Evaluating a laser rangefinder extends beyond extinction ratio

Limits of Extinction Ratio

Extinction ratio, once a key parameter in LRF performance assessment, has lost some of its importance in today’s context. While it measures how much attenuation the system can handle before it stops measuring, modern software and other factors now heavily influence measurement optimization. However, digging deeper into conditions of extinction ratio tests it exposes their limitations to assess performance under real measuring situations in the real-world.

Limits of Extinction Ratio Tests
The limitations of extinction ratio tests become evident when other crucial performance parameters like beam divergence, target size or target speeds are considered. Extinction Ratio Tests are typically conducted over short distances up to max. 500 m on a beam-sized target. However, if we were to apply these conditions to a measurement 10 km away for an LRF with a 2 mrad divergence, it would demand a target with a diameter of 20 m – an unrealistic size for field conditions. In contrast, our LRF 7047, with a 0.5 mrad divergence, results in a target diameter of only 5 m at 10 km. This highlights that in practical scenarios, the significance of the extinction ratio diminishes compared to the importance of divergence.

In addition also the use of software algorithms in multi-pulse lasers for performance enhancement is not reflected in these extinction ratio tests at a range of only up to 500 m. During measurements on short range, the transmitter (Tx) of our multi-pulse LRFs automatically adjusts to the current measurement conditions (and to the short range) and it reduces its output to prevent any saturation or damage to the receiver of the LRF. Furthermore our LRFs are optimized via software to suppress wrong measurements because of particles in the air, such as dust. In specific test conditions this might appear like a decreased extinction ratio result as the laser rangefinder is not demonstrating any more its full potential, which is normally used for measuring long distances. To determine extinction ratio for our modules, a distance above 500 m and a special software setting is required.

Therefore, this underlines the importance of optimizing LRFs comprehensively for real-world long-range measurements rather than solely focusing on just one parameter. 

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