Rockwell Automation 1797-OE8H FLEX Ex HART Analog Modules User Manual - Manual (Page 102)

Publication 1797-6.5.3 - March 2006
6-4 Apply FLEX Ex Analog I/O Modules
1797-IE8H Functional and IS Parameters
The figure below provides data, on the Flex Ex analog input modules, which
can be matched to this transmitter.
Loop Functionality Verification
The functional characteristics will be checked first. The figure below shows the
general situation which must be analyzed for proper loop function.
On the left are the module components of the voltage source to run the loop
and its internal source resistance. In the center is the cable. It represents a loss
with regard to its resistance. Cable resistance is a function of cable length. On
the right is the transmitter, which has a minimum voltage it must see to
function properly.
I
Analog Input
V>23V at I = 0 mA
V>17V at I = 22 mA
0…22 mA Measurement Range
EEx ia/ib IIB/IIC T4
Uo<24.4V
Io<92.5 mA
Flexbus
Ca = 119 nF
La = 4 mH
P
+
-V
sig
–
+V
4 to 20 mA
Xmit
273 Ω
23.7V
10 Ω
Bus
uC
HART
modem
Ci<10 pF/m
Li<0.5 uH/m
R<0.1 Ω/m
Ca = 118 nF
La = 4 mH
Transmitter
Minimum
Voltage = 14V
+
–
Cable resistance loss
–
+
Module source voltage = 17V
Module source resistance = 273 Ω
+
sig
10 Ω
Module sense resistance
= 10 Ω
273 Ω
17V