Rockwell Automation 1797-IRT8 FLEX Ex Thermocouple/RTD/mV Input Module User Manual - Manual (Page 58)

Publication 1797-6.5.2 - February 2001
6-4 Applying FLEX Ex Thermocouple/RTD/mV Input Modules
Similarly for RTDs an number of industry standard types are available,
such as PT100, Ni100, etc. Again, the IRT8 is designed to work with a
variety of these types. Functional compatibility is simply a matter of
selecting the correct sensor type when configuring the IRT8 module
with the system I/O configuration software.
Thermocouples and RTDs are known as “simple devices” from an IS
standpoint. Basically this means they either have no mechanism by
which to produce or store energy or they are so simple and produce
such low energy, that they are intrinsically safe.
Below is the IRT8 with its IS entity parameters for the main measuring
input used for thermocouples and RTDs. The example shown is for an
RTD, IRT8 and the loop’s associated wiring.
In the figure above, three items are shown:
•
the field device
•
the interconnecting cable
•
and the Flex Ex module.
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 RTD 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
2W RTD
FLEX
Bus
Bus
uC
+V
Power
Supply
-V
L
H
-
+
-
+
CJC
Thermocouple, RTD, mV Input
EEx ia/ib IIB/IIC T4
Uo=9V, Io=37mA, Po=83mW
IIB IIC
Ca=40uF Ca=4.9uF
La=80mH La=20mH
Lo/Ro=1.7mH/ohm Lo/Ro=0.4mH/ohm
Ci<10pF/m
Li<0.5uH/m
R<0.1ohm/m
Li/R<5uH/ohm
cable length = 10m
2 wire RTD
EEx ia IIC T6
Ui=10V
Ii=100mA
Ci=0
Li=0
Module
Uo<9V
Io<37A
Ca=4.9uF
La=20mH
Lo/Ro=0.4mH/ohm
Transmitter
Ui=10V
Ii=100mA
Ci=0
Li=0
< or =
< or =
> or =
> or =
> or =
Total Loop
Ui=10V
Ii=100mA
Ci=100pF
Li=5uH
Li/R=5uH/ohm
Distance Cable
(10m * Ci=10pF/m)
(10m * La=0.5uH/m)
Li/R=5uH/ohm
+
+
=
=
=
=
=
Module
Uo
Io
Ca
La
Lo/Ro
Transmitter
Ui
Ii
Ci
Li
< or =
< or =
> or =
> or =
> or =
Total Loop
Ui
Ii
Ci
Li
Li/R
Distance Cable
(length * Ci per lengh)
(length * La per length)
Li/R
+
+
=
=
=
=
=