The blind spot of an ultrasonic level gauge is similar to the blind spot in human vision. When an object is too close to the eye and at a fixed angle, it becomes unclear or invisible—this area is known as the blind zone. In the case of ultrasonic level gauges, this blind zone refers to the area near the sensor where accurate measurements cannot be made.
Ultrasonic level gauges operate by emitting sound waves and measuring the time it takes for them to reflect back from the surface of the liquid or material. The speed of sound in air is constant, so the time between emission and reception of the echo directly corresponds to the distance. Since the sound wave travels both ways (down to the surface and back), the actual distance is half of what is measured. By knowing the total height of the tank or container, the liquid level can be calculated by subtracting the measured distance from the total height. This method allows for precise and non-contact level measurement.
The size of the blind zone varies depending on the range of the device. For short-range models, the blind zone is smaller, while long-range models have a larger blind zone. Typically, the blind zone ranges from 30 cm to 50 cm. However, in certain applications where space is limited, a smaller blind zone is necessary. In such cases, specialized ultrasonic level gauges with reduced dead zones—often just 4 to 6 cm—are available. These models, though, have a shorter measurement range, usually up to 0.6 meters.
When the liquid level enters the blind zone, the gauge may display a reading corresponding to a secondary echo. For example, if the blind zone is 0.3 meters and the actual liquid level is only 0.2 meters above the sensor, the gauge might show a value based on a 0.4-meter distance. This happens because the sound pulse reflects off the liquid surface, then again off the transducer before being received. If the reflection conditions are good, multiple echoes may occur, leading to potential inaccuracies in readings.
Proper installation is crucial to avoid interference from the blind zone. Understanding the characteristics of the blind zone helps ensure more reliable and accurate measurements in various industrial and commercial settings.
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