STATUS SCIENTIFIC CONTROLS
FGD3 Infrared Gas Detector Heads
TD06/024
Issue:
7
Change Note:
1904
Page 9
3.6 Installation in Hazardous Areas
When used in a hazardous area, the FGD3 detector requires an intrinsically safe (I.S.)
power supply. This can be provided in two ways:
1. By using the MCU Control Unit incorporating the I.S. Output Module Type
FGDIO. The FGDIO module is incorporated within the MCU control unit
enclosure and provides intrinsically safe outputs for all versions of the FGD
range of gas detectors.
2. By using proprietary safety barriers.
When using barriers to create an I.S. supply, certain restrictions are imposed on the
parameters of the interconnecting cables used. These parameters are defined by the
manufacturer of the barrier and limit the maximum capacitance, inductance and
inductance to resistance ratio of the cable. The installation is only intrinsically safe
when the combination of the barrier and connecting cables comply with the
manufacturer’s specification.
As with a non-I.S. installation, the cable length is restricted by the cable loop
resistance. With the introduction of a barrier or the FGDIO module (refer to the MCU
System Installation and Hardware Configuration Manual), the cable loop resistance is
reduced because of the internal resistance of the barrier. The end-to-end resistance of
the barrier must therefore be subtracted from the overall cable loop resistance when
calculating cable lengths.
Barriers must be selected to restrict the parameters of the I.S. supply to the gas
detectors within the following limits:
Terminals
U
max
I
max
P
in
Ci
Li
0V and SIG
30V
0.15A
0.81W
10nF
0
0V and +
7.5V
0.75A
1.4W
9.7
F
0
When considering the capacitance and inductance allowable across the barrier output
terminals, note:
There is 10nF and zero inductance between terminals 0V and SIG on any model
of FGD Detector head.
There is an equivalent of 9.7
F capacitance and zero inductance between
terminals 0V and + on the FGD3 Infrared gas detector.
Guidance on the correct installation of I.S. systems is provided by EN60079-14:2014
Summary of Contents for FGD 3 Series
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