JUMO 902820 PROCESStemp RTD Temperature Probe for Process Technology (Also with ATEX Approval) Ex e Operating Manual - Manual (Page 6)

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Example 1
A thermometer is to be used in temperature class T4 (maximum temperature 135 °C, safety reduction of the
limit: 5 °C).
Thermowell constant SK = 80 °C/W
Maximum power in the circuit P = 0.5 W
TS = 130 °C – 0.5 W × 80 °C/W
TS = 130 °C – 40 °C = 90 °C
So the maximum temperature (the temperature of the medium being measured) on the probe tip must not
exceed 90 °C, since in the event of a fault it is possible that the limit for the temperature class will be
exceeded. DANGER OF EXPLOSION!
Example 2
The same thermometer is to be used in the same application as above, but this time using the JUMO
dTRANS T01 transmitter, which has a considerably lower maximum power, this permitting a substantial
increase of the maximum temperature being measured, and so a wider range of applications.
Thermowell constant SK = 80 °C/W
Maximum power in the circuit P = 0.011 W (JUMO transmitter, type 707015)
TS = 130 °C – 0.011 W × 80 °C/W
TS = 130 °C – 0.88 °C = 129.12 °C
So the maximum temperature (the temperature of the medium being measured) on the probe tip must not
exceed 129.12 °C, since in the event of a fault it is possible that the limit for the temperature class will be
exceeded. DANGER OF EXPLOSION!
If a transmitter is to be used in a thermometer that has a terminal head, then the permissible operating limits
for the transmitter must also be taken into account. The transmitter is hermetically sealed into the terminal
head. The ambient temperature and the heat conducted through the protective fittings from the medium
being measured as well as the self-heating of the transmitter all contribute to a rise in surface temperature
and the temperature within the terminal head.
The self-heating and heat conduction from outside, via the protective fittings, have been determined for the
worst case of a measured temperature of 300 °C and the maximum power dissipation of the transmitter of
750 mW. In such a situation, the temperature of the terminal head is 18 °C higher than the ambient
temperature.
It is necessary to take account of the ambient temperature conditions prevailing in the application, and to
check that the transmitter is being operated within its specifications and thus does not itself constitute an
explosion hazard.
The values specified in the type test certificate for the transmitter that is used must be observed and adhered
to.
Example: transmitter
Temperature measurement in class T4 max. 135 °C, ambient temperature of the terminal head 40 °C,
temperature rise in head 18 °C. The resulting max. temperature in the terminal head is 40 °C + 18 °C = 58
°C. The transmitter used is a JUMO dTRANS T01 according to data sheet 707010 in “II1G”, and its
maximum permissible ambient temperature when used in class T4 is 60 °C. Since 58 °C < 60 °C, this
transmitter can be operated inside the terminal head for temperature class T4 in the surrounding area.
5.2 General information on the types of protection
When using different protection types, the self-heating behavior of the equipment to EN 60079-0 must
generally also be specified, for classification in the appropriate temperature class.
5.3 Flameproof enclosure, Ex “d” protection
The components that could ignite a potentially explosive atmosphere are arranged within a flameproof
enclosure (here: terminal head with cable gland) that is capable of containing the internal pressure caused
by an explosion of an explosive mixture inside, and prevents the explosion from being propagated to the
potentially explosive atmosphere surrounding the enclosure. The underlying principle is safe containment in
the event of an explosion.
It is not mandatory to connect the versions in a flameproof enclosure to intrinsically safe circuits, however, it
must always be ensured that the rise in temperature of the thermometer remains limited, as was described in
detail in Section 5.1. and demonstrated by case studies.