Rockwell Automation 1797-IRT8 FLEX Ex Thermocouple/RTD/mV Input Module User Manual - Manual (Page 61)

Publication 1797-6.5.2 - February 2001
Applying FLEX Ex Thermocouple/RTD/mV Input Modules 6-7
General Example
Entity parameters allow a user to design an instrumentation loop by
selecting entities such as I/O, wiring and field devices that meet
parameters defined by local manufacturers and certifying agencies.
For example, a user may have an input channel and a transmitter
sending that channel information.
In this application, the transmitter can withstand:
– maximum input voltage (U
i
)=40V and
maximum input current (I
i
)=100mA
while the input will provide:
– maximum output voltage (U
o
)=28V and
maximum output current (I
o
)=93mA
In the same application, the transmitter’s:
– maximum internal capacitance (C
i
)=0.5nF and
maximum internal inductance (L
i
)=1mH
are both less than the input’s:
– allowed capacitance (C
o
)=66nF and
allowed inductance (L
o
)=2.5mH will accept
According to the defined entity parameters, this example’s
combination is compatible. Interconnect wiring and communications
ports must also be considered in regard to the entity parameters.
Interconnect Wiring
Interconnect wiring is rated with maximum internal capacitance (C
i
)
and maximum internal inductance (L
i
) on a per foot/meter basis. The
actual length of cable must be multiplied by these parameters and
considered with the any application.