Special issue  

This paper describes an optical sensor system based on the technique of laser speckle photometry (LSP) for the application of stress characterization and defect detection in ceramics. The purpose of the research is to develop an in-line inspection solution for the industrial field. The preliminary results show that the LSP technique has the potential to fulfill the task.

This paper covers the design study of a multicomponent transducer (MCT) for wind turbine test benches. The MCT will cover the characteristics of wind turbines in the power range of up to 6 MW. The motivation to develop a MCT such as this is to provide satisfying measurement accuracy of loads and moments for all 6 degrees of freedom in order to reduce the uncertainty in the traceability of the drive train behavior due to the applied loads.

Photoelasticity is considered a useful measurement tool for non-destructive and contactless determination of mechanical stresses or strains in the production of silicon wafers. In this work, a detailed derivation for the anisotropic stress-optic law is presented, and the corresponding stress-optical parameters are measured.

A completely new evaluation method for optical sensors is investigated in this paper. It originates from research that integrates optical sensors into radio-over-fibre networks. The laboratory-based experimental set-up is explained, and the findings are validated by a comparison to the conventional evaluation scheme. Finally, the work provides a detailed mathematical model to understand the implications of this new read-out method for practical applications.

European EMPIR project MicroProbes aims to use large-cale tactile microprobes for contact resonance applications, an established measurement mode of atomic force microscopes (AFMs). Because of the size of these probes, some of the simplifications made for AFM probes are not applicable. This study presents a guide on how to systematically create a model that replicates the dynamic behavior of microprobes. The finished model is then verified by analyzing a series of measurements.

For the determination of the refractive index of the lubricant used in the sheet-bulk metal forming process, a lubricant thin-film thickness standard was developed which represents a continuous measuring range from 6 to 100 μm. To determine the refractive index, the thin-film thickness standard was measured with a coaxial interferometric measurement system in various thickness ranges. The results show changing optical properties with increasing layer thickness.

Detecting faults in bearings is indispensable for the maintenance of many industrial machines or components. The faults are detected by recognizing patterns in vibration data that are measured at the bearing housing. The method can be trained with data of variable revolution speeds, therefore reducing the effort for the acquisition of training data. Moreover, incipient faults can be detected before they cause severe damage to the equipment.

In order to differentiate between a wet and a dry road surface, the water film height should be measured by using an infrared-based sensor system. By means of different wavelengths, it is also possible to distinguish between ice and water. In this article, a sensor system for the determination of the physical state of water on different surfaces using infrared LEDs and one photodiode is presented. This shall serve as a basis for the calculation of the road condition.

Air-coupled ultrasound is a non-contact non-destructive testing method. In many cases air-coupled ultrasound is used in a transmission mode requiring access from both sides of the specimen. Air-coupled ultrasound can be used in a re-emission mode enabling single-sided testing. In this work a sensor head with automatically adjustable ultrasound probes was developed to make one-sided air-coupled ultrasound easier. With this integrated sensor head it is possible to detect defects in thin walls.

The refrigerant R134a is classified as a greenhouse gas and was banned from use (in vehicles) by the European Union in 2017 due to its contribution to global warming. The more expensive alternative refrigerant R1234yf is considered an environmentally less harmful alternative owing to its significantly lower global warming potential. Our newly developed gas detector can detect both refrigerants separately and, thus, help prevent the use of illegal gas mixtures that contain both refrigerants.

The High-Luminosity Large Hadron Collider (HL-LHC) project at CERN will require new superconducting magnets with strict requirements in terms of field quality. A new measurement system based on rotating coils has been developed to characterize them with high accuracy. The system measures the required quantities in a single run, which greatly reduces the necessary time and resources. Thanks to its versatility, it can be adapted to a variety of magnet sizes without major effort.

In this work, a self-actuated microcantilever is used as a flow sensor. Its resonance frequency, resonance amplitude and static deflection are measured. Most conventional flow sensors are often only calibrated for one type of gas and allow an analysis of gas mixtures only with increased effort. The work examines whether the volumetric flow and the mixing ratio of a binary gas mixture are possible simultaneously from these measured variables.

The framework of the single point uncertainty presents a methodology to determine the local measurement uncertainty for a measurement setup. The targets of the investigation were spur (involute) steel gear wheels using a CMM in scanning mode in combination with a rotatory table, as well as a single scan of the complete gear profile without the use of a rotatory table, using the free-form scan CMM functionality. Both methods were examined with respect to their obtained single point uncertainty.

This paper aims to demonstrate the complete workflow of the determination of the local measurement uncertainty and its components (systematic and random measurement error) for a given measurement task. It was shown for an optical measurement setup in combination with an industrial X-ray computed tomography reference measurement system that different necessary colouring methods of polymer gear wheels have a measurable influence on the local distribution of the measurement uncertainty.

A new approach with an acousto-thermal nondestructive testing technique was developed and integrated into a mobile prototype NDT device. It is based on well-known ultrasonic thermography and uses hardware, specimen and local defect resonances for efficient excitation. It was specifically designed for fast and easy-to-interpret application in impact damage detection. Its handheld design allows for mobile usage at impact-injured FRP structures with a testing time of only 1 min.

We present a digital holographic sensor system that is capable of measuring the complete topography of machined components with sub-micrometer precision directly inside a tooling machine. This contribution includes detailed information about the architecture of the wireless interferometric sensor HoloPort. Experimental results on milled parts show the performance of the system and illustrate possible inline applications as well as future perspectives for the sensor.

We present a novel method for measuring dynamic changes in respiration parameters due to breathing based on the coupling of two ultra-high-frequency antennae. Our sensor system shows a high reproducibility and a timing similar to a conventional flow sensor. The presented method is a promising candidate to overcome some of the most important technical burdens of measuring respiratory parameters and might be used as a trigger for patient–ventilator synchronization in infants and neonates.

We describe a mechanical model based on the beam theory for the development of a beam-like sensor switch with switching hysteresis for humidity sensing. The hydrogel swelling provides the mechanical energy to deflect the partly hydrogel-covered bending beam via the bimorph effect. From the model, we calculate the deflection of a beam-like sensor switch with and without a switching hysteresis. A beam-like sensor switch was manufactured, and the switching hysteresis was successfully demonstrated.