To each their own ultrasonic sensor

SNT Sensortechnik AG: Ultrasonic sensors are suitable for detecting objects with different size and surface finish as well as in a wide variety of distances. The innovative Swiss manufacturer SNT Sensortechnik AG has launched a new family of sensors on the market, which is now being developed for specific applications in a modular system.

Ultrasonic sensors emit a pulsed, high frequency acoustic signal reflected from the target. From the measured time of flight, the distance to the object can be calculated. Depending on the measuring distance, the accuracy is within 1/10 mm to a few mm. In the air, the sound propagation is greatly attenuated, which is why the coverage is limited to a few meters. In water, for instance, the range is much higher. Because of the large sound attenuation in the air the reflected echo signal is extremely small - up to 100'000x smaller than the emitted one. The challenge is therefore on the one hand to send with high sound power and secondly filter out the smallest signals of a large noise level reliably. SNT Sensortechnik AG uses high transmission voltages and in the new series a sophisticated software algorithm from the telecommunications technology..

Depending on the propagation medium the so-called sound transducer must be adjusted accordingly. One speaks of the adaptation to the acoustic impedance Z of the transmission medium. Transducers for air applications should have the minimum possible density and a low modulus of elasticity. This has resulted for industrial ultrasonic sensors for automation technology in transducers, which are equipped with a so-called matching layer between the piezoelectric element and the surroundings. It consists of a resin filled with hollow glass spheres. This material is lightweight yet durable. SNT Sensor-technik AG is developing and producing the sound transducers in-house.

Their advantages over optical, inductive and capacitive sensors play the ultrasonic sensors by the following properties:

• Measuring independent of material, surface, color and size of target
• Work under dust, dirt, fog, bright light
• Detect transparent and bright objects
• Scan sheet-like (and not only point-like)

Thereby ultrasonic sensors can detect different materials such as metals, plastics, wood, liquids, granulates, powders, food, etc. Whether the object is transparent or not, doesn’t matter. So polyvalent are basically only ultrasonic sensors. Therefore they are mainly used when all other methods have failed.

Standard

Even the standard version of the new ultrasonic sensor generation series UPR-A is so versatile that with only 2 types many different applications can be served. The sensor in M18 housing has a maximum range of 1.5m. It can be programmed with one teach input. A specific property is the ability to adjust the size of the detection beam.

Analog output

• e.g. for level measurement
• automatic switch to V or mA output
• programmable characteristics
• programmable sound cone
• standard sensor with axial sound exit
• angled version with radial sound exit

Binary switching output

• e.g. for presence control
• programmable detection window as NO or NC
• programmable sound cone
• standard sensor with axial sound exit
• angled version with radial sound exit
• Retroreflective mode
  
  • for difficult objects to be detected in front of a background

Resistant to chemicals

The UPR-A CP sensors are specifically designed for use in aggressive environments. The high resistance is based on PVDF and PTFE. One possible application is the level measurement of acids and alkalis in containers up to 1.5m depth. The basic sensor is a model UPRA. The media exposed front part is made of PVDF. The outstanding feature of this sensor is the fact that the ultrasonic transducer is completely enclosed with a special PTFE film which transmits the ultrasonic waves. The technical data correspond to those of the UPR-A standard sensors.

ATEX

When working with explosive substances, the plant operator has to carry out a safety analysis according to the ATEX directive and its resulting zone classification. According to the defined zone, the operator must then select an approved sensor for the zone.

Among others, there are the zones 2 (gas) and 22 (dust). These are areas in which an explosive atmosphere does not normally occur or occurs only briefly during normal operation. Especially in connection with dust, there are many such areas in the industry. For these areas, there is now a UPR-A Ex sensor. It is based on the UPR-A series and can be programmed as well.

Stainless steel

Most ultrasonic sensors have a housing made of plastic or nickel plated brass. This is mainly a question of cost. In certain applications and industries the material requirements are however higher. For instance for outdoor applications or harsh cleaning processes or due to special rules for example:

• food industry
• chemical equipment
• pulp industry
• textile Industry
• paint industry
• pharmaceutical Industry
• wastewater treatment
• seawater contact

The new stainless steel sensor UPR A V4A has a housing made of this highest level stainless steel (1.4571). True to the motto: "V2A does not rust - V4A does not rust at all".

The Plan B

The sensor versions described above are evolutions of the standard type. As "B-Variant" UPR-B an even more cost-effective, scaled-down version has now been developed. Thanks to this simplification the sensor is also 30mm shorter, which makes it really a low-cost miniature sensor.

Some typical applications include:

• Min. / Max. level detection of liquids, granules and solids
• Monitoring of liquid levels in filling plants
• Checking for tailbacks on conveyor systems
• Count and detect any object
• Recognizing full or empty pallets and containers

The UPR toolkit: To each his own ultrasonic sensor

• UPR-A: standard
• UPR-A CP: chemically resistant
• UPR-A Ex: ATEX 2/22
• UPR-A V4A: full stainless steel
• UPR-B: short, low cost