Thomas Thurner

A novel capacitance sensor principle applicable for spatially resolving downhole measurements

The paper presents a new approach for the design of capacitive sensors capable of determining the permittivity distribution within a pipe. Due to the robust design and the simple geometry of the sensor, the proposed principle is applicable for downhole measurement systems even when operated at extreme environmental conditions. Results of fill level and water fraction measurements at ambient conditions are presented. For these measurements a prototype sensor was realized and applied to examine a glycerol-water mixture of varying fill level and water fraction within a tube.

Low-Latency Shack–Hartmann Wavefront Sensor Based on an Industrial Smart Camera

Wavefront sensing is important in various optical measurement systems, particularly in the field of adaptive optics (AO). For AO systems, the sampling rate, as well as the latency time, of the wavefront sensors (WFSs) imposes a restriction on the overall achievable temporal resolution. In this paper, we propose a versatile Shack–Hartmann WFS based on an industrial smart camera for high-performance measurements of wavefront deformations, using a low-cost field-programmable gate array as the parallel processing platform. The proposed wavefront reconstruction adds a processing latency of only 740 ns for calculating wavefront characteristics from the pixel stream of the image sensor, providing great potential for demanding AO system designs.

Condition monitoring for reciprocating aircraft engines using fuzzy logic

This paper describes a method for monitoring the condition of reciprocating aircraft engines. In contrast to existing solutions our method is based on information from a single acceleration sensor attached onto the motor block. Model based signal processing using modal analysis and fuzzy logic in a hierarchical estimation scheme enables the possibility to observe engine health level. For each cylinder of the reciprocating system misfire detection and the identification of combustion failures on a per cylinder basis is possible.

Accuracy of Local Conduction Velocity Determination from Non-Fractionated Cardiac Activation Signals

Local velocity and direction of cardiac excitation spread can be estimated from four extra-cellular electric potential waveforms recorded simultaneously by closely-spaced electrodes. In this work, three methods for the determination of these parameters in case of non-fractionated electrograms were compared. Waveforms recorded during in-vitro experiments were analyzed in terms of their noise components. Noise according to the experimental environment was generated and added to noise-free waveforms obtained from computer simulations. For each of the three investigated methods the accuracy of the determined parameters velocity and direction was evaluated for three different noise levels and three types of propagation.

A laser speckle sensor for single-point measurement of strain

Single spot measurement of strain and displacement is very desirable in some applications, especially if the measurement spot can be very small. In this paper we introduce a single point strain measurement principle based on objective speckle correlation using just one CCD array sensor. The method yields one component of the strain in the plane of the surface of the specimen. It is insensitive to strain in the perpendicular direction, and to in-plane displacements of the surface. Measurements on thermal stress in a heated aluminium specimen have been made and are found to be consistent with two other independent strain measurements. The uncertainty of measurement can be as low as 5 microstrain. The dependence of the uncertainty on the diameter of the illuminated spot and on other factors is discussed.

Compensation Based Displacement Measurement Using Objective Laser Speckles

Abstract Objective laser speckles can be observed as intensity pattern from free space propagation of coherent light that is diffracted from a technically rough surface. Utilizing this pattern allows for very localized non-contacting measurement of surface displacement as well as strain, and carries a high potential for miniaturization. Existing objective speckle techniques suffer from decorrelation effects, dramatically decreasing the performance of such measurement techniques. In this paper we present a compensation based displacement measurement scheme, where we keep the measured speckle pattern displacement close to zero by actively following the measuring objects movement in a feedback operation. This converts the image sensor into a zero-detector, what considerably improves the speckle pattern correlation over a significantly extended measurement range.

Shack-Hartmann wavefront sensor based on an industrial smart camera

Wavefront sensing is important in many optical measurement systems and adaptive optics. The speed of the wavefront sensor determines the achievable temporal resolution of dynamic measurements and the bandwidth of adaptive optics systems. In this paper we propose a versatile high-speed Shack-Hartmann wavefront sensor based on an industrial smart camera. The sensor uses a parallel processing scheme for high-speed measurement of wavefront deformations and offers runtime reconfiguration. An FPGA based centroid detection is presented, adding an overall time delay of only 380ns. The wavefront estimation is demonstrated on an external PC using zonal and modal reconstruction.

Runtime-reconfigurable communication concept for real-time measurement and control

In the field of communication between the variant sensor and actuator devices in measurement and instrumentation systems, currently a change of key technologies is underway: The traditional field bus concepts are replaced by state-of-the-art communication systems. Many of these new designs are based on Industrial Ethernet. This paper presents key requirements for an Ethernet-based communication network which is reconfigurable at runtime and provides hard real-time behavior. Based on these requirements an architectural and topological concept is developed and one of the currently leading industrial solutions, EtherCAT, is examined in respect of using it as communication protocol in the proposed system architecture.

Optical 2D Displacement and Strain Sensor for Creep Testing of Material Samples in Transparent Fluids

The designer of mechanical products needs to know the behaviour of the applied materials under different environmental conditions. A standard experiment used to determine these behavioural parameters is the creep test. Certain groups of materials such as polymers exhibit large sensitivities of these parameters with respect to environmental conditions such as temperature and exposure to chemicals. In these cases creep tests need to be performed under conditions that match as closely as possible the service conditions, i.e. conditions under which the material will be used. The physical measurands observed during theses tests are displacement and consequently strain. In general, it is difficult to achieve the long-term stability and accuracy required by creep tests as these experiments usually last for more than thousand hours. The present paper reports on the design and implementation of an optical sensor for 2D displacement and strain measurements in transparent fluids. The proposed sensor meets the accuracy requirements imposed by the creep test procedure. Further, the sensor is insensitive to homogeneous changes in the optical path and thus is well suited for long-term displacement measurements in transparent fluids.

Phase-based Algorithm for 2D Displacement Estimation of Laser Speckle Patterns

Robust, computationally efficient and accurate estimation of 2D speckle pattern displacement is the key signal processing task in most digital speckle photography principles. State-of-the-art techniques are based on the evaluation of correlation functions with high computational complexity when sub-pixel accuracy is needed. Within this paper we describe a new algorithm based on the evaluation of 2D phase data of laser speckle patterns, capable of estimating 2D speckle pattern displacement with reduced computational effort but high resolution when compared to correlation-based processing methods. Using our new algorithm, the resolution and measurement rate of some digital speckle photography principles could be noticeably improved.