Optical Leak Detection Sensor: How Modern Sensors Improve Leak Detection

Leak detection is critical in industrial and commercial settings, particularly where liquids like water, oil, or chemicals can cause damage. Over the last few decades, technology has evolved from PTC thermistor sensors to advanced optical leak detection sensors, offering higher accuracy, longer lifespan, and fewer false alarms. In this article, we’ll explore what an optical leak detection sensor is, how it works, and why it has become the preferred choice for modern leak monitoring.

A Brief History of Leak Detection Sensors

Introduction of PTC Thermistor Sensors

In the early 1990s, PTC (Positive Temperature Coefficient) thermistor sensors were widely used for leak detection in industrial applications. These PTC thermistors are resistors that increase resistance with rising temperature, making them suitable for temperature-sensitive monitoring.

How they worked:

• A small voltage was applied to heat the thermistor to a set temperature (typically 60–120°C).
• The sensor’s current draw was continuously monitored by an alarm panel.
• When a leak occurred, the liquid contacted the heated thermistor, cooling it and causing a resistance drop.
• The sensor drew more current to maintain its temperature, triggering an alarm in the detection system.

While effective for the time, these sensors had limitations:

• Sensitivity to ambient temperature fluctuations could trigger false alarms.
• Continuous high-temperature operation reduced sensor lifespan.
• Small leaks could sometimes go undetected.

While effective for the time, these sensors had limitations:

Small leaks could sometimes go undetected.Leak Detection Mechanism:

Sensitivity to ambient temperature fluctuations could trigger false alarms.

Continuous high-temperature operation reduced sensor lifespan.

• The sensor would be monitored by an alarm unit that continuously checked the current being pulled by the thermistor. In normal conditions, the current remained steady, indicating that the sensor was maintaining its set temperature.
• When a leak occurred, the leaked fluid, usually water, would come into contact with the heated thermistor. The heat from the thermistor would cause the water to evaporate.
• As the water evaporated, the temperature of the thermistor would drop due to the cooling effect of the evaporating fluid.

Response to Temperature Drop:

• A decrease in temperature would cause the thermistor’s resistance to drop. To maintain its operating temperature, the sensor would then draw more current.
• This increase in current would be detected by the leak detection panel, as it would be calibrated to recognise such changes.
• Upon detecting the increased current, the leak detection system would trigger an alarm, alerting operating staff to the presence of a leak.

Development of Optical Leak Detection Sensors

Modern leak detection has largely shifted to optical leak detection sensors, which use light rather than heat to detect liquids. Optical sensors have several advantages:

• No moving parts, increasing durability and lifespan.
• High accuracy with reduced false alarms.
• Can detect a wide range of liquids, including non-conductive fluids like oil and diesel.

Spot probes have improved drastically over the last twenty years, and modern sensors now use an optical sensor to detect leaks. An optical liquid leak detection sensor contains an infrared light emitting diode and a phototransistor. This type of sensor also has the advantage of not having any moving parts, increasing the life expectancy of the probe.

Examples of these modern sensors include our optical leak sensor type OSP – engineered to detect leaks of various liquids. There is also the Type OSPW, which is adapted to detect non-conductive liquid leaks (like diesel or oil).

Optical Sensor in the air

An optical leak detection sensor contains an infrared LED and a phototransistor. The LED emits light that undergoes total internal reflection within a prism tip. In air, most of the light is reflected back to the phototransistor, producing a strong signal.

Optical Sensor in liquid

When the prism tip is submerged in liquid, the refractive index changes at the interface. Light scatters instead of reflecting fully, reducing the signal received by the phototransistor. This drop in output indicates the presence of a liquid, triggering an alarm in the detection panel.

This method allows optical sensors to detect even small leaks quickly and reliably, without relying on temperature changes like thermistor sensors.

Advantages of Optical Leak Detection Sensors

1. Durability: No moving parts, minimal maintenance, and longer lifespan compared to PTC thermistor sensors.
2. Accuracy: Detects a wide variety of liquids with reduced false alarms.
3. Rapid Response: Quickly identifies leaks, enabling faster interventions.
4. Versatility: Suitable for water, oil, diesel, and other non-conductive liquids.
5. Integration: Can connect with advanced alarm panels for real-time monitoring in industrial systems.

Applications

Optical leak detection sensors are widely used across industries:

• Industrial Plants: Monitor chemical, water, or oil lines.
• Oil & Gas Facilities: Detect oil leaks quickly to prevent environmental hazards.
• Data Centres & Laboratories: Protect sensitive equipment from water or coolant leaks.
• Manufacturing Sites: Ensure production lines remain leak-free to avoid downtime.

Conclusion

PTC thermistor sensors were the foundation of leak detection technology, but their limitations have made them largely obsolete. Optical leak detection sensors have revolutionised the industry with higher accuracy, reliability, and longer lifespan.

For industrial and commercial environments where leak detection is critical, understanding what an optical leak detection sensor is and how it works is essential. Modern ODS systems, like the ODS4-3 Alarm Panel with optical sensors, offer a proactive solution to prevent costly damage and maintain operational safety.