Det-Tronics GTS Sensor Module User Manual

Page 10

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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

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