WIKA TR25 - Handbuch (Seite 22)

14073045.01 10/2013 GB/D
22 WIKA operating instructions model TR25 (Ex i)
GB
P
i
= in the housing: depending on the transmitter/digital display
C
i
= depending on the transmitter/digital display
L
i
= depending on the transmitter/digital display
The transmitters and digital displays used must have their own certification in accordance
with EN/IEC. The installation conditions and electrical connection values can be seen from the
relevant approvals and must be observed.
8.3 Electrical data with built-in transmitter in accordance with the FISCO model
The transmitters/digital displays used for the application range in accordance with the FISCO
model are considered FISCO field units. The requirements in accordance with EN/IEC 60079-27,
and the connection conditions of the approvals in accordance with FISCO, apply.
9. Calculation examples for self-heating of the tubular body at the
sensor installation point
In-line resistance thermometer model TR25 with built-in head-mounted transmitter model T32.1S.
Power supply is, for example, via a model KFD2-STC4-EX1 transducer power supply (WIKA
Article No. 2341268).
T
max
is obtained by adding the temperature of the medium and the self-heating. The self-heating
depends on the supplied power P
o
of the transmitter and the thermal resistance R
th
.
The following formula is used for the calculation: T
max
= P
o
x R
th
+ T
M
T
max
= Surface temperature (max. temperature of the tubular body at the sensor installation point)
P
o
= From transmitter data sheet
R
th
= Thermal resistance [K/W]
T
M
= Temperature of the medium
Prerequisite is an ambient temperature T
amb
of -20 ... +40 °C.
Thermal resistance for the TR25 (R
th
) 60 K/W
Example
Temperature of the medium: T
M
= 150 °C
Supplied power: P
o
= 15.2 mW
Temperature class T3 (200 °C) must not be exceeded
Thermal resistance [R
th
in K/W] = 60 K/W
Self-heating: 0.0152 W x 60 K/W = 0.91 K
T
max
= T
M
+ self-heating: 150 °C + 0.91 °C = 150.91 °C
The result shows that in this case self-heating of the tubular body at the sensor installation point
is negligible.
8. Electrical connection values / 9. Calculation examples ...