Li You'an, Guoke Hanhai Laser Technology (Beijing) Co., Ltd.

Chemical detectors and optical detectors are two distinct types of gas detection devices. Chemical detectors are basically point detectors, while optical detectors are mostly telemetry-based. Optical (laser) telemetry gas detectors utilize Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology, which measures target gases using specific wavelengths emitted by semiconductor lasers. Telemetry systems detect the overall concentration of gas plumes formed by leaks, whereas point detectors measure gas concentration at the exact location where the device is installed. Under the same leak conditions, laser telemetry gas detectors offer significantly higher detection efficiency, greater sensitivity in measurement values, earlier leak detection, and a higher overall leak detection rate compared to point detectors.

PART.1 Introduction to Detection Efficiency of Flammable Gas Detectors

Detection efficiency is a fundamental performance indicator for gas detectors. It is generally evaluated based on three key aspects: detection distance, response time, and stability of measured gas concentration values. This indicator determines the ability to detect gas leaks when they occur.

PART.2 Comparative Analysis of Detection Efficiency: Telemetry vs. Point Gas Detectors

1. Laser telemetry offers much longer detection distance than point gas detectors

Laser telemetry systems can detect gas leaks at distances ranging from tens to hundreds of meters, focusing on the overall concentration of the leaking gas plume. Their performance is unaffected by the distance between the device and the leak source. In contrast, point detectors only measure gas concentration at their installation location, making them highly sensitive to the distance between the leak point and the detector. For leaks far from the installation site, point detectors are often ineffective or even unable to detect the leak.

2. Laser telemetry has faster response time than point gas detectors

Since laser telemetry measures the concentration of the entire gas plume, it is not affected by the gas diffusion speed or plume size. Leaks can be detected immediately once they occur, with the total concentration value measured directly. Point detectors, however, have response times influenced by gas diffusion speed, distance from the leak point, wind direction, and wind speed. These external factors make their detection time, stability, and overall performance uncontrollable.

3. Laser telemetry provides more stable gas concentration measurements than point detectors

Telemetry devices measure the integral concentration of the entire gas plume, with readings only related to the leak concentration and plume size. They can quickly detect diffusing gas plumes, resulting in extremely high detection rates. Point detectors, by contrast, only measure concentration at a single point and cannot reflect the actual leak volume. For accurate detection, leaking gas must diffuse to the detector's location and remain there continuously for a certain period (typically 30 seconds) to ensure stable gas entry into the device.

Experimental simulations using 100% methane (simulating natural gas leaks) showed that point detectors initially read 0.02%, which increased to 0.57% after 30 seconds as gas accumulated. When the gas release point was moved 35 cm horizontally away, the readings dropped sharply—even to zero in some cases. This experiment confirms that minor changes in external conditions can destabilize point detector readings, making stable alarms difficult to achieve.

(1) Experimental data: Detection distance and response time (indoor environment)

(2) Experimental data: Stability of measured concentration (indoor environment)

PART.3 Conclusions

1.By measuring the integral concentration of gas plumes, telemetry gas detectors can detect leaks within long distances (e.g., 100 meters). As long as a gas plume exists within this range, the telemetry device can quickly detect it with stable readings. These devices monitor concentration changes across the entire surveillance area, offering high sensitivity.

2.Point flammable gas detectors measure concentration only at their installation location. In real leak scenarios, their detection time and concentration readings are easily affected by external factors such as distance from the leak, leak volume, and meteorological conditions. This leads to unstable readings or even failure to detect leaks, resulting in lower sensitivity. In practical applications, point detectors are suitable for short-distance, multi-point installation. Achieving stable alarm concentrations requires increasing detector density and ensuring prolonged gas leaks, making them more suitable for indoor enclosed spaces rather than outdoor open areas.

3.Experimental results confirm that in outdoor environments, laser telemetry gas detectors do not experience significant reading fluctuations due to environmental complexity. Point detectors, however, may show sharp signal attenuation or complete failure to detect leaks. Under the same conditions, laser telemetry gas detectors outperform point detectors in overall detection efficiency.