Photoresistive Flame Detectors Qrb1 / Qrb3 - Siemens LMV37.4 Series Basic Documentation

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4.4.3 Photoresistive flame detectors QRB1 / QRB3

No-load voltage at QRB1/QRB3 terminal
(X10-05 pin 3)
Max. perm. length of QRB1/QRB3
detector
cable (laid separately)
Note
A detector resistance of RF <500  is identified as a short-circuit and leads to safety
shutdown in operation as if the flame had been lost.
For this reason, before considering the use of a highly sensitive photoresistive detector
(QRB1B or QRB3S), it should be checked whether this type of flame detector is indeed
required! Increased line capacitance between QRB1/QRB3 connection and mains live
wire L has an adverse effect on the sensitivity and increases the risk of damaged flame
detectors due to overvoltage. Always run detector cables separately!
Threshold values when flame is supervised by QRB1/QRB3:
Start prevention (extraneous light)
with R
QRB
Operation with R
QRB
Short-circuit detection with R
0,1 1
Figure 8: QRB1/QRB3 input at AC 230 V
A flame detector resistance of RF <500 Ω is identified as a short-circuit and leads to
safety shutdown in operation, like in the case of loss of flame.
Basic documentation LMV37.4...
4 Technical Data
Approx. DC 5 V
3 m (wire – wire 100 pF/m)
<400 k
Intensity of flame ≥10%
<230 k
Intensity of flame >16%
<0.5 k
QRB
10 100 1000
CC1P7546en
17.12.2018