Overview
Ultrasonic sensors play an important role in industrial automation. Like many sensors, their performance is affected by external factors. This article examines how ultrasonic sensors address challenges from environmental conditions such as temperature and humidity, and which external factors should be considered to ensure reliable detection.
Q1: Do temperature and humidity affect detection range?
Ambient air temperature and humidity influence the detection range of ultrasonic sensors. In general, higher temperature and higher humidity tend to reduce detection distance. This attenuation is not linear and varies between sensor models.
Q2: Are measurements affected by dust, rain, or fog?
Heavy dust, heavy rain, or heavy snow can weaken sound energy, narrow the sound cone, and reduce the sensor's maximum detection distance. Small amounts of dust and dirt on the transducer surface typically do not affect detection. Appropriate protective measures, such as protective covers, can prevent rain, snow, or frost from accumulating on the transducer.
Q3: Which environmental factors affect ultrasonic measurements?
1. Air temperature
Air temperature has a significant effect on measurement accuracy. After an echo is detected, the sensor calculates the distance to the target using the speed of sound. The speed of sound changes by approximately 0.17% per kelvin. To compensate for temperature effects, many ultrasonic sensors from manufacturers such as Pepperl+Fuchs include a temperature probe. The probe measures ambient temperature and the sensor corrects for temperature-related drift, a feature known as temperature compensation.
Some sensors are designed for low-temperature applications, for example in cold storage for the food industry, and can operate in a range from -25 °C to +70 °C with compensation for low-temperature measurement errors.
2. Humidity
At room temperature or lower, the effect of humidity on the speed of sound is negligible. At higher temperatures, the speed of sound increases with increasing humidity.
3. Air pressure
Between sea level and 3000 meters altitude, the speed of sound decreases by less than 1%. At a fixed location, normal atmospheric fluctuations are negligible and their effect on the speed of sound is essentially immeasurable.
4. Airflow
If the target has standard reflective properties, normal airflow (wind) up to about 50–61.5 km/h does not affect ultrasonic detection. Severe storms or hurricanes can cause unstable detection or signal loss. For example, high-temperature objects such as glowing metal can create strong atmospheric turbulence that scatters or refracts ultrasonic waves, preventing a detectable echo from returning.
5. Paint spray
The impact of atomized paint on ultrasonic sensor performance is hard to quantify. However, if paint mist deposits on the transducer surface, it can reduce transducer sensitivity.
6. Ambient noise
Ambient noise is usually distinguishable from the target echo and generally does not cause faults. If an interfering source operates at the same frequency as the ultrasonic sensor, ambient noise can affect target detection. An example is filling a bin with stones, where mechanical noise may interfere with detection.
Q4: Do ultrasonic sensors need cleaning or maintenance?
To some extent, ultrasonic transducers self-clean through vibration. If necessary, deposits related to the application can be removed with a soft cloth and water. Thin films, such as a light oil layer, typically do not affect sensor function and do not need to be removed.
