Search results
1 – 10 of 13Abstract
Details
Keywords
The purpose of this paper is to explore various techniques for detecting gases and particles, with particular application to environmental measurements.
Abstract
Purpose
The purpose of this paper is to explore various techniques for detecting gases and particles, with particular application to environmental measurements.
Design/methodology/approach
The technique and application of infrared absorption sensing of gases is presented, followed by sorbent‐based, catalytic and electrochemical methods. Airborne particle detection techniques are then reported, including filtration, laser scattering and light detection and ranging.
Findings
Various long‐term environmental monitoring programmes measure atmospheric composition and pollution levels. Atmospheric carbon dioxide has increased by 20 per cent since 1958. Hand‐held sensors provide timely warning in fire‐fighting and industrial leakage situations.
Originality/value
Helps the engineer understand the principles of gas and particle detection and the capabilities of portable sensors, and extends general knowledge of environmental programmes.
Details
Keywords
Christopher Hunt, Angela Mensah, Anthony Buxton and Richard Holman
This work sets out to characterise the protective properties of conformal coatings and how they degrade.
Abstract
Purpose
This work sets out to characterise the protective properties of conformal coatings and how they degrade.
Design/methodology/approach
The approach dosed several commercial coatings with two different contaminants, a synthetic generic flux mixture of dibasic acids in both a solvent‐ and water‐based carrier, and sodium chloride. The protective properties were monitored using three complementary techniques: surface insulation resistance measurements, sequential electrochemical reduction analysis, and diffusion measurements.
Findings
The experimental approach was verified and the SIR measurements were shown to be the most valuable. Coatings offered varying levels of resistance to the contaminants, with the silicone coating being the most resistant. The flux variants generally proved more harmful to the coatings, suggesting that flux diffusion through the coating exceeded that of NaCl and hence led to greater electrochemical corrosion. Flux transmission through the coatings was verified by the diffusion measurements.
Research limitations/implications
The project only investigated a limited number of contaminates on simple single sided boards. Future work will investigate coverage effects and a wider range of contaminants.
Practical implications
The work shows that coatings can allow diffusion of contaminates, particularly organics, which can lead to corrosion. The test methodology described here can be used to characterise coating susceptibility.
Originality/value
This work starts to develop for the first time a test methodology to characterise the protective properties of conformal coatings, and shows that flux, and hence other similar organic contaminants, may represent a protection challenge for some coating chemistries.
Details
Keywords
Abstract
Details
Keywords
F.H. Howie and C. Lea
This paper is the second of a series dealing with the blowholing problem on through‐hole plated printed circuit boards. In the previous paper the authors have considered the…
Abstract
This paper is the second of a series dealing with the blowholing problem on through‐hole plated printed circuit boards. In the previous paper the authors have considered the impact of the problem on the UK electronics assembly industry. Here they consider the nature of the gas causing blowholes and voids, its origin and the kinetics of its generation and evolution. When a printed circuit board with plated‐through‐holes is wave soldered, the thermal spike of the molten solder activates the evolution of gas, sometimes in relatively enormous quantities. The gas is seen bubbling from the surface of the molten solder in the joint. Upon freezing, the solder either traps the gas in a void enclosed within the fillet or, if the gas is escaping from the surface as freezing occurs, forms a blowhole.
The long controversy that has waxed furiously around the implementation of the EEC Directives on the inspection of poultry meat and hygiene standards to be observed in poultry…
Abstract
The long controversy that has waxed furiously around the implementation of the EEC Directives on the inspection of poultry meat and hygiene standards to be observed in poultry slaughterhouses, cutting‐up premises, &c, appears to be resolved at last. (The Prayer lodged against the Regulations when they were formally laid before Parliament just before the summer recess, which meant they would have to be debated when the House reassembled, could have resulted in some delay to the early operative dates, but little chance of the main proposals being changed.) The controversy began as soon as the EEC draft directive was published and has continued from the Directive of 1971 with 1975 amendments. There has been long and painstaking study of problems by the Ministry with all interested parties; enforcement was not the least of these. The expansion and growth of the poultry meat industry in the past decade has been tremendous and the constitution of what is virtually a new service, within the framework of general food inspection, was inevitable. None will question the need for efficient inspection or improved and higher standards of hygiene, but the extent of the organization in the first and the enormous cost of structural and other alterations to premises in the second, were seen as formidable tasks, and costly. The execution and enforcement of the new Regulations is assigned to local authorities (District, Metropolitan and London Borough Councils), who are empowered to make charges for inspection, licences, etc., to recoup the full costs of administration. The Government had previously promised that the cost of this new service, which when fully operative, will be significant, would not fall upon the already over‐burdened economies of local authorities. The figure of a penny per bird is given; in those areas with very large poultry processing plants, with annual outputs counted in millions of birds, this levy should adequately cover costs of enforcing the Regulations, but there are many areas with only one of a few small concerns with annual killings of perhaps no more than 200,000 birds—this much we know from perusing annual health reports received at the offices of this Journal—and the returns from charges will certainly be inadequate to cover the cost of extra staff. The Regulations require the appointment of “official veterinary surgeons” and “poultry meat inspectors”, both new to local government.
S. Jones and P. Starkey
Financial and commercial pressures have led to the increasing trend for PCB users to want to reduce or eliminate rework after mass soldering. Whilst the phenomenon of outgassing…
Abstract
Financial and commercial pressures have led to the increasing trend for PCB users to want to reduce or eliminate rework after mass soldering. Whilst the phenomenon of outgassing is recognised, it is not generally well understood by either the manufacturers or users of PCBs. It is the intention of this paper to clarify and focus attention upon some apects of the problem from the manufacturing side of the industry.