Siemens Flame sensor QRB1A-A050B70A

The Siemens QRB1A-A050B70A is a flame sensor (photodetector) used for flame monitoring in diesel and heavy oil burners. It is designed for automatic combustion control systems and outputs a signal to the burner control. When flame is lost, the sensor triggers a quick fuel shut-off. The device is intended for use with Siemens burner controls and offers high sensitivity to flame radiation.

Replacement sensors are selected by matching the detection principle, spectral range, response time, cable length, connector type, and mounting sleeve to the existing burner control. Ensure the new unit fits the existing mounting arrangement and that cable and connector are compatible with the burner control. For oil flames, the spectral sensitivity must correspond to the flame type; for example, UV sensors are insensitive to hot refractory and daylight, reducing false signals. Consult the burner manual for the recommended sensor type.

Typical failure modes include a contaminated optical window that attenuates the signal, an aged sensing cell with weakened output, or a broken sheath causing intermittent signal loss. If the sensor does not detect flame within the safety time, the burner control initiates a lockout. Check the optical window for dirt and verify the wiring and sheath for continuity.