Non-Contacting Acoustic Sensors

Sensors for NIVELTRONIC Plus®, the VÖGELE System for Automated Grade and Slope Control.

With NIVELTRONIC Plus®, VÖGELE offer a unique System for Automated Grade and Slope Control creating the basis for efficient paving true to line and level on any base. The high degree of accuracy during paving is achieved through the possibility to combine NIVELTRONIC Plus® with various VÖGELE sensors. The right sensor is available for every paving application, ranging from mechanical sensors to a diverse array of non-contacting sensors. In Part 1 of this series, we present the non-contacting acoustic sensors for the NIVELTRONIC Plus® Automated Grade and Slope Control System.

NIVELTRONIC Plus® is an in-house development of VÖGELE and based on many years of experience in grade and slope control technology. In terms of easy handling, accuracy and reliability, it is the perfect solution to all grade and slope control jobs.

Perfect harmonization between paver and grade and slope control system for maximum pavement quality

The fully integrated system offers the advantage that the machine technology of the SUPER pavers on the one hand and the grade and slope control system on the other are perfectly matched. All cables and connections are integrated into the tractor unit and screed, thus eliminating any confusion of cables and risk of damage.

Wide variety of sensors

VÖGELE offer a wide selection of sensors geared to practice that allow versatile use of the NIVELTRONIC Plus® system. Whether car parks, roundabouts or highways need to be built or rehabilitated, VÖGELE have the right sensor for every job site situation. What’s more, no time is lost when changing sensors, as NIVELTRONIC Plus® automatically recognizes every sensor connected. This allows fast and easy set-up of the system. The different sensors offered by VÖGELE are categorized into three groups: mechanical sensors, non-contacting acoustic or optical sensors, and 3D systems. Part 1 of this series is dedicated to non-contacting acoustic sensors.

Non-contacting Acoustic Sensors

VÖGELE offer 3 different non-contacting acoustic sensors: the Single-Cell Sonic Sensor, the Multi-Cell Sonic Sensor and the Big MultiPlex Ski. The functional principle of all three sensors is identical: an acoustic signal is emitted, reflected and received. The time that elapses between emission and reception of the signal provides information on the distance the signal travelled. As the speed of sound is dependent on temperature, a temperature compensating value is determined by the sensors. This way, grade control of consistent accuracy is ensured even in the case of temperature fluctuations.

No wear of sensors

Based on their identical functional principles, the sensors have common characteristics as far as their advantage over mechanical sensors is concerned. Sonic sensors feature a large measuring and operating range, making them extremely flexible to use. As the sensors operate on a non-contacting basis, they are insusceptible to dirt or wear. Another advantage of their non-contacting operation is that the sensors can remain installed on the paver when moving the machine on the job site. And, in contrast to optical sensors, the acoustic sensors are not influenced by light reflection or light refraction.

Various fields of application

So far the characteristics which these sensors have in common. Of course, there are also differences. An essential difference lies in the number of measurements which are made and analyzed. From this feature result the different fields of application for the Single-Cell Sonic Sensor, the Multi-Cell Sonic Sensor and the Big MultiPlex Ski.

1. Single-Cell Sonic Sensor

The Single-Cell Sonic Sensor has just one sensor cell emitting a sound cone and, therefore, copies a reference in the ratio of 1:1, without calculating an average. This sensor can be used to scan the most varied references and adapts easily to different job site conditions. It, furthermore, stands out through fast and easy installation and operation. On this sensor, the value for temperature compensation is determined by a metal bow fitted at a firm distance to the sensor cell. The sound cone emitted by the sensor cell reaches the metal bow and picks up the distance. If the picked up value deviates from the firm one for the distance, the difference serves as a correction value for the sensor.

Optimal for tight curves

On account of its compact dimensions, the Single-Cell Sonic Sensor is ideally suited for use in confined spaces or on winding roads with small curve radii. It is also recommended in all those cases where precise copying of a reference is desired. Such an example is paving two parallel strips “hot to hot” or “hot to cold”. Furthermore, the Single-Cell Sonic Sensor is the preferred choice on jobs where major changes in layer thickness need to be initiated within a short time, e.g. in the case of speed humps.

2. Multi-Cell Sonic Sensor

Other than the Single-Cell Sonic Sensor with one sensor cell, the Multi-Cell Sonic Sensor is provided with 5 sensor cells emitting 5 sound cones for grade control. Out of these five measurements, however, just 3 are used to calculate an average. The 2 measurements with the greatest deviation from the specified grade are ignored. This automatically prevents unrealistic irregularities in the reference, for instance obstacles like shovels, from being included into grade control.

Sixth sensor cell checks the temperature

As already described, the Single-Cell Sonic Sensor uses a metal bow to compensate temperature fluctuations. With the Multi-Cell Sonic Sensor, this function is fulfilled by an extra sensor cell picking up deviations in sound speed and initiating a correction.

Tensioned wire can also be used as a reference

The VÖGELE Multi-Cell Sonic Sensor features high versatility. By calculating an average from measurements, it can perfectly level out short irregularities in the base. The sensor is suited not only to scanning the ground, but also a tensioned wire or stringline with a minimum thickness of 2.5mm. For such an application, the sensor is positioned at right angles to the direction of motion, i.e. rotated through 90° compared to its “Ground Mode” position. On the screed console, in the menu of NIVELTRONIC Plus®, the screed operator then changes from “Ground Mode” to “Stringline Mode”. After that, an average is no longer calculated and only the measurement of the sound cone with the smallest deviation from the reference used for grade control. In this mode, a reference can be copied on a 1:1 basis, just as with the Single-Cell Sonic Sensor.

3. Big MultiPlex Ski

The Big MultiPlex Ski operates with 3 Multi-Cell Sonic Sensors fitted to a beam. Each of these sensors transmits its measurement (mean value) to the control unit of the Big MultipPlex Ski. The control unit calculates an average of the mean values and passes it on to NIVELTRONIC Plus®, the System for Automated Grade and Slope Control. Obstacles exceeding a defined size are automatically excluded from grade control. This ensures that paving work is always based on correct data.

Variable beam length up to 13m

Thanks to the modular design of the beam, the Big MultiPlex Ski can cover distances ranging from 5 to 13m. The beam itself is made up of several elements. The individual Multi-Cell Sonic Sensors can be shifted on the beam for optimal adjustment in position to job site conditions. The beam length most commonly used in practice is 8m or longer.

Perfect levelling of long irregularities

The Big MultiPlex Ski is particularly suited to paving jobs that call for absolute evenness in the pavement’s longitudinal direction. Thanks to the calculation of an average based on the measurements of several Multi-Cell Sonic Sensors, the system can detect long irregularities in the base which a single Multi-Cell Sonic Sensor would not be capable of recognizing as a fault. Use of the Big MultiPlex Ski is also extremely helpful when it comes to paving perfect transitions to existing surfaces, without a need for manual grade control.

Scanning within or outside the pave width

The Big MultiPlex Ski offers two options for mounting. One of them allows scanning the base within the pave width. To this end, the beam is attached to the screed arm. The special advantage: the freshly paved surface behind the screed becomes part of the reference and is included in grade control. As an alternative, the beam of the Big MultiPlex Ski can be attached to the screed’s end plate if the area outside the machine’s pave width is better suited to scanning.

Selection: The Optimal Sensor for Every Paving Application