impedance of the grounding
conductor between the barrier ground terminal and
the main ground point must be less than 1 ohm.
• The grounding conductor must be a minimum of 12
AWG.
• Redundant grounding conductors are recommended
to facilitate testing of the ground connection.
• The grounding conductor should be insulated and
protected from the possibility of mechanical damage.
wIRIng PRoCEdURE
Wire the transmitter as shown in Figures 7 through 12.
CaUtIon
If ripple on the main power source causes
interference with the HART function, the use
of an isolated power source (Figure 12) is
recommended for best HART performance.
Manufacturer P/n
Turck MZB87PX
MTL MTL7787P+
Pepperl & Fuchs Z787.h
Table 3—Acceptable Intrinsic Safety Barriers
for use with GT3000 – Zener Barriers
Manufacturer P/n
Turck IM33-11Ex-Hi
MTL 5541
Pepperl & Fuchs KCD2-STC-Ex1
Stahl 9160/13-10-11
Table 4—Acceptable Intrinsic Safety Barriers
for use with GT3000 – Isolating Barriers