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I.S. Field Display User’s Manual
Michell Instruments
5
INSTALLATION
2.2.2 Remote
Indication
Hazardous Area
Safe Area
ppm
V
Easidew PRO I.S. Field Display
P
E
S
S
S
+
0
9999
4-20 mA
4-20 mA
3
1
Single channel
Zener barrier
Instrument
with
isolated
4-20mA
output
ppm
V
Easidew PRO I.S. Field Display
P
E
S
S
S
S
+
0
9999
4-20 mA
4-20 mA
3
1
Galvanic
Isolator
Instrument
with
non-isolated
4-20mA
output
ppm
V
Easidew PRO I.S. Field Display
P
E
S
S
S
S
+
0
9999
4-20 mA
4-20 mA
3
1
Two channel
Zener barrier
Instrument
with
non-isolated
4-20mA
output
The I.S. Field Display may be used to provide
a remote display within a hazardous area
driven via an intrinsically safe interface
from a 4-20 mA safe area signal. The type
of intrinsically safe interface is not critical.
Either a Zener barrier or a galvanic isolator
may be used, providing that the Ui, li and Pi
of the I.S. Field Display are not exceeded and
the voltage capability of the 4-20 mA signal
is sufficient to drive the I.S. Field Display plus
the interface.
When a high integrity earth connection is
already available, a Zener barrier is usually the
least expensive option. If an earth connection
is not available or isolation is required, a
galvanic isolator is the correct choice.
If one side of the 4-20 mA current loop may
be earthed, a single channel Zener barrier
provides the lowest cost protection. If the
4-20 mA signal is not isolated, then two Zener
barriers, a two channel Zener barrier or a
galvanic isolator must be used.
Figure 4 shows the alternative circuits which
may be used.
Figure 4
Alternative Circuits for Remote Indication in a Hazardous Area
Summary of Contents for Easidew PRO
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Page 57: ...I S Field Display User s Manual Michell Instruments 51 NOTES...
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