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Przekształtnik SiC DC-DC z transformatorem macierzowym do pokładowych ładowarek baterii akumulatorów taboru 3kV DC
- Marek Adamowicz
- Jędrzej Pietryka
- Zbigniew Krzemiński
2023 Pełny tekst Przegląd Elektrotechniczny
Baterie akumulatorów pojazdów trakcyjnych zapewniają zasilanie krytycznych systemów, takich jak sterowanie i oświetlenie. Zgodnie z wymaganiami przemysłu kolejowego, pokładowa ładowarka baterii akumulatorów powinna być urządzeniem kompaktowym, wysokosprawnym, a jednocześnie wysoce niezawodnym. W referacie, do pokładowego ładowania akumulatorów pociągu zaproponowano kompaktowy przekształtnik SiC DC-DC z transformatorem macierzowym 16:1, zintegrowany z główną przetwornicą pomocniczą pociągu o konstrukcji dachowej. Cały system przetwornicy głównej ze zintegrowaną ładowarką zapewnia przetwarzanie energii z poziomu 3kV DC do poziomu 24V przy zachowaniu wysokiej sprawności.
Przestrzenie publiczne. Ciągłość i zmiana
- Małgorzata Dymnicka
2023
Gdańskie przestrzenie publiczne mają wyjątkową historię, która pozwala widzieć miasto jako kompletne, zwarte i czytelne. W różnych okresach rozwoju stanowiły one element miejskiej tkanki oraz odpowiedź na potrzeby i aspiracje różnych grup oraz społeczności. Miarą atrakcyjności przestrzeni publicznych nie jest już tylko aspekt estetyczny, lecz czyste powietrze, odporność na różne kataklizmy, dostępność do akwenów i obszarów zielonych. Zwrot w myśleniu o przestrzeni publicznej wynika z dostrzeżenia jej roli w kształtowaniu postaw prośrodowiskowych wśród mieszkańców i użytkowników miasta. Gdańszczanie coraz częściej dają sobie prawo do współdecydowania o wielu sprawach publicznych. Można o nich powiedzieć, że stają się aktorami, którzy (współ)tworzą przestrzenie publiczne.
Psychological and physical components in forming preferences on urban greenery management – The case of trees
- Daria Paniotova-maczka
- Piotr Jabkowski
- Piotr Matczak
- Patrycja Przewoźna
- Krzysztof Mączka
- Marcin Mielewczyk
- Adam Inglot
2023 ENVIRONMENTAL SCIENCE & POLICY
Public opinion is increasingly important in managing urban greenery. In this regard, this study demonstrates the importance of sociological (environmental worldviews), psychological (place attachment, perceived benefits of trees), and physical factors (type of building people live in, and urban greenery) in forming residents’ opinions on whether the municipality or landowners should decide about tree removal on private land. Logistic regression models were applied to analyze data collected through a survey (N = 199) and satellite image-derived Normalized Difference Vegetation Index carried out in two Polish cities to predict the likelihood of a respondent indicating whether landowners or the municipality should decide about tree removal on private land. The results revealed that, of two worldviews, Anthropocentrism and Environmentalism, the former is connected with the opinion that the landowner should decide about tree removal. Moreover, a stronger sense of place attachment strengthens this opinion. At the same time, greater recognition of cultural ecosystem services provided by trees and living in multi-family houses is related to the opinion that the municipality should decide about tree removal. The results also demonstrated that, when managing urban greenery, it is vital to consider not only the quality of greenery but also less obvious metrics that can affect tree management. Based on these findings we conclude that the participation of residents in tree management decisions requires careful consideration of social factors affecting their preferences.
Psychometric properties of the Bern illegitimate tasks scale using classical test and item response theories
- Beata Basińska
- Anna Maria Daderman
2023 Pełny tekst Scientific Reports
Combining a classical test theory and an item response theory (IRT), this study aimed to investigate the psychometric properties of the Bern Illegitimate Tasks Scale (BITS) by measuring two conceptually separate dimensions capturing unnecessary tasks (perceived by employees as pointless) and unreasonable tasks (perceived as unfairly or inappropriately assigned). Data collected among Polish employees in two samples (N= 965 and N= 803) were analysed. Results from the classical test theory (parallel analysis, exploratory and confrmatory factor analyses) indicated two correlated factors with four items each, confrming the theory of illegitimate tasks. This study is the frst to report item and scale functioning using IRT analysis of each of the two dimensions of BITS. All items on each dimension had acceptable discrimination and difculty parameters. Moreover, items had measurement invariance between men and women. All levels of unnecessary and unreasonable tasks were reliably captured by BITS items. Convergent and discriminant validities of both dimensions of BITS were confrmed in relation to work overload, work performance and occupational wellbeing. We conclude that BITS, in the case of the Polish version, is psychometrically suitable to use with the working population.
PSYCHOMETRIC PROPERTIES OF THE POLISH VERSION OF THE GENERALIZED ANXIETY DISORDER 7-ITEM SCALE (GAD-7) IN A NON-CLINICAL SAMPLE OF EMPLOYEES DURING PANDEMIC CRISIS
- Beata Basińska
- Zuzanna Kwissa-Gajewska
2023 Pełny tekst International Journal of Occupational Medicine and Environmental Health
Objectives: The COVID-19 outbreak is an example of a crisis that triggered an increase in generalized anxiety disorder. The study aims to validate the Polish version of the Generalized Anxiety Disorder 7-item scale (GAD-7) by Spitzer et al. among a non-clinical sample of employees and examine the invariance depending on the gender and age of working adults. Material and Methods: For assessing factor structure of the Polish version of the GAD-7, the data were collected from a sample of 821 adults employed in 4 economic sectors (health care, education, IT, public administration) during the initial phase of the COVID-19 pandemic in Poland (April 10–May 24, 2020). Due to differences in the severity of GAD symptoms across gender and age groups, the measurement invariance in these groups was tested. Results: The results of a series of confirmatory factor analyses confirmed the unidimensionality of the GAD-7. The values of the composite reliability index and Cronbach’s α showed that it is a reliable tool. The GAD levels demonstrated strong relationships with professional burnout, psychological distress, and psychological complaints. These relationships were stronger than the relationships between these factors and job satisfaction. Construct, metric and scalar invariance across gender and age groups were documented. Women experienced more severe symptoms of generalized anxiety disorder than men. Generalized anxiety disorder affected 28% of respondents. Conclusions: This study contributes evidence of the validation of the GAD among employees and also confirms the invariance depending on gender and age. The Polish version of the GAD-7 has good psychometric properties in a group of professionals and can be recommended for research and to be used in an occupational medicine practice, especially during crisis periods associated with the risk of developing a generalized anxiety disorder.
PV installations and the safety of residential buildings
- Leszek Litzbarski
- Konrad Seklecki
- Marek Adamowicz
- Jacek Grochowski
2023 Pełny tekst Inżynieria Bezpieczeństwa Obiektów Antropogenicznych
The dynamic development of the photovoltaic industry entails threats that have a direct impact on the safety of residential buildings. Appropriate design of a PV installation can be a challenge due to the multifaceted nature of this issue. The designer should take into account issues related to the selection of electrical parameters of the installation, adapting lightning and surge protection in accordance with applicable standards, ensure the optimization of the system in terms of efficiency and fire safety and calculate the mechanical stress on the rooftop. Unfortunately, most PV installations in Poland are built without any engineering project, which is allowed by the current law. In this article, we describe the results of simulations of real mechanical loads inflicted from the installation of PV panels on flat roofs for various regions of Poland. Wealso present the results of the simulation of the thermal impact of hot-spots on the roof surface, which can be a potential source of fire. In addition, we propose changes to the regulations that may increase the safety of PV installations mounted on the roofs of residential buildings
Pyrolysis and Torrefaction—Thermal Treatment of Creosote-Impregnated Railroad Ties as a Method of Utilization
- Paweł Kazimierski
- Paulina Kosmela
- Piotr Piersa
- Szymon Szufa
2023 Pełny tekst Materials
A fundamental issue of waste management and the rail transport industry is the problem of utilizing used railroad ties. Wooden railroad ties are treated with a preservative, usually creosote. Due to their high toxicity, railroad ties are considered hazardous waste and must be utilized under various directives. It is proposed to utilize the troublesome waste by using the pyrolysis and torrefaction process. The research proves that the thermal method is effective for disposing of this type of waste. Torrefaction up to 250 °C gives high efficiency of impregnation removal, while pyrolysis up to 400 °C completely neutralizes waste. A series of experiments were conducted for various final pyrolysis temperatures to determine a minimum temperature for which the obtained solid products are free from creosote. Extraction with the use of the Soxhlet technique was performed for the raw materials and the obtained solid products—chars. The oil content for liquid fraction was also examined for each sample. As a result of the thermal treatment of the waste, fuel with combustion parameters better than wood was obtained. For a high final temperature of the process, the calorific value of char is close to that of hard coal.
Quality 5.0: A Paradigm Shift Towards Proactive Quality Control in Industry 5.0
- Jan Frick
- Piotr Grudowski
2023 Pełny tekst Asia-Pacific Journal of Business Administration
Industry 5.0, the latest wave of industrial revolution, is redefining the traditional manufacturing and production landscapes by leveraging advanced technologies, promoting sustainability, and fostering a human-centric approach. An inevitable consequence of this progression is Quality 5.0, the next phase of quality control and assurance. Quality 5.0 aims to transcend the limitations of conventional quality control techniques, which are typically reactive, by adopting a proactive stance towards defect prevention and process optimization. This paper elucidates the concepts of Quality 5.0, discussing its principles, benefits, and potential challenges in the context of Industry 5.0.
Quality Evaluation of Speech Transmission via Two-way BPL-PLC Voice Communication System in an Underground Mine
- Przemysław Falkowski-Gilski
- Grzegorz Debita
2023 Pełny tekst Archives of Acoustics
In order to design a stable and reliable voice communication system, it is essential to know how many resources are necessary for conveying quality content. These parameters may include objective quality of service (QoS) metrics, such as: available bandwidth, bit error rate (BER), delay, latency as well as subjective quality of experience (QoE) related to user expectations. QoE is expressed as clarity of speech and the ability to interpret voice commands with adequate mean opinion score (MOS) grades. This paper describes a quality evaluation study of a two-way speech transmission system via bandwidth over power line – power line communication (BPL-PLC) technology in an operating underground mine. We investigate how different features of the available wired medium can affect end-user quality. The results of the described study include: two types of coupling (capacitive and inductive), two transmission modes (mode 1 and 11), and four language sets of speech samples (American English, British English, German, and Polish) encoded at three different bit rates (8, 16, and 24 kbps). Our findings can aid both researchers working on low-bit rate coding and compression, signal processing and speech perception, as well as professionals active in the mining and oil industry.
Quantumness in Diagnostics of Marine Internal Combustion Engines and Other Ship Power Plant Machines
- Jacek Rudnicki
- Jerzy Girtler
2023 Pełny tekst Polish Maritime Research
The article provides proof that the diagnostics of marine internal combustion engines and other ship power plant machines should take into account the randomness and unpredictability of certain events, such as wear, damage, the variations of mechanical and thermal loads, etc., which take place during machine operation. In the article, the energy E, like the other forms (methods) that it can be converted into (heat and work), is considered the random variable; at time t, this variable has the mean value, which is the observed value of the some statistic with an asymptotically normal distribution, irrespective of the functional form of the random variable. A proof is given that shows that the expected value estimated in the above way, considering the time t of the performance of task Z by a marine internal combustion engine or other ship power plant machine, can be used to determine the machine’s possible action (DM). When compared to the required action (DW) needed for task Z to be performed, this possible action makes it possible to formulate an operating diagnosis concerning whether the engine or machine of concern is able to perform task Z. It is assumed that an energy device of this type is able to perform a given task when the inequality DM > DW holds. Otherwise, when DM < DW, the device cannot perform the task for which it was adopted in the design and manufacturing phase, which means that it is in the incapability state, although it still can be started and convert energy into the form of heat or work.
Quenching of bright and dark excitons via deep states in the presence of SRH recombination in 2D monolayer materials
- Jędrzej Szmytkowski
2023 Pełny tekst JOURNAL OF PHYSICS-CONDENSED MATTER
Two-dimensional (2D) monolayer materials are interesting systems due to an existence of optically non-active dark excitonic states. In this work, we formulate a theoretical model of an excitonic Auger process which can occur together with the trap-assisted recombination in such 2D structures. The interactions of intravalley excitons (bright and spin-dark ones) and intervalley excitons (momentum-dark ones) with deep states located in the energy midgap have been taken into account. The explanation of this process is important for the understanding of excitonic and photoelectrical processes which can coexist in 2D materials, like transition metal dichalcogenides and perovskites.
Quiet Quitting and its Link With Knowledge Risks in Organizations – Theoretical Insights
- Martyna Gonsiorowska
- Małgorzata Zięba
2023 Pełny tekst
Purpose: Quiet quitting has become a widely publicized concept, driven by social media in the United States and other countries in 2022. It is a term used to describe the phenomenon by which employees do the least amount of their work, just enough to meet the requirements of one’s job description (Mahand and Caldwell, 2023). The trend is spreading quickly among young workers. It can potentially harm individuals, job performance, innovativeness, and whole businesses. Moreover, this phenomenon can also pose several knowledge risks. This conceptual paper aims to identify and analyse human knowledge risks resulting from quiet quitting. Design/methodology/approach: This present study makes an update on the literature linking knowledge risks arising and quiet quitting. Originality/value: To the best knowledge of the authors, there are no publications that describe the knowledge risks arising from quiet quitting. This paper offers new insights for researchers dealing with the topic of knowledge risks in the context of human behaviours. Practical implications: The paper provides insight for each practitioner, as the issue addressed concerns the majority of incumbent employees. Especially, employers and managers should become aware of the consequences related to knowledge risks arising from quiet quitting.
RAGE as a Novel Biomarker for Prostate Cancer: A Systematic Review and Meta-Analysis
- Catherine C. Applegate
- Michael B. Nelappana
- Elaine A. Nielsen
- Leszek Kalinowski
- Iwona T. Dobrucki
- Lawrence W. Dobrucki
2023 Pełny tekst Cancers
The receptor for advanced glycation end-products (RAGE) has been implicated in driving prostate cancer (PCa) growth, aggression, and metastasis through the fueling of chronic inflammation in the tumor microenvironment. This systematic review and meta-analysis summarizes and analyzes the current clinical and preclinical data to provide insight into the relationships among RAGE levels and PCa, cancer grade, and molecular effects. A multi-database search was used to identify original clinical and preclinical research articles examining RAGE expression in PCa. After screening and review, nine clinical and six preclinical articles were included. The associations of RAGE differentiating benign prostate hyperplasia (BPH) or normal prostate from PCa and between tumor grades were estimated using odds ratios (ORs) and associated 95% confidence intervals (CI). Pooled estimates were calculated using random-effect models due to study heterogeneity. The clinical meta-analysis found that RAGE expression was highly likely to be increased in PCa when compared to BPH or normal prostate (OR: 11.3; 95% CI: 4.4–29.1) and that RAGE was overexpressed in high-grade PCa when compared to low-grade PCa (OR: 2.5; 95% CI: 1.8–3.4). In addition, meta-analysis estimates of preclinical studies performed by albatross plot generation found robustly positive associations among RAGE expression/activation and PCa growth and metastatic potential. This review demonstrates that RAGE expression is strongly tied to PCa progression and can serve as an effective diagnostic target to differentiate between healthy prostate, low-grade PCa, and high-grade PCa, with potential theragnostic applications.
Rainwater chemistry composition in Bellsund: Sources of elements and deposition discrepancies in the coastal area (SW Spitsbergen, Svalbard)
- Sara Lehmann-konera
- Ruman Marek
- Marcin Frankowski
- Łukasz Małarzewski
- Krzysztof Raczyński
- Filip Pawlak
- Kozioł Krystyna
- Żaneta Polkowska
2023 CHEMOSPHERE
Discrepancies in rainfall chemistry in Bellsund were found to be influenced by the orographic barrier and related to the variability in the inflow of air masses as well as to the distance of sampling sites from the sea and thus the extent of sea spray impact. This study covers measurements of rainfall (P) and air temperature (T), physicochemical parameters (pH, specific electrolytic conductivity (SEC), major ions (Cl , NO3 , SO4 2 ) and elements (Na, Ca, Mg, K), as well as trace elements (i.a. As, Cd, Cr, Fe, Co, Pb, Ni, Zn) and dissolved organic carbon (DOC) in 22 rainfall samples collected in August on the Calypsostranda marine terrace and in the forefield of a landterminating glacier (NW Wedel Jarlsberg Land). The comparison of chemical parameters in the samples revealed major discrepancies, including statistically significant higher rainwater pH and SEC, and the levels of Ag, As, Bi, Ca, Co, Fe, Li, Mn, Mo, Ni, Pb, Sb, and V, deposited near the seashore (Calypsostranda) than in the glacier forefield. Cluster analysis (CA) showed that elements deposited in lower concentrations at the glacier forefield site came from predominately anthropogenic sources. Conversely, CA results of metals and metalloids deposited on the Calypsostranda marine terrace indicate both natural and anthropogenic sources. A correlation matrix and principal component analysis (PCA) permitted identifying two primary factors affecting rainfall chemistry at each of the study sites. In Calypsostranda, these were the inflow of relatively unpolluted cold air (F1 = 35.1%) and sea spray (F2 = 27.6%), while in the glacier forefield the factors were an orographic barrier (F1 = 37.3%) and the inflow of polluted warm air (F2 = 25.2%).
Rapid and Reliable Re-Design of Miniaturized Microwave Passives by Means of Concurrent Parameter Scaling and Intermittent Local Tuning
- Sławomir Kozieł
- Anna Pietrenko-Dąbrowska
2023 Pełny tekst Scientific Reports
Re-design of microwave passive components for the assumed operating frequencies or substrate parameters is an important yet a tedious process. It requires simultaneous tuning of relevant circuit variables, often over broad ranges thereof, to ensure satisfactory performance of the system. If the operating conditions at the available design are distant from the intended ones, local optimization is typically insufficient, whereas global search entails excessive computational expenses. The problem is aggravated for miniaturized components, typically featuring large numbers of geometry parameters. Furthermore, owing to their tightly-arranged layouts, compact structures exhibit considerable cross-coupling effects. In order to reliably evaluate electrical characteristics under such conditions full-wave electromagnetic (EM) analysis is mandatory. Needless to say, EM-driven design over broad ranges of operating frequencies is an arduous and costly endeavor. In this paper, we introduce a novel procedure for rapid and reliable re-design of microwave passives. Our methodology involves concurrent scaling of geometry parameters interleaved with local (gradient-based) tuning. The scaling stage allows for low-cost relocation of the operating frequencies of the circuit, whereas the optimization stage ensures continuous (iteration-wise) alignment of the performance figures with their target values. The presented framework is validated using several miniaturized microstrip couplers, re-designed over extended ranges of the center frequencies. For all considered structures, satisfactory designs are successfully identified despite the initial designs being distant from the targets, whereas local tuning turns out to be demonstrably inferior. Apart from its efficacy, one of the most important advantages of the proposed framework is its simplicity, and the lack of problem-dependent control parameters.
Rapid Antenna Optimization with Restricted Sensitivity Updates by Automated Dominant Direction Identification
- Anna Pietrenko-Dąbrowska
- Sławomir Kozieł
2023 KNOWLEDGE-BASED SYSTEMS
Meticulous tuning of geometry parameters turns pivotal in improving performance of antenna systems. It is more and more often realized using formal optimization methods, which is demonstrably the most efficient way of handling multiple design variables, objectives, and constraints. Although in some cases a need for launching global search arises, a typical design scenario only requires local optimization, especially when a decent initial design can be rendered using engineering experience or parametric studies. At the same time, antenna optimization is typically conducted using full-wave electromagnetic (EM) simulations, which entails considerable computational expenses. In this paper, we introduce a novel procedure for expedited antenna tuning. Its fundamental mechanism is to restrict the antenna response sensitivity updates to the selected dominant directions within the parameter space, determined based on the problem-specific knowledge, in particular, the estimated changes of antenna characteristics when moving across one-dimensional affine subspaces spanned by these directions. Thus, the said dominant directions affect the most the responses of the antenna structure under design as assessed using the introduced metrics. The decision making process concerning the number of directions to be used relies on quantification of the aggregated system response variability metrics. The proposed approach is demonstrated by means of several antenna structures and benchmarked against conventional trust-region algorithm, but also its accelerated versions. The results indicate considerable (up to over 60%) speedup over the reference procedure without noticeable quality degradation.
Rapid Design of 3D Reflectarray Antennas by Inverse Surrogate Modeling and Regularization
- Sławomir Kozieł
- Mehmet Belen
- Alper Caliskan
- Peyman Mahouti
2023 Pełny tekst IEEE Access
Reflectarrays (RAs) exhibit important advantages over conventional antenna arrays, especially in terms of realizing pencil-beam patterns without the employment of the feeding networks. Unfortunately, microstrip RA implementations feature narrow bandwidths, and are severely affected by losses. A considerably improved performance can be achieved for RAs involving grounded dielectric layers, which are also easy to manufacture using 3D printing technology. Regardless of the implementation details, a practical bottleneck of RA design is the necessity of independent adjustment of a large number of unit cells, which has to be carried out using full-wave electromagnetic (EM) simulation models to ensure reliability. The associated computational costs are extraordinary. A practical workaround is the incorporation of surrogate modeling methods; however, a construction of accurate metamodel requires a large number of training data samples. This letter introduces an alternative RA design approach, where the unit cells are adjusted using an inverse surrogate model established with a small number of anchor points, pre-optimized for the reference reflection phases. To ensure solution uniqueness, the anchor point optimization involves regularization, here, based on the minimum-volume condition for the unit cell. The presented approach reduces the computational cost of RA design to a few dozens of EM analyses of the cell. Several demonstration examples are provided, along with an experimental validation of the selected RA realization.
Rapid multi-criterial design of microwave components with robustness analysis by means of knowledge-based surrogates
- Sławomir Kozieł
- Anna Pietrenko-Dąbrowska
2023 Pełny tekst Scientific Reports
Manufacturing tolerances and uncertainties concerning material parameters, e.g., operating conditions or substrate permittivity are detrimental to characteristics of microwave components. The knowledge of relations between acceptable parameter deviations (not leading to violation of design specifications) and the nominal performance (not considering uncertainties), and is therefore indispensable. This paper proposes a multi-objective optimization technique of microwave components with tolerance analysis. The goal is to identify a set of trade-off designs: nominal performance versus robustness (quantified by the maximum input tolerance values that allow for achieving 100-percent fabrication yield). Our approach exploits knowledge-driven regression predictors rendered using characteristic points (features) of the component’s response for a rapid evaluation of statistical performance figures, along with trust-region algorithm to enable low execution cost as well as convergence. The proposed methodology is verified with the use of three microstrip circuits, a broadband filter, and two branch-line couplers (a single- and a dual-band one). It is demonstrated that a Pareto set w.r.t. nominal performance and robustness objectives can be produced using only 40 to 60 EM simulations of the respective structure (per design). Reliability of the proposed algorithm is corroborated with the use of EM-based Monte Carlo simulation.
Rating by detection: an artifact detection protocol for rating EEG quality with average event duration
- Daniel Węsierski
- Mehrdad Rahimzadeh Rufuie
- Olga Milczarek
- Wojciech Ziembla
- Paweł Ogniewski
- Anna Kołodziejak
- Paweł Niedbalski
2023 Pełny tekst Journal of Neural Engineering
Quantitative evaluation protocols are critical for the development of algorithms that remove artifacts from real EEG optimally. However, visually inspecting the real EEG to select the top-performing artifact removal pipeline is infeasible while hand-crafted EEG data allow assessing artifact removal configurations only in a simulated environment. This study proposes a novel, principled approach for quantitatively evaluating algorithmically corrected EEG without access to ground truth in real-world conditions. Our offline evaluation protocol uses a detector to score the presence of artifacts. It computes their average duration, which measures the recovered EEG's deviation from the modeled background activity with a single score. As we expect the detector to make generalization errors, we employ a generic and configurable Wiener-based artifact removal method to validate the reliability of our detection protocol. Quantitative experiments extensively compare many Wiener filters and show their consistent rankings agree with their theoretical assumptions and expectations. The rating-by-detection protocol with the average event duration (AED) measure should be of value for EEG practitioners and developers. After removing artifacts from real EEG, the protocol experimentally shows that reliable comparisons between many artifact filtering configurations are possible despite the missing ground-truth neural signals.
RCDs Tripping in the Range from DC to AC 50 kHz for Slowly Rising Residual Current
- Hanan Tariq
- Stanisław Czapp
- Vitaly Levashenko
2023
The wide use of power electronic converters means that in many low-voltage systems earth fault currents containing components from DC to AC of various frequencies have to be taken into account. Due to the tendency to increase the modulation frequency in converters, components of higher frequencies may be in the order of several tens of kilohertz. Therefore, it is very important to verify the behavior of devices for protection against electric shock in the presence of earth currents with frequencies other than the nominal frequency of the network, as well as for a DC component. The paper presents the results of tests of residual current devices (RCDs), with slowly rising earth/residual current at selected frequencies within the range 1 Hz – 50 kHz, and at pure DC. Tests have shown that RCDs may not respond to certain frequencies and pure DC, which carries a risk of electric shock.