WIKA RTD User Manual

WIKA operating instructions RTD and TC, intrinsically safe designs
3345267.08 06/2011 GB/D
35
GB
Additional information
Temperature class for T3 = 200 °C
Safety margin for type-examined instruments (T6 to T3)*1 = 5 K
Safety clearance for type-examined instruments (T1 to T2)*1 = 10 K
*1 EN/IEC 60 079-0: 2009 Section 26.5.1
9.3 Calculation example for the above-mentioned resistance thermometer with thermowell
RTD measuring insert Ø 6 mm without transmitter, built into a 3F design multi-part thermowell .
Thermal resistance [R
th
in K/W] from table = 37 K/W
Self-heating: 1.15 W x 37 K/W = 42.55 K
T
max
= T
M
+ self-heating: 150 °C + 42.55 °C = 192.55 °C
The result shows, in this case, substantial self-heating at the probe tip.
As safety margin for type-examined instrument (for T6 to T3), an additional 5 °C must be
subtracted from the 200 °C; hence 195 °C would be permissible. This means that in this case
temperature class T3 is not exceeded.
Simplied verication of intrinsic safety for the above-mentioned combination
Measuring insert Zener barrier Z954 Display instrument
(non-hazardous area)
U
i
: DC 30 V U
o
: DC 9 V U
m
: AC 250 V U
o
: AC 230 V
I
i
: 550 mA I
o
: 510 mA I
i
: nA I
o
: nA
P
i
(
max
) at the sensor: 1.5 W P
o
: 1150 mW P
i
: nA P
o
: nA
C
i
: negligible C
o
: 4.9 µF C
i
: nA C
o
: nA
L
i
: negligible L
o
: 0.12 mH L
i
: nA L
o
: nA
Upon comparing the values, it is obvious that it is permissible to connect these units 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.
Electrical connection
For sensor connections, terminal, cable or connector assignments, see chapter
"6.1 Electrical connection".
9. Calculation examples for self-heating at the sensor/thermowell tip

WIKA RTD Specifications

General

Brand	WIKA
Model	RTD
Category	Measuring Instruments
Language	English