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Dickon Ross’s editor’s letter in the February issue of E&T poses several questions about the apparently utopian scene portrayed on the front cover. The scene appears to be set in the early 1950s, in which case I could have been the boy with the scooter and therefore feel qualified to answer.
“Where are the electrical vehicle charging points?”. Nowhere, but they would not be evident today either. However the milk would be delivered on an electric float, having recently replaced the horse and cart.
“The ice cream van appears to be polluting, contributing to childhood asthma and the ice cream to obesity.” The ice cream van came down our road only on weekends and was one of the very few powered vehicles that did. Apart from the milkman, postman and trade vehicles, only one of our neighbours had a car. So asthma due to vehicle pollution was hardly an issue. As sugar was rationed until 1953 and families were living in post war austerity, childhood obesity was not a problem either. Burgers had gone back home with the US troops.
“Obesity exacerbated by lack of a local play area”. The families in the picture are enjoying a large area of grass. One child has a scooter and two others are throwing a ball. Apart from the odd swing, play equipment was rare but open spaces like this gave children as much scope as they needed for play, without the distractions of TV or computer games.
“Note the lack of any CCTV cameras”. Everyone in the group of houses would have known their neighbours by name and would have noticed anything suspicious.
“The thief disguised as a postman has targeted the postbox”. Good luck with that, there would have been nothing but letters and the odd football pools coupon with a postal order. Few people had bank accounts, there were no credit cards and bills were paid locally in cash from a pay packet.
“Where are the solar panels on the houses?”. Nowhere of course, but people used very little electricity. Fridges and washing machines were a luxury, not one house has a TV aerial and electricity was used mainly for lighting.
So maybe there was a little bit of utopia in the 1950s. And the little boy in the picture did grow up to be an engineer; the girl, probably not.
Brian Highe MIET
Cost is root of problems with LED lighting
Denis Sharp’s letter about his unsatisfactory experience with mains LED lamps in a new house (February 2014) typifies the problems consumers face when trying to make good environmental decisions. The unreliability, poor performance and suspect claims of some energy-saving products are seized upon by some groups keen to maintain older incandescent lighting.
The builder of the new house was obliged by building regulations (Part L) to install energy-efficient products. He probably chose a lamp with a cheaper price and specification and this is the root cause of the problem.
LED lighting is susceptible to heat problems and installing them in downlights is always a challenging environment. It is likely that fire hoods are above the downlights to limit spread of fire, and this also restricts any airflow to cool the lamp. I have dismantled LED and CFL lamps that have failed in this type of installation, and nearly always the control electronics have overheated. A premium product may have a thermal regulator to reduce power as the temperature rises. I have installed LEDs in completely sealed downlights and not yet had any fail.
Unfortunately, until the price of better LEDs reduces, there will remain an abundance of inferior products that remain a turn-off for consumers.
Mike Pannell MIET
The real value of managing risk
I read Derek Salkeld’s Comment column on risk management in your February 2014 issue (http://bit.ly/LWkFlX) with a degree of disappointment. He only describes a process that enables project managers to make an estimate of the value of contingency, and does not cover any of the techniques that risk managers use to mitigate the identified risks and ultimately enable project managers to make timely decisions to maintain project schedules.
He does not discuss that the real value of a risk manager is to translate the risk register from a document that merely calculates contingency to one which is reactively managed through the life of the project. By working with the engineers the impact of the risk can be assessed and its effect on the schedule monitored. This will identify dates when decisions need to be made either at a work package or programme level.
It is the risk manager’s function to run regular reviews with the work package managers to ensure that risk is being addressed and that the mitigation actions are invoked in time to ensure that the project remains on schedule. Work packages can include a risk contingency element which allows work package managers the flexibility to make decisions on mitigation and flows responsibility and accountability to individuals at lower levels. For this to work well delegations need to be made to the work package and risk managers. Too often the risk contingency is seen as margin waiting to be taken and not a source of finance that enables timely provision of mitigation.
In my experience, the project manager, particularly on large programmes, has more than enough to focus on and risk management is not addressed until something goes wrong. The role of the risk manager can therefore be critical in providing an independent view of the programme progress to the programme manager. The real benefit of a risk manager is to manage risk effectively enforcing decisions on mitigation, to help maintain on-time delivery.
Ian Griffiths CEng MIET
Capability director, General Dynamics UK
Alternative approaches to EMC
‘Screaming Circuits’ (February 2014, http://bit.ly/1nfJhS6) is a fair summary of present-day thinking on the subject of electromagnetic compatibility (EMC). The emphasis is on the use of 3D field modelling and on the convoluted geometry of the assembly-under-review; that is, on the sheer complexity of any EMC problem. There has to be a better way.
The starting point in any approach to such an analysis may be to treat every conductor as an antenna, but that does not mean it is necessary to use field-solving software.
An isolated conductor possesses the properties of inductance and capacitance. These two primitive parameters relate the voltages induced in the conductor to the energy levels of the magnetic and electric fields surrounding that conductor. Together, they allow the effect of the electromagnetic field to be analysed using circuit theory. In fact, they are two of the basic building blocks of all circuit models. In old textbooks, they are used to derive formulas for the phase inductors and the phase capacitors of three-phase power line models. A circuit model can be derived for any three-conductor assembly. Typically, these conductors would be ‘send’, ‘return’ and ‘ground’.
Such a model can be used to simulate the coupling of currents and voltages between the common-mode loop and the differential-mode loop of any signal link in the system. Invoking the use of transmission-line equations extends the ability of the model to simulate the response well beyond the frequency at which the first resonant peak occurs. This task can be carried out on critical links during the feasibility stage of a project.
Antenna theory introduces the concept of the ‘radiation resistance’. When a dipole is transmitting a signal at its half-wave frequency, the local environment behaves as a resistor in a series RLC circuit, with the L and C representing the properties of the conductor. Extending that concept to analyse the behaviour of an isolated cable leads to the idea of simulating the effect of the local environment as a ‘virtual conductor’ which has R, L, and C components.
Radiation susceptibility can be analysed by inserting a voltage source in series with the radiation resistor. Radiated emission can be analysed by calculating the frequency response of the current delivered to the virtual conductor.
Since the circuit model of any signal link is closely correlated with the physical assembly of the link-under-review, it is possible to carry out tests on that assembly using a signal generator and oscilloscope and compare the test results with that of the simulation. Mathematical software is more than capable of handling the computations. Component values in the model can be adjusted to ‘line up’ its response with the test results. At this point, the model can be used to define the EMC characteristics of the link-under-review.
Since the mathematics associated with circuit analysis is dramatically simpler than that of time-variant, 3D, field theory, the necessary programs can be compiled, run, and assessed by circuit designers.
Given the ability to create an accurate model of the interference coupling mechanisms, the engineer at the bench can rapidly gain an understanding of the phenomena. Such an understanding leads to the ability to design the system-under-review to meet its EMC requirements in a cost-effective way.
Ian Darney MIET
Dolby’s many inventions
It was beyond belief to read S Laurence Cachia’s contention (Letters, February 2014) that Ray Dolby was not an inventor. Patents are awarded for inventions, and Ray had some 50 in his name. Some of these were for the invention of the professional video tape recorder which in the form of the consumer Betamax and VHS machines changed how people watched television.
Never were pre- and de-emphasis attributed to him. As Mr Cachia points out, such techniques have been around for years - in fact well before the 1950s. However, these were almost entirely static systems and not dynamic in their operation. Dynamic compression and expansion systems also have a long history in both telecommunications and recording equipment. However all of these systems processed high-level signals which inevitably leads to audible noise modulation, transient overshoot distortions, intermodulation effects, or a combination of these defects.
Dolby’s breakthrough was to realise that noise is not a problem with high-level signals but with low-level signals which are comparable in level with the unwanted noise. This lead to the concept of two paths for the signals to be compressed (and later expanded), with high-level signals being transmitted unchanged and low-levels passing thorough an independent processing channel. This invention, awarded a patent in the mid-1960s that has never been challenged, solved the defects mentioned and was the basis of his first products which almost immediately resulted in the demise of the many traditional noise-reduction systems and became a standard in the recording industry. Truly an invention.
Other inventions followed, in consumer analogue products and then in digital signal processing, all awarded patents, and many being adopted by the industry since they were markedly superior to existing technologies - and perhaps more importantly, could be seen and heard to work due to their radically different ideas, whereas others had significant flaws. It is a measure of their inventiveness that so many of today’s professional and consumer products, which are part of our everyday lives, use his inventions.
David Robinson CEng FIET
Sebastopol, California, USA