WIKA RTD Zusatzinformation Seite 22

5. Calculation examples for self-heating at the sensor ...
Sensor without transmitter, with barrier
EN
ϑ
C / L = capacitance and inductance of the electrical connecting cable
c c
Simplified verification of intrinsic safety for the above-mentioned combination
Measuring insert
U : DC 30 V
i
I : 550 mA
i
Pi (max) at the sensor = 1.5 W
Ci: negligible
Li: negligible
n/a = not applicable
Upon comparing the values, it is obvious that it is permissible to connect these instruments
to one another. However, the operator must also take into account the values for
inductance and capacitance of the electrical connection leads.
These calculations apply to the Z954 Zener barrier in connection with a resistance
thermometer Pt100 in 3-channel mode without grounding, i.e., symmetrical operation of
the resistance thermometer in 3-wire circuit on a display or evaluation instrument.
22
Hazardous area
U ≥ U
i o
l ≥ l
i o
P ≥ P
i o
C + C ≤ C
i c o
L + L ≤ L
i c o
Zener barrier Z954
≥ U
≥ I
o
≥ P
o
≤ C
≤ L
o
WIKA additional information RTD and TC, intrinsically safe designs (Ex i)
Non-hazardous area
: DC 9 V U : AC 250 V
o m
: 510 mA I : n/a
i
: 1,150 mW P : n/a
i
: 4.9 µF C : n/a
o i
: 0.12 mH L : n/a
i