An evaluation and comparison of PLC programming techniques : innovation report

Few significant changes in Programmable Logic Controller (PLC) software design techniques have taken place since PLC's were first introduced in the 1960's. Programs written in the traditional language used in PLC's, ladder logic, are generally thought to be difficult to maintain and modify, and thus ill suited to the support of modem flexible manufacturing processes. This work demonstrates that the choice of PLC software structure used in a project has an impact on process flexibility with an appropriate choice providing significant cost savings in development time. An overview of work on formalised programming tools conducted in academia is provided together with a report on the PLC software structures used in industry. The factors influencing the choice of PLC and software structure are identified. Familiarity was found to be a major factor influencing selection. A method for comparing code structures, which allows the results to be expressed as a time saving (and consequently a cost) has been created. Implementation of this approach was used to show that the formalised programming tool under test provides a 33% increase in "right first time" rate together with an 80% time saving over traditional contact based ladder logic. Among experienced practitioners, performance with step-based ladder logic was found to be a close match to the formalised tool, demonstrating that the commonly perceived limitations are the result of the structure in which the language is used rather than a function of the programming tool itself. Further investigation of participant preferences among skilled PLC users showed a mismatch between their performance with a tool and their preference, with at least 25% selecting a tool based on their prior knowledge rather than performance. This highlights the need for the use of objective measures when conducting evaluations between products and technologies. With the information provided in this work, automation end users are provided with a mechanism for ensuring the selection of automation tools best suited to their business needs, whilst at the same time providing automation vendors with the ability to best demonstrate the strengths of the products

Projective prime ideals and localisation in pi-rings

The results here generalise [2, Proposition 4.3] and [9, Theorem 5.11]. We shall prove the following. THEOREM A. Let R be a Noetherian PI-ring. Let P be a non-idempotent prime ideal of R such that PR is projective. Then P is left localisable and RP is a prime principal left and right ideal ring. We also have the following theorem. THEOREM B. Let R be a Noetherian PI-ring. Let M be a non-idempotent maximal ideal of R such that MR is projective. Then M has the left AR-property and M contains a right regular element of R

How successful are International Monetary Fund loan programs?

Abstract. This paper evaluates the effectiveness of International Monetary Fund (IMF) loan programs from 2000 to 2010 by looking at macroeconomic indicators such as the unemployment rate, inflation, real GDP, government debt as a percentage of GDP, and export value. Data is used from the year before the implementation of the IMF loan program to three years after the loan policy was implemented. We chose three years into the future because it gives time for the macroeconomic factors within a country to fully materialize while weeding out much “white noise” (shocks that have nothing to do with the program itself).  Our analysis shows that IMF loan programs between 2000 and 2010 were generally unsuccessful in improving macroeconomic growth and stability in countries that sought loans. An accompanying workbook contains the data.Keywords. IMF; Lending.JEL. F30; F33; F34

Criteria for a ring to have a left Noetherian left quotient ring

Two criteria are given for a ring to have a left Noetherian left quotient ring (to find a criterion was an open problem since 70's). It is proved that each such ring has only finitely many maximal left denominator sets

Understanding the complex needs of automotive training at final assembly lines

Automobile final assembly operators must be highly skilled to succeed in a low automation environment where multiple variants must be assembled in quick succession. This paper presents formal user studies conducted at OPEL and VOLVO Group to identify assembly training needs and a subset of requirements; and to explore potential features of a hypothetical game-based virtual training system. Stakeholder analysis, timeline analysis, link analysis, Hierarchical Task Analysis and thematic content analysis were used to analyse the results of interviews with various stakeholders (17 and 28 participants at OPEL and VOLVO, respectively). The results show that there is a strong case for the implementation of virtual training for assembly tasks. However, it was also revealed that stakeholders would prefer to use a virtual training to complement, rather than replace, training on pre-series vehicles

Contaminant issues in production and application of biochar

For widespread use of biochar in agriculture and horticulture, it must be ensured that application will neither adversely affect soil and plants, nor exceed legislated contaminant concentrations. The most relevant groups of contaminants in biochar are potentially toxic elements (PTEs), polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOC). In this thesis, the concentrations of these groups of contaminants were analysed in 90 different biochars produced by slow pyrolysis. Subsequently, the concentrations were compared to legislation/guideline threshold values and linked to production conditions. The risk these contaminants pose to plant growth was also assessed, to give recommendations on production of safe biochar. PTEs can neither be formed nor destroyed, which means their presence in biochar is predominantly determined by feedstock type. However, significant levels of Cr, Fe and Ni were introduced into biochar from the furnace steel, whilst PTEs with low boiling points, such as As, Cd and Zn, partially evaporated during pyrolysis. PTEs were not responsible for phytotoxic effects observed for PTE-rich biochars despite biochar’s exceedance of available and total PTE threshold values for soil and soil amendments. Although initial tests were promising, the risk that PTE-rich biochars as amendment for soil and growing media pose, needs further investigation. The PAH concentration in biochar was markedly reduced by increasing carrier gas flow rate, and the type of feedstock also influenced the PAH content. However, there was no clear dependence of pyrolysis temperature on PAH concentrations, which was attributed to PAHs being increasingly formed and evaporated at higher pyrolysis temperatures. Ultimately, condensation of pyrolysis vapours and deposition on biochar was identified as the main risk for biochar contamination with PAHs, as this resulted in elevated concentrations of high-risk, higher molecular weight PAHs. Weaknesses in the pyrolysis unit design, such as cold zones, resulted in elevated concentrations of VOCs, as well as PAHs, in biochar. Comparing concentrations and phytotoxic potential of both compound groups, it was concluded that observed toxic effects were much more likely caused by VOCs in biochars containing both contaminants. Overall, formation of VOCs and PAHs cannot be prevented, but their presence in biochar resulting from retention and deposition can be minimised

An evaluation and comparison of PLC programming techniques : innovation report

Few significant changes in Programmable Logic Controller (PLC) software design techniques have taken place since PLC's were first introduced in the 1960's. Programs written in the traditional language used in PLC's, ladder logic, are generally thought to be difficult to maintain and modify, and thus ill suited to the support of modem flexible manufacturing processes. This work demonstrates that the choice of PLC software structure used in a project has an impact on process flexibility with an appropriate choice providing significant cost savings in development time. An overview of work on formalised programming tools conducted in academia is provided together with a report on the PLC software structures used in industry. The factors influencing the choice of PLC and software structure are identified. Familiarity was found to be a major factor influencing selection. A method for comparing code structures, which allows the results to be expressed as a time saving (and consequently a cost) has been created. Implementation of this approach was used to show that the formalised programming tool under test provides a 33% increase in "right first time" rate together with an 80% time saving over traditional contact based ladder logic. Among experienced practitioners, performance with step-based ladder logic was found to be a close match to the formalised tool, demonstrating that the commonly perceived limitations are the result of the structure in which the language is used rather than a function of the programming tool itself. Further investigation of participant preferences among skilled PLC users showed a mismatch between their performance with a tool and their preference, with at least 25% selecting a tool based on their prior knowledge rather than performance. This highlights the need for the use of objective measures when conducting evaluations between products and technologies. With the information provided in this work, automation end users are provided with a mechanism for ensuring the selection of automation tools best suited to their business needs, whilst at the same time providing automation vendors with the ability to best demonstrate the strengths of the products.EThOS - Electronic Theses Online ServiceGBUnited Kingdo