A flame sensor is a type of sensor that is highly sensitive to regular light, making it ideal for use in flame detection systems. It can detect fire or light with wavelengths in the range of 760 nm to 1100 nm. Due to its sensitivity to high temperatures, the sensor should be installed at a safe distance from the flame source. It is capable of detecting fire from up to 100 cm away, with a sensing angle of 60°. The sensor provides either an analog or digital output signal. Flame sensors are commonly used in fire-fighting robots and fire alarm systems for early fire detection.

What Is a Flame Sensor?

A flame sensor is a type of detector specifically designed to detect and respond to the presence of a flame or fire. The way it reacts depends on how it's integrated into a system, which may include alarms, natural gas or propane lines, and fire suppression systems. One common use for flame sensors is in industrial boilers, where they serve a critical role in confirming that the boiler is functioning correctly. Compared to traditional heat or smoke detectors, flame sensors offer faster and more accurate detection thanks to their flame-sensing technology.

How a Flame Sensor Works

Flame sensors typically consist of an electronic circuit paired with a receiver that detects electromagnetic radiation. Many flame sensors use the infrared flame flicker method, which enables them to detect flames even when obscured by oil, dust, water vapor, or ice. This makes them highly reliable in challenging industrial environments.

Flame Sensor Module Overview

The flame sensor module comes with a 4-pin configuration, as outlined below. When used with a microcontroller, each pin serves the following purpose:

• Pin 1 (VCC): Power supply input, operating voltage between 3.3V and 5.3V
• Pin 2 (GND): Ground connection
• Pin 3 (AOUT): Analog output signal (connected to MCU I/O pin)
• Pin 4 (DOUT): Digital output signal (connected to MCU I/O pin)

Types of Flame Sensors

Flame sensors are commonly categorized into the following four types based on their detection technology:

1. IR Single-Frequency Flame Detectors
2. IR Multi-Spectrum Flame Detectors
3. UV Flame Detectors
4. UV/IR Combined Flame Detectors

Each type is designed to detect different characteristics of flame emissions, making them suitable for specific applications and environments.

Features & Specifications

Key features of the flame sensor module include:

• High photosensitivity for reliable flame detection
• Fast response time, enabling quick detection
• Easy to use and integrate with microcontroller systems
• Adjustable sensitivity to suit different environments
• Detection angle: 60°
• Capable of detecting within a specific flame range
• Adjustable accuracy for fine-tuned performance
• Operating voltage: 3.3V to 5V
• Supports both analog and digital outputs
• Compact PCB size: 3 cm × 1.6 cm
• Built-in power indicator and digital output indicator LEDs

Detection Note:

The module can trigger flame detection at distances up to 0.8 meters under low flame intensity. With stronger flame intensity, the detection range can be extended even further.

Applications

Flame sensors are widely used in high-risk environments where early flame detection is critical. Common applications include:

• Hydrogen refueling stations
• Industrial heating systems
• Fire detection and alarm systems
• Fire-fighting robots
• Drying equipment and systems
• Industrial gas turbines
• Residential heating systems
• Gas-powered kitchen appliances

Summary

In summary, flame sensors play a vital role in minimizing fire-related risks by providing fast and accurate flame detection. Compared to traditional smoke or heat detectors, they respond more quickly, enhancing overall safety in both industrial and domestic settings.

Flame Sensor FAQ

What happens when a flame sensor goes bad?

A common symptom of a faulty flame sensor is short cycling — the furnace turns on briefly and then shuts off. This happens because the sensor fails to detect the flame, so as a safety precaution, it shuts off the gas valve. Although the flame is actually present, the lack of gas causes it to extinguish.

What does a flame sensor do?

A flame sensor is a safety device used in gas-powered heating systems. Its job is to ensure that the gas valve only remains open when a flame is present, preventing unburned gas from accumulating and creating a safety hazard.

How does a flame sensor work?

Most flame sensors use infrared detection to sense the unique radiation emitted by flames. When a flame is detected, the sensor generates an electrical signal, which is then processed by the system to either continue operation, trigger an alarm, or activate a fire suppression system.

What’s the difference between a flame sensor and a thermocouple?

• A thermocouple is used in older systems with standing pilot lights. It senses whether the pilot flame is lit.
• A flame sensor, on the other hand, is used in modern furnaces to detect that the main burners have ignited properly after gas is released.

How can I tell if my flame sensor needs replacing?

Look for yellow burner flames — this can indicate improper combustion, possibly due to a faulty flame sensor. If the furnace frequently shuts off shortly after starting, or fails to ignite consistently, the sensor might be to blame.

What causes a flame sensor to fail?

The most common cause is dirt or soot buildup on the sensor. Over time, contaminants can coat the sensor, making it unable to accurately detect the flame. This can lead to ignition failure or shutdowns during operation.

Will a furnace run without a flame sensor?

No. The flame sensor is a critical safety component. Without it, the furnace cannot operate because it has no way to verify safe combustion.

Can the flame sensor be cleaned or does it need to be replaced?

In many cases, a flame sensor can be cleaned using fine sandpaper or steel wool to remove residue. However, if cleaning doesn’t solve the issue, replacement may be necessary.

How do I stop a flame or fire sensor alarm from going off?

If a flame or fire sensor is triggering a false alarm, press the “Hush” or “Test” button (usually located on the alarm). This will silence the alert for about 8 minutes, provided smoke or heat levels have dropped. If not, the alarm will continue until the hazard is cleared.

Does the pilot flame need to touch the thermocouple?

Yes. For a thermocouple to function properly, the pilot flame must be in direct contact with it. If the flame doesn’t touch it—possibly due to misalignment or a bent probe—the system may shut down.

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