Validation of a soft sensor network for condition monitoring in hydraulic systems

With increasing digitization, models are more important than ever. Especially their use as soft sensors during operation offers opportunities in cost saving, easy data acquisition and therefore additional functionality of systems. In soft sensor networks there is redundant data acquisition and consequently the occurrence of inconsistent values from different soft sensors is encouraged. The resolution of these data-induced conflicts allows for the detection of changing components characteristics. Hence soft sensor networks can be used to detect wear in system components. In this paper this approach is validated on a test rig. It is found, that the soft sensor network is capable to determine wear and its extent in eccentric screw pumps and valves via data induced conflicts with relatively simple models

Concept validation of a soft sensor network for wear detection in positive displacement pumps

With increasing digitization, models are not only used during the design phase but throughout the life cycle of systems. Especially the use of models as soft sensors during operation offers opportunities in cost saving, easy data acquisition and therefore additional functionality of systems. Soft sensors are models of components that use easily accessible auxiliary quantities to estimate target quantities that are difficult to measure. Networks of soft sensors are the prerequisite for redundant data acquisition in a system and thus encourage the occurrence of data-induced conflicts, i.e., inconsistent values from different soft sensors, which may result from: (i) the breakdown or defect of a measuring sensor, (ii) model uncertainties of the soft sensors, (iii) change of component characteristics, e.g. due to wear. The resolution of these conflicts either leads to greater confidence in the model-based system quantities or allows the detection of changing components characteristics. Hence soft sensor networks can be used to detect wear in system components. Wear in pumps and valves leads to a change in the flow rate and the inner leakage. Therefore, the detection of wear with soft sensors requires the detection of small changes in the system flow rates. In the full paper an analysis of the influence of small flow rate variations on redundant soft sensor outputs is carried out. For this, small flow rate variations are implemented on a test bench for positive displacement pumps. Furthermore, a systematic analysis of parameter and data uncertainties and their propagation in models for positive displacement pumps is carried out. The resulting flow rates and the measurement uncertainties from the models of the pump and the throttle valve of the test bench are compared and discussed with respect to data induced conflicts and the detection of wear

Resonance Fluorescence Spectrum of a Trapped Ion Undergoing Quantum Jumps

We experimentally investigate the resonance fluorescence spectrum of single 171Yb and 172Yb ions which are laser cooled to the Lamb-Dicke regime in a radiofrequency trap. While the fluorescence scattering of 172Yb is continuous, the 171Yb fluorescence is interrupted by quantum jumps because a nonvanishing rate of spontaneous transitions leads to electron shelving in the metastable hyperfine sublevel 2D3/2(F=2). The average duration of the resulting dark periods can be varied by changing the intensity of a repumping laser field. Optical heterodyne detection is employed to analyze the fluorescence spectrum near the Rayleigh elastic scattering peak. It is found that the stochastic modulation of the fluorescence emission by quantum jumps gives rise to a Lorentzian component in the fluorescence spectrum, and that the linewidth of this component varies according to the average duration of the dark fluorescence periods. The experimental observations are in quantitative agreement with theoretical predictions.Comment: 14 pages including 4 figures, pdf file, fig.1 replace

Fluorescence spectrum of a two-level atom driven by a multiple modulated field

We investigate the fluorescence spectrum of a two-level atom driven by a multiple amplitude-modulated field. The driving held is modeled as a polychromatic field composed of a strong central (resonant) component and a large number of symmetrically detuned sideband fields displaced from the central component by integer multiples of a constant detuning. Spectra obtained here differ qualitatively from those observed for a single pair of modulating fields [B. Blind, P.R. Fontana, and P. Thomann, J. Phys. B 13, 2717 (1980)]. In the case of a small number of the modulating fields, a multipeaked spectrum is obtained with the spectral features located at fixed frequencies that are independent of the number of modulating fields and their Rabi frequencies. As the number of the modulating fields increases, the spectrum ultimately evolves to the well-known Mellow triplet with the sidebands shifted from the central component by an effective Rabi frequency whose magnitude depends on the initial relative phases of the components of the driving held. For equal relative phases, the effective Rabi frequency of the driving field can be reduced to zero resulting in the disappearance of fluorescence spectrum, i.e., the atom can stop interacting with the field. When the central component and the modulating fields are 180 degrees out of phase, the spectrum retains its triplet structure with the sidebands located at frequencies equal to the sum of the Rabi frequencies of the component of the driving field. Moreover, we shaw that the frequency of spontaneous emission can be controlled and switched from one frequency to another when the Rabi frequency or initial phase of the modulating fields are varied

Bayesian estimation of agent-based models

We consider Bayesian inference techniques for agent-based (AB) models, as an alternative to simulated minimum distance (SMD). Three computationally heavy steps are involved: (i) simulating the model, (ii) estimating the likelihood and (iii) sampling from the posterior distribution of the parameters. Computational complexity of AB models implies that efficient techniques have to be used with respect to points (ii) and (iii), possibly involving approximations. We first discuss non-parametric (kernel density) estimation of the likelihood, coupled with Markov chain Monte Carlo sampling schemes. We then turn to parametric approximations of the likelihood, which can be derived by observing the distribution of the simulation outcomes around the statistical equilibria, or by assuming a specific form for the distribution of external deviations in the data. Finally, we introduce Approximate Bayesian Computation techniques for likelihood-free estimation. These allow embedding SMD methods in a Bayesian framework, and are particularly suited when robust estimation is needed. These techniques are first tested in a simple price discovery model with one parameter, and then employed to estimate the behavioural macroeconomic model of De Grauwe (2012), with nine unknown parameters

Hydrospeicher mit Adsorbentien

Hydrospeicher werden in hydro-pneumatischen Federbeinen zur Schwingungsisolation eingesetzt. Ein kompressibles Gas im Hydrospeicher dient als Feder und wird zyklisch komprimiert und expandiert. Wie bei jedem Feder-Masse-System gilt, je niedriger die Federsteifigkeit, desto besser die Isolation bei gegebener Masse. Die Federsteifigkeit sinkt allerdings mit steigendem Bauvolumen des Hydrospeichers. Am Institut für Fluidsystemtechnik entstand die Idee, Hydrospeicher durch das Einbringen hochporöser Adsorbentien wie Aktivkohle, bei gleicher Steifigkeit kleiner bauen zu können. In Abhängigkeit des Drucks lagern sich Gasmoleküle an die Oberfläche der Adsorbentien an und tragen nicht mehr zum Gasdruck bei. Die Steifigkeit der Hydrospeicher sinkt. Allerdings wird bei Adsorption Wärme frei, die insbesondere bei schneller Anregung und damit isentroper Zustandsänderung den Effekt der Steifigkeitsreduktion teilweise wieder aufhebt. Diese Arbeit beantwortet mit Hilfe zweier Modelle und Messungen die Frage, wie groß das Potential zur Bauraumreduktion durch Adsorbentien in hydro-pneumatischen Federbeinen ist