Filter
Top Products
Model TS420
16
5.1.5 Intrinsically Safe System Requirements
NOTE - Refer to control drawing 45217 Rev A. (Section 5.2.2)
The TS420 is approved as intrinsically safe on its own (entity approved). However, when
installing the TS420 into a system, there are requirements, which must be strictly followed to
maintain the intrinsic safety of the system. These requirements are:
1. U
i
/V
MAX
of the field device (TS420) must be less than or equal to U
MAX
of barrier.
2. I
i
/I
MAX
of the field device (TS420) must be greater than or equal to I
MAX
of the barrier.
3. The inductance of the cable and the TS420 (L
i
) must be less than the barrier’s maximum
inductance rating (La).
4. The capacitance of the cable and the TS420 (C
i
) must be less than the barrier’s maximum
capacitance rating (Ca).
To calculate maximum cable length, use the following formulas, and use the shorter of the two
calculations.
Capacitance:
Max. Cable Length = C
MAX
(Barrier) - C
i
(TS420) (ft)
Wire Capacitance/Ft
Inductance:
Max. Cable Length = L
MAX
(Barrier - L
i
(TS420) (ft)
Wire Inductance/Ft
5.1.6 Sample Calculation
What is the maximum allowable cable length when using an MTL 7206 barrier and BELDEN
8760 2-conductor shielded cable?
BELDEN 8760 Parameters: C/ft = 24 pF/ft, L/ft: not available
MTL 7206
: TS420:
C
MAX
= 0.12 µf C
i
= 0 µf
L
MAX
= 4.0 mH L
i
= 500 µH
U
i
/V
MAX
= 35V U
i
/V
MAX
= 35V
I
i
/I
MAX
= 93mA I
i
/I
MAX
= 100mA
1. U
i
/VMAX (TS420) ≤ U
i
/VMAX (MTL 7206)
35VDC ≤ 35VDC
2. Ii/IMAX (TS420) ≥ Ii/IMAX (MTL 7206)
100mA 93mA
3. Cable inductance not available.
4. Max. cable length = C
MAX
(MTL 7206) - C
i
(TS420)
C/L (Belden 8760)
= 0.12µf - 0µf
24pF/ft
Max. Cable length = 5000 feet