Intrinsic safety entity verification -6, Intrinsic safety entity verification – Rockwell Automation 1797-OE8 FLEX Ex Analog Modules User Manual User Manual
Page 72
Publication 1797-6.5.1 - May 2005
6-6 Applying 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 pages 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-IE8).
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<10pF/m
Li<0.5uH/m
R<0.1
Ω/m
41665
P/I transmitter
EEx ia IIC T4
Ui=30V
Ii=165mA
Ci=22.5nF
Li=730uH
+
cable length = 10m
+
sig
22
Ω
1797-IE8 Analog Input
EEx ia/ib IIB/IIC T4
Uo<23.7V
lo<92.5mA
91
Ω
17V
IIB
Ca=560nF
La=10mH
IIC
Ca=66nF
La=2.5mH
Module
Uo
Io
Ca
La
Module
Uo<23.7V
Io<92.5mA
Ca=66nF
La=2.5mH
< or =
< or =
> or =
> or =
< or =
< or =
> or =
> or =
Total Loop
Ui
Ii
Ci
Li
Module
Ui=30V
Ii=165
Ci=22.6nF
Li=735uH
Distance
(length
(length
Distance
(10m
(10m
Cable
Ci per length)
La per length)
Cable
Ci=10pF/m)
La=0.5uH/m)
Total Loop
Ui
Ii
Ci
Li
Module
Ui=30V
Ii=165
Ci=22.5nF
Li=735uH
+
+
+
*
*
*
*