Air temperature affects the accuracy of an ultrasonic sensor. Ultrasonic sensors use the speed of sound to measure the time taken for an ultrasonic pulse to travel from the sensor, to the fluid level and back to the sensor. However, as the air temperature changes, the speed of sound changes, by 0.17% per degree Kelvin. Unless the sensor can compensate for this change of temperature, then as the temperature varies, so will the accuracy of the sensor.
Strong wind or air currents can cause unstable measurements. If your ultrasonic sensor is located in an exposed, outdoor environment or where significant air turbulance occurs, this needs to be considered in sensor selection. When wind speeds rise above the 30 - 38mph range they can cause unstable measurements with a loss of signal. The ultrasound can be scattered or deflected such that no echo that can be measured is received.
Turbulence or foaming on the fluid surface can reduce signal strength. Ultrasonic sensors rely on the liquid surface to reflect the ultrasound pulse to generate a signal the sensor can process. If, during emptying or filling of the vessel to be measured causes turbulence or foaming on the surface of the fluid, this will scatter the ultrasound to such an extent the echo is not strong enough to be usable and provide a measurement. This fault can also be caused by improper aiming, high dust or sticky build-up on the transducer face.
Mounting location can affect the function of the sensor. In a parabolic storage tank, if you place an ultrasonic sensor in the middle of the tank, you will encounter problems with secondary echoes. Also you cannot position the sensor too close to the side wall or you could get interference from ladder rungs or support braces. Awareness of where the fill stream is located is also required or this too will obstruct the ultrasound pulse.
The sound path must be perpendicular to the measured surface. To achieve a reliable signal the transducer must be installed perpendicular to the monitored surface. If you wish to fit the sensor in a standpipe or nozzle there are dimensional and design features that must be taken into account so the ultrasound pulse is compromised in its effectiveness.
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