Rockwell Automation 1797-IRT8 FLEX Ex Thermocouple/RTD/mV Input Module User Manual - Manual (Page 59)

Publication 1797-6.5.2 - February 2001
Applying FLEX Ex Thermocouple/RTD/mV Input Modules 6-5
Total Loop column, in the manner shown. The values in the Total
Loop column are determined in the following manner:
•
Total Loop U
i
is equal to the transmitter U
i
.
•
Total Loop I
i
is equal to the transmitter I
i
.
•
Total Loop C
i
is the addition of the transmitter C
i
and the cabling
C
i
per length multiplied by the cable length.
•
Total Loop L
i
is the addition of the transmitter L
i
and the cabling
L
i
per length multiplied by the 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.
Using the Entity Method
The entity method of device to device electrical interconnect in
hazardous areas certifies individual products for use in those areas (as
opposed to the Loop Method which certifies specific instrumentation
loops for use in hazardous areas).
Using the entity method, individual products are certified based on
their intrinsic ability to produce/store energy and produce/reject heat.
Each part of an instrumentation loop is individually certified and
specified with a set of entity parameters.
Because the FLEX Ex system has been designed to use the entity
method in hazardous areas, the user can design application-specific
instrumentation loops by appropriately matching the devices to be
interconnected.