The Siemens QRA53, QRA55, QRA71, and QRA75 flame detectors are ultraviolet (UV) flame sensors used for monitoring gas flames and yellow- or blue-burning oil flames in industrial combustion systems. These detectors identify the ultraviolet radiation emitted by the flame and transmit a signal to the burner management system confirming flame presence.

Unlike standard UV sensors designed only for intermittent operation, these detectors are suitable for continuous burner operation, meaning they can monitor flames in burners running for long periods without shutdown.

The sensors include a self-checking mechanism using a motor-driven shutter that periodically interrupts the UV signal to verify that the UV tube is functioning correctly and has not failed in a false flame condition. This safety feature is important in industrial burners that run continuously for more than 24 hours.

These flame detectors are widely used with Siemens burner control units such as LGK16, LGI16, LMV5, and LME75 series controllers, making them ideal for large industrial combustion systems including boilers, furnaces, and thermal process equipment.

The detectors operate in the UV spectral sensitivity range of approximately 190–270 nm, allowing them to detect real combustion flames while ignoring daylight and hot refractory surfaces inside the furnace.

Key Features

• UV flame detection technology for industrial burners

• Suitable for continuous burner operation

• Built-in self-checking shutter mechanism

• Detects gas flames and oil flames

• Reliable ignition spark proving

• High resistance to false flame signals

• Durable die-cast aluminum housing

• Long UV cell life for dependable monitoring

• Compatible with multiple Siemens burner control systems

Applications

• Industrial gas burners

• Industrial oil burners

• Dual-fuel combustion systems

• Steam boilers and hot water boilers

• Industrial furnaces

• Thermal oil heaters

• Process heating plants

• Power generation combustion systems

Why Choose Siemens QRA5x and QRA7x series flame detectors?

• Reliable Siemens combustion safety technology

• Designed for large industrial burner systems

• Continuous flame supervision capability

• Self-monitoring mechanism for higher safety

• Durable industrial design for harsh environments

• Compatible with Siemens burner management systems

Technical Description

The Siemens QRA5x and QRA7x series flame detectors use a UV-sensitive photocell that detects radiation produced by combustion flames in the 190–270 nm spectral range. When sufficient UV radiation reaches the sensor, it produces an electrical signal indicating flame presence.

For continuous burner operation, the detectors feature a motor-driven shutter mechanism that periodically blocks the UV radiation reaching the sensor. This creates a cyclic signal allowing the burner control system to verify that the detector is functioning correctly and preventing false flame detection due to UV cell failure.

The detectors are typically mounted on a burner viewing tube or flange, allowing the sensor to monitor the combustion flame directly inside the furnace or burner chamber. Their rugged construction and high protection rating allow them to operate reliably in demanding industrial environments.

Technical Specifications