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Ultrasonic Sensors

Ultrasonic sensors are designed for contactless and wear-free detection of a variety of targets by means of sonic waves. It is not important whether the target is transparent or coloured, metallic or non-metallic, firm, liquid or powdery. Environmental conditions such as spray, dust or rain seldom  affect their function.

Sensing modes Ultrasonic sensors are mainly used in the diffuse mode. An object in front of the sensor is detected by its reflection of a part of the emitted sound wave. It is also possible to use ultrasonic sensors in the opposed and reflective mode. An ultrasonic opposed mode sensor consists of an emitter and a receiver which “listen” to each other permanently. The ultrasonic sound is interrupted by an object between the emitter and receiver and the sensor generates a switching signal.

Beam Angles: M18/M30 (threaded metal barrel) and Q30 sensors (rectangular plastic housing) have a very narrow sonic angle of approx. 6° and are especially suited for precise detection of relatively small targets. The concentration of the sonic beam provides sensing ranges of up to 8 m. The sonic cones of our Q45U and T30U sensors are between 12 and 15°. The sensor type CP40 (rectangular plastic housing) has a much wider sonic cone (60°). These devices are suited to monitor a large area and to detect smooth, flat and even tilted objects.

Adjustments With almost all ultrasonic sensors it is possible to adjust the lower and the upper limit of the switching or measuring range. Objects outside this range may be detected, but they don’t initiate the output to change state. Q45U sensors are equipped with DIP switches for adjustment of several parameters such as the sensor’s response time, it’s performance during a loss of the echo, or in case of direct operation of a pump in conjunction with the sensor.

Repeat accuracy Among other factors such as the wave length, the accuracy of ultrasonic sensors is mainly limited by speed fluctuations of the sound during temperature changes. Therefore some of the sensors feature temperature compensation. This enables analogue Q45U sensors to achieve a repeat accuracy of up to 0.6 mm over a wide temperature range.

Output functions:  Ultrasonic sensors with switching output are available in all housing types. M30, T30U and T50U type sensors also come with two switching outputs (e.g. for minimum and maximum level control). Versions with an analogue current or voltage output are included in most housing styles.

Noise suppression:  Noise such as metal "clink" or pressure "hammering" do not influence the evaluation due to optimised selection possibilities of the frequency range and the patented noise suppression circuitry.

Synchronisation:  In most cases, sensor synchronisation will prevent mutual interferences. Most sensors of the series RUC...M30, RU...M18 and RU...Q30 are capable of self-synchronisation by simply connecting the synchronisation line. Synchronised sensors emit sonic pulses simultaneously. When mounted correctly, they perform like a single sensor with an extended detection angle.



Range: 500mm
Output: Switch (pnp or npn)
Mode: Diffuse or Retroflective
Adjustment: Teach


Range: 1 m
Output: Switch (pnp) or Analogue (4-20mA)
Mode: Diffuse or Retroflective
Adjustment: Pot or Program or Teach


Range: 6 m
Output: Switch (pnp or 2x pnp) or Analogue (4-20mA)
Mode: Diffuse
Adjustment: Pot or Program


Range: 2 m
Output: Switch (pnp or npn) Analogue (4-20ma/0-10V)
Mode: Diffuse
Adjustment: Teach


Range:  1 m
Output: Switch (pnp) or Analogue (0-10V)
Mode: Diffuse
Adjustment: Pot


Range: U = 3 m, UR = 250 mm
Output: Switch (pnp or npn) or Analogue (4-20mA/0-10V)
Mode: Diffuse
Adjustment: Teach


Range:  8 m
Output: Switch (pnp or npn) or Analogue (4-20mA/0-10V)
Mode: Diffuse
Adjustment: Teach


Range:  1.8 m
Output: Switch (pnp) or Analogue (4-20mA/0-10V)
Mode: Diffuse
Adjustment: Pot


Range: 1.5 m
Output: Switch (pnp)
Mode: Opposed
Adjustment: Connection


Range:  600 mm
Output: Switch (pnp)
Mode: Opposed
Adjustment: Connection

Programming Interface

"Teach" Adapter




Sensing conditions
The ultrasonic transducers are especially optimised for the medium "air". The sensors can also be used for other gaseous media but then they require a sensitivity adjustment.

Blind zone
Diffuse mode ultrasonic sensors are not capable of detecting targets which are located directly in front of the sonic transducer. The area between the sonic transducer surface and the beginning of the detection range is called blind zone and must always be kept free.

Air temperature and humidity
Both air temperature and air humidity influence the sonic pulse duration. An air temperature increase of 20 °C leads to a change of the sensing distance of up to +3.5 % when using the M30 or the Q30 version (resp. +8 % with the CP40-sensor), whereas the distance of the object seems to decrease. An increase of humidity results in an increase of the sound speed of max. 2 % as opposed to dry air conditions.

Air pressure
Normal atmospheric changes of ± 5 % (for a local reference point) can lead to a deviation of the sensing range of about ± 0.6 %.

Air streams
Air streams influence the echo time, however, air flow speeds of up to 10 m/s are insignificant. In conditions where turbulences prevail, e.g. above glowing metal, the use of ultrasonic sensors is not recommended, because the echo of distorted sound waves is difficult to evaluate.
Environmental conditions
Normal concentrations of rain or snow do not affect the sensor but direct wetting of the transducers should be avoided. The transducer types CP40 are not protected against humidity (degree of protection IP40). All other ultrasonic sensors are not damaged by water but correct functionality may be impaired. Therefore, the ultrasonic transducers should generally not be subjected to direct wetting.

Solid, fluid, granular and powdery targets can be detected by the ultrasonic sensor. The surface variation of the object should not exceed 0.15 mm. Larger variations may lead to a reduction of the sensing range. However, such targets do not require exact alignment. The target colour has no influence on the sensing distance, also transparent targets like glass or clean plastic are reliably detected. The temperature of the target influences the sensing range: hot surfaces reflect the sonic beam wave less than cold ones. The ultrasonic reflectivity of liquid surfaces is the same as that of solid, flat objects. Correct alignment should observed. Textiles, foams, wool, etc. absorb the sonic wave. The sensing range will be reduced. Simultaneous operation of multiple sensors When multiple ultrasonic sensors are used, mutual interference of the sound cones may arise. Here, either sensor synchronisation, alternate sensor operation, or a minimum distance between the sensors will solve this problem.

Synchronisation of ultrasonic sensors causes the sensors to emit the sonic pulse simultaneously. Using the series RUC…- M30, RU…-Q30 und RU…-M18 enables synchronisation of sensors by connecting the X1-line. Selecting the synchronisation mode to avoid mutual interferences is only recommended for applications where the sensors are mounted closely to each other and emit in approx. the same direction. In this mode, the sensors perform like a single sensor with an extended sonic cone. When a synchronised sensor switches, the target may be in front of the switching sensor as well as in front of one of the other sensors. Typical applications are level control monitoring with more than two switching points or large-scale ramp control tasks.

Alternate sensor operation (multiplexing)
Ultrasonic sensors, which operate alternately, are fully independent from each other and mutual influencing is impossible. The more sensors are operated alternately, the lower the switching frequency. The X1-line of the sensor series RUC…- M30, RU…-Q30 and RU…-M18 can also be used as an enable input for multiplex purposes. If the X1-line is connected to +24 V, the sensor is enabled; if the X1-line is connected to 0 V, the sensor is disabled. Multiplexing via the X1-line has the advantage that for each enable-operation only the response time and not also the time-delay before availability has to be considered.
When using the programming device RU-PDI most sensors can be programmed automatically for multiplex operation by connecting the X1 lines.

Standard target
● Square sound-reflective plate used to determine the rated switching distance sn
● 1 mm thick
● Alignment: vertical to the sonic axis Degree of protection
● Protection of housing against solid bodies and water
● IP65: full protection against dust; protection against of water
● IP67: full protection against dust; protection against submersion in water at a depth of 1 m for 30 minutes at constant temperature
● IP69K: high pressure cleaning according to DIN 40050-9 based on EN 60529