VCAS Ultrasonic Sensors

Ultrasonic sensors emit short, high-frequency sound pulses at regular intervals. These propagate in the air at the velocity of sound. If they strike an object, then they are reflected back as echo signals to the sensor, which itself computes the distance to the target based on the time-span between emitting the signal and receiving the echo. As the distance to an object is determined by measuring the time of flight and not by the intensity of the sound, ultrasonic sensors are excellent at suppressing background interference. Virtually all materials which reflect sound can be detected, regardless of their colour. Even transparent materials or thin foils represent no problem for an ultrasonic sensor. VCAS ultrasonic sensors are suitable for target distances from 60 mm to 10 m and as they measure the time of flight they can ascertain a measurement with pinpoint accuracy. The sensors can even resolve the signal to an accuracy of less than 0.18 mm. VCAS Ultrasonic sensors can see through dust-laden air and ink mists. Even thin deposits on the sensor membrane do not impair its function.

Accuracy - Resolution 0.18mm, Response Time 240ms
The (absolute) accuracy is the discrepancy between the real distance between sensor and object and the distance as measured by the sensor. The accuracy obtainable depends on the reflective properties of the object and the physical influences affecting the velocity of sound in air. Objects with poor reflective properties or a surface roughness greater than the wavelength of the ultrasonic frequency have an adverse effect on the accuracy achievable. It is not possible to quantify this exactly but as a rule of thumb we can assume an inaccuracy of several wavelengths of the ultrasonic frequency employed.

Air temperature =<2%
The biggest influence on the velocity of sound and hence on the accuracy is the temperature of the air (0.17%/K). Therefore, the VCAS ultrasonic sensors contain temperature compensation circuitry. An accuracy =<2% is possible with our temperature-compensated sensors.

Air pressure
The velocity of sound over a wide range does not depend on the pressure of the air.

Relative humidity
In comparison to the influence of temperature, the effect of the humidity of the air on the accuracy can be ignored.

Repeat accuracy R ±0.15%
The repeat accuracy, or reproducibility, describes the deviation in the measured distances under the same conditions over a defined period. The repeat accuracy of VCAS sensors is better than ±0.15%.

VCAS UltraSonic Sensor Specifications

The detection zones of VCAS ultrasonic sensors

On the other hand, a reflector with better reflective properties will be detected in a zone with a size somewhere between that of the red and blue areas. A sensor's blind zone determines its smallest permissible detection range. No objects or disturbing reflectors should be placed in the blind zone because this can lead to incorrect measurements.