PFU 780 · Edition 02.12
54
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 (depending 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, incandescent bulb
light or infrared radiation emitted by hot workpieces or red-
hot furnace walls.
In the event of incident UV radiation the UV sensor rectifies
the supplied alternating voltage. As with ionisation 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 parameter 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 thermoprocessing
installation, in which the wall temperature of the combustion
chamber and/or the processing chamber 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 control can be taken over by a central monitoring device.
When the DI input (terminal 22a) is activated, the burner 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 eva-
luate the flame signal. The safety function of the burner control
unit’s flame control is deactivated during this operating phase.