58
Flame Monitor
Sensor Current Measurement
Flame monitor with UV sensor
The UV radiation of hot flame gases is
utilized for generating the flame signal.
The radiation detector used is a UV-
sensitive tube with two electrodes and
being live all the time. This UV tube will
ignite when subject to light from the
190-270 nm range of the spectrum and
thus cause a current to flow to the flame
signal amplifier.
The UV tube will not respond to the
after-glowing refractory lining of the fur-
nace, sunlight, daylight or light of the
boiler room lighting system.
The service life of the UV tube is about
10,000 hours at ambient temperatures
up to 50°C; higher ambient tempera-
tures will considerably reduce its ser-
vice life.
Burners operated continuously or inter-
mittently for more than 24 hours without
interruption (e.g. boiler sequence con-
trol) or burners operated on steam boi-
lers must be equipped with the
automatic furnace controller of type
LGK 16... and its associated self-con-
trolling flame monitoring circuit (QRA
5...).
For data and design instructions refer to
automatic furnace controller:
LFL 1...
No. 7451 D
LGK 16...
No. 7785 D
Sensor currents
* See technical data for automatic
furnace controller LFL 1 / LGK 16...
** See data on unit KF 8832 for sensor
current measurement.
UV current measurement with QRA 5
For an accurate UV current measure-
ment it is recommended to make use of
the
tester KF 8832
. If a normal meter
(microammeter) is used for UV current
measurement it is advisable to make
the measurement as shown in the
figure. For this, a capacitor
C = 470
μ
F, 15V (or with higher electric
strength) must be integrated in the
measuring circuit.
Meter: 100
μ
A/Ri = 3 k
Ω
Connect the meter between the auto-
matic furnace controller and the UV
flame sensor QRA 5... (terminal 22 (-)
and 5 (+)).
Take care to observe the right pola-
rity.
Alignment of the UV sensor QRA 5...
The mounting flange is movable sup-
ported on the sensor tube to allow the
exact alignment of the sensor window
relative to the direction of incidence of
the UV radiation.
NOTE:
The terminal (22) must be con-
nected to earth all the time.
Cleaning the sensor
Check the UV sensor window for possi-
ble accumulation of dirt at regular inter-
vals and clean if required. Take care the
sensor window is free of dust all the
time.
If upon cleaning the sensor does not
properly work it will be required to
replace it by a new one.
Automatic
controller
Minimum
required
Maxi-
mum
possible
Monitor
with UV
with UV
* LFL 1...
70
μ
A
630
μ
A
* LGK 16...
**
**
Recommended instrument range:
UV monitor 0 - 1000
μ
A
Autom. furnace controller LFL 1...
UV sensor with QRA 2...
Autom. furnace controller LGK 16...
UV Sensor with QRA 5...