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PFU 780 · Edition 02.12l
55
Flame control
7 Flame control
7 .1 With ionisation sensor
The PFU generates an alternating voltage (230 V AC)
between the sensing electrode and burner earth. The
flame rectifies this voltage. Only the DC signal (depen-
ding on the switch-off threshold for the pilot and main
burners) is recognised by the burner control unit as a
flame signal.
A flame cannot be simulated. Ignition and monitoring
with a single electrode is possible.
7 .2 With UV sensor
A UV tube inside the UV sensor detects the ultraviolet
light of a flame. It does not respond to sunlight, incan-
descent bulb light or infrared radiation emitted by hot
workpieces or red-hot furnace walls.
In the event of incident UV radiation the UV sensor rec-
tifies the supplied alternating voltage. As with ionisati-
on control, the burner control unit only detects this DC
signal.
When using UV sensors of Type UVS, the burner control
unit may be used for intermittent operation only. This
means that operation must be interrupted at least once
every 24 hours. This can be programmed using para-
meter 35.
For further information, see brochure UVS.
The burner control unit PFU..U is prepared for UV sensor
UVD 1. This enables continuous operation. For further
information, see Technical Information Bulletin UVD.
7 .3 Via the temperature in high temperature
equipment
High temperature equipment is defined as a thermo-
processing installation, in which the wall temperature of
the combustion chamber and/or the processing cham-
ber exceeds 750°C. Burner control unit PFU..D features
a special “High temperature operation” function. During
heating up, standard monitoring methods (ionisation or
UV) must be used for flame control. When the working
temperature has exceeded 750°C, indirect flame con-
trol can be taken over by a central monitoring device.
When the DI input (terminal 22a) is activated, the bur-
ner control unit reverts to this operating mode.
Important:
In “High temperature operation”, i.e. with
the DI input being activated, burner control unit PFU..D
does not evaluate the flame signal. The safety function
of the burner control unit’s flame control is deactivated
during this operating phase.