Rockwell Automation 1797-OE8H FLEX Ex HART Analog Modules User Manual - Manual (Page 104)

Publication 1797-6.5.3 - March 2006
6-6 Apply FLEX Ex Analog I/O Modules
Intrinsic Safety Entity Verification
Next we must determine if the pressure to current analog transmitter and the
Flex Ex analog input module are compatible from an IS perspective. We will
make this determination for a IIC gas application.
The figure below shows an extraction of pertinent information from the
figures on page 6-3.
In the figure above, three key items are shown, the field device the
interconnecting cabling and the Flex Ex module (in this example, a
1797-IE8H). The entity verification is done for the gas group IIC. As the table
shows, the module’s entity parameters are compared to the combination of the
transmitter and the wiring entity parameters.
The module’s entity parameters are shown in the Module column on the left.
They must be compared with the parameters shown in the Total Loop column,
in the manner shown. The values in the Total Loop column are determined in
the following manner:
• Total Loop U
i
= Transmitter U
i
• Total Loop I
i
= Transmitter I
i
• Total Loop C
i
= (Transmitter C
i
+ Cabling C
i
per length) X (cable
length)
• Total Loop L
i
= (Transmitter L
i
+ Cabling L
i
per length) X (cable
length)
As long as the Module and Total Loop entity parameters satisfy the inequalities
shown the loop is acceptable for use in the hazardous environment.
=
=
=
=
=
=
=
=
Ci<10 pF/m
Li<0.5 uH/m
R<0.1 Ω/m
P/I transmitter
EEx ia IIC T4
Ui =3 0V
Ii = 165 mA
Ci = 22.5 nF
Li = 730 uH
+
Cable length = 10m
+
sig
10 Ω
1797-IE8H Analog Input
EEx ia/ib IIB/IIC T4
Uo<24.4V
lo<92.5 mA
275 Ω
23.7V
Ca = 119 nF
La = 4 mH
Module
Uo
Io
Ca
La
Module
Uo<24.4V
Io<92.5 mA
Ca=119 nF
La=4 mH
< or =
< or =
> or =
> or =
< or =
< or =
> or =
> or =
Total Loop
Ui
Ii
Ci
Li
Module
Ui=30V
Ii=165
Ci=22.6 nF
Li=735 uH
Distance
(length
(length
Distance
(10 m
(10 m
Cable
Ci per length)
La per length)
Cable
Ci=10 pF/m)
La=0.5 uH/m)
Total Loop
Ui
Ii
Ci
Li
Module
Ui=30V
Ii=165
Ci=22.5 nF
Li=735 uH
+
+
+
*
*
*
*