JUMO 902820 PROCESStemp RTD Temperature Probe for Process Technology (Also with ATEX Approval) Ex e Operating Manual - Manual (Page 8)

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The following temperature values must be taken into account for application in areas with a dust
explosion hazard:
Applicable to all zones:
The surface temperature of the equipment must not rise to a level that could ignite swirling dust or dust
deposits on the equipment. This is achieved through the following conditions:
No dust deposit
The surface temperature must not exceed
2
/
3
of the ignition temperature (in °C) for the corresponding dust-
air mixture.
With dust deposit
Surfaces on which a dangerous accumulation of smolderable dust cannot be prevented must not have a
temperature that is higher than 75 °C below the smoldering temperature of the dust concerned. If layers
thicker than 5 mm occur, a further reduction of the surface temperature must be applied.
Where a combination of swirling and deposited dust occurs, the lower of the values derived above must be
applied.
Note:
In this case, “surface” means the external surface of the equipment, see also EN 60079-14.
The ignition or smoldering temperature of the dust or dust-air mixture that is present must
be defined or determined by the operator of the plant or system!
400
300
200
100
0
0 10 20 30 40 50
Thickness of layer, in mm
Smoldering temperature
with a 5 mm thick layer
Max
im
u
m
p
e
rm
is
s
ibl
e
s
u
rf
a
c
e t
e
mp
era
tur
e
of
eq
u
ipm
e
n
t, in
°C
400 °C
T
5 mm
320 °C
T
5 mm
< 400 °C
250 °C
T
5 mm
< 320 °C
400 °C
320 °C
250 °C
Figure 2: Reduction of the maximum permissible surface temperature
with increasing thickness of the dust layer