SNR Degradation in Undersampled Phase Measurement Systems

Self Cite

Transimpedance amplifiers (TIA) are widely used for front-end signal conditioning in many optical distance measuring applications in which high accuracy is often required. Small effects due to the real characteristics of the components and the parasitic elements in the circuit board may cause the error to rise to unacceptable levels. In this work we study these effects on the TIA delay time error and deduce analytic expressions, taking into account the trade-off between the uncertainties caused by the delay time instability and by the signal-to-noise ratio. A specific continuous-wave phase-shift case study is shown to illustrate the analysis, and further compared with real measurements. General strategies and conclusions, useful for designers of this kind of system, are extracted too. The study and results show that the delay time thermal stability is a key determinant factor in the measured distance accuracy and, without an adequate design, moderate temperature variations of the TIA can cause extremely high measurement errors.

Section: Resultsmentioning

confidence: 99%

Phase Stability under Thermal Drifts in Photodiode-Conditioning Transimpedance Amplifiers for Distance Metrology

Meca

Martín-Gorostiza

García-Garrido

et al. 2021

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“…As demonstrated in [48], the variance σi2 can be expressed as the inverse of the signal to noise ratio at every anchor (SNRi), and can be modelled as follows σi2=γSNRi=KIR·di4 where the factor γ is proved to be γ=1 [48], di is the Euclidean distance (true value) between bold-italicAbold-italici and T, and KIR is a constant encompassing all parameters of the IR system (including devices, electronics, noise and geometry), as follows:KIR=Pe·As·R·GA·KF·KI/Q·H2η·BWN−1…”

Section: Infrared Estimation Modelmentioning

confidence: 90%

An Indoor Positioning Approach Based on Fusion of Cameras and Infrared Sensors

Martín-Gorostiza

García-Garrido

Pizarro

et al. 2019

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A method for infrared and cameras sensor fusion, applied to indoor positioning in intelligent spaces, is proposed in this work. The fused position is obtained with a maximum likelihood estimator from infrared and camera independent observations. Specific models are proposed for variance propagation from infrared and camera observations (phase shifts and image respectively) to their respective position estimates and to the final fused estimation. Model simulations are compared with real measurements in a setup designed to validate the system. The difference between theoretical prediction and real measurements is between 0.4 cm (fusion) and 2.5 cm (camera), within a 95% confidence margin. The positioning precision is in the cm level (sub-cm level can be achieved at most tested positions) in a 4 × 3 m locating cell with 5 infrared detectors on the ceiling and one single camera, at distances from target up to 5 m and 7 m respectively. Due to the low cost system design and the results observed, the system is expected to be feasible and scalable to large real spaces.

“…For both measuring systems, the precision of the measurement depends significantly on the energy reflected back from the structure and thus on its backscatter properties in the corresponding wavelength band, as the phase measurement accuracy is directly coupled to the signal-to-noise ratio (SNR) of the reflected signal [ 44 ].…”

Section: Theoretical Comparison Of the Sensors For The Contactless Mo...mentioning

confidence: 99%

Contactless Deformation Monitoring of Bridges with Spatio-Temporal Resolution: Profile Scanning and Microwave Interferometry

Schill

Michel

Firus³

2022

Against the background of an aging infrastructure, the condition assessment process of existing bridges is becoming an ever more challenging task for structural engineers. Short-term measurements and structural monitoring are valuable tools that can lead to a more accurate assessment of the remaining service life of structures. In this context, contactless sensors have great potential, as a wide range of applications can already be covered with relatively little effort and without having to interrupt traffic. In particular, profile scanning and microwave interferometry, have become increasingly important in the research field of bridge measurement and monitoring in recent years. In contrast to other contactless displacement sensors, both technologies enable a spatially distributed detection of absolute structural displacements. In addition, their high sampling rate enables the detection of the dynamic structural behaviour. This paper analyses the two sensor types in detail and discusses their advantages and disadvantages for the deformation monitoring of bridges. It focuses on a conceptual comparison between the two technologies and then discusses the main challenges related to their application in real-world structures in operation, highlighting the respective limitations of both sensors. The findings are illustrated with measurement results at a railway bridge in operation.