Tim Jackson
I am a Reader in Electrical Engineering, teaching electronics and electrical machines and supervising student projects. I also work in the planning and design of engineering education.
Location United Kingdom
Activity
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Tim Jackson replied to Dominics Akahan
Not an essential pre-requisite, it depends what you wish to do. Sometimes we only need very little power from a sensor in which case ensuring you get optimum voltage transfer is best. To do that, you want the input impedance of your amplifier to be much greater than the output impedance of the sensor.
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Tim Jackson replied to Edward Wright
Yes that method helps with management of the flow of people, but would be hard to fit retrospectively on an underground line.
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Tim Jackson replied to Dominics Akahan
And when it does work - nobody notices!
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Tim Jackson replied to Cedrick Kileta
The volt amps thing comes into play with AC power, certain types of motor are a good example. The current supplied has to provide power both to do work and to set up the magnetic field. The magnetic field energy is "borrowed" in the sense that when the motor is turned off, the magnetic field collapses and the energy flows back to the source. But in use we have...
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Tim Jackson replied to Eduardo Romani
What gives it away Eduardo?
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Tim Jackson replied to Cedrick Kileta
Do you know the reason why power ratings are given in VA?
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Tim Jackson replied to Dominics Akahan
When I first came across this example I was struck how many different physical processes have to be considered. It makes for really interesting projects.
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Tim Jackson replied to Dominics Akahan
Please follow the link
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Tim Jackson replied to Phil Thress
Resistance is the ratio of voltage across something to the current through it. We are often told that it is a measure of how much a material opposes the flow of current, but that definition leads to confusion. There is no opposition to the flow of current in a wire. The amount of current is determined by the properties of the metal and the length and diameter...
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The resistors are needed to get the chip to amplify the signal. We have to choose the values to get the size of output signal we want. Impedance matters because it affects the power transferred through the system. Imagine you are in a room and you start shouting. Because the walls have a different impedance to the air, your shouts get reflected back to you...
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Tim Jackson made a comment
Would anybody like to help Phil?
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Tim Jackson replied to Dominics Akahan
This is an excellent example of how we tend to take engineering for granted. Stuff works, so we don't think about it.
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Tim Jackson replied to Dominics Akahan
That's true - connecting things together requires consideration of the input and output impedances, if we wish to transfer maximum power for example. Put a short circuit on the output of many electrical systems, to take an extreme example, and you may be in trouble!
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Tim Jackson replied to Dominics Akahan
That's very well put, thank you.
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Tim Jackson replied to Simón Jiménez
I would say yes - an actuator that is driven by an electric motor to create movement is converting electrical energy to mechanical energy (probably with a magnetic field as the intermediary).
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Tim Jackson replied to Volodymyr Voytenko
Yes, and you can use a loudspeaker (or at least the principle) backwards as a microphone
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I'd say it is where you convert energy from one form to another in a small scale for use locally. A very old fashioned example would be a dynamo to power the lights on a push bike. There are many more modern examples - could you use the movements of your running shoes to charge your phone for example? The challenge in such applications is to convert energy...
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Tim Jackson made a comment
In the past I've had students take computer keyboards apart. it's really interesting to see how the mechanical design of a keyboard can be used to give effective feedback on the data entry process. of course you can't check the that the data makes sense but you can confirm that data was entered through the feel and sound of the keys. You can also see how the...
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Tim Jackson replied to Phil Thress
The output of a sequential logic system is determined by both the present values of the inputs and sequence of events that led to those present values. Is that better?
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Tim Jackson replied to Vishnudutt Kaushik
In my teaching I try not to use the phrase "opposes the flow of current" because all conventional electrical conductors have some resistance. Without the conductors, wires etc, there would be no current flow. So I think it is better to interpret Ohm's law in this way: The resistance of a component determines the current that flows from a voltage source. Or if...
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Tim Jackson made a comment
A lot of excellent ideas here. John's suggestion of the Futurelearn course as a system for learning was wonderful; you're all providing inputs and processing each other's inputs. Sometimes another learner evaluates and provides feedback on your input which leads to a refinement of everybody's understanding as an output. Comparing all the examples, we can see...
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Yes, that's a good way to put it.
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I think this is a useful way to look at what we design. Often we expect our technology will act in accordance with the way we think. When we come across something new, we may have to re-evaluate - we have to learn. A really novel product inspires us to learn and be able to do things we never expected or imagined. On the other hand, a product that confounds our...
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Thank you Shareef for helping out your fellow learners
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Yes, it helps to know what people are talking about in all branches of engineering.
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That's where I started too, there's lots more to the subject as you'll see
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I hope you enjoy the course.
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Tim Jackson replied to Matt P
There is a type setting error in the speed, which is 10(6) m s-1. Then the calculation of the current density is correct.
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Tim Jackson replied to . alanh .
Alan, thank you for your feedback about this.
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Tim Jackson replied to Renate R
Thank you Renate, I'm glad you have enjoyed it.
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Tim Jackson replied to paul o'dee
Thanks Paul
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Tim Jackson replied to john o'brien
Thank you John for adding a lot of contextual information to the course. It has been interesting to me and I'm sure to others too to hear your thoughts. We hoped to show Engineering as something that happens in society, that is done by people and that has impacts on other people; we didn't want to just cover some technical material. Your comments make me think...
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Tim Jackson replied to Robert Walker
We often say to our students that the way they learn, and how to learn, are as important as what they're learning. I pointed out to some of them that they'll still be working in the second half of the 21st century - I'm not sure they all liked that message!
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Tim Jackson replied to Paul Smith
I did guess you had some experience!
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Tim Jackson replied to Kathryn Merrett
That's good to see Kathryn
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Tim Jackson replied to Martin Jimenez
Yes, too short. There's so much we could have done.
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Tim Jackson replied to Chris Cussen
I'm glad you enjoyed the course Chris, and thanks for your feedback
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Tim Jackson replied to Jonatan Garcia Altamirano
The more you look into these things, the more amazing they seem
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Tim Jackson replied to Jovanny Martínez C
That's good to see Gustavo
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Tim Jackson replied to Stuart Emmett
I'm glad you've enjoyed it Stuart
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Yes, and system failure should lead to a safe state
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At this stage it is interesting to go back to what we all thought the system should achieve. Are we meeting those requirements. Are we giving enough information to all the users?
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Tim Jackson replied to Kathryn Merrett
When writing this section, I found it useful to write down exactly what we wanted to achieve in short phrases expressing one idea at a time. Such phrases often match to the definition of one of the logic gates.
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Tim Jackson made a comment
There's a clear consensus among your responses on what factors need to be considered. The activities coming up will pick up on some of them. You may have noticed that shield walls are most common in metro and underground systems, where crowding is quite common. On conventional train routes most of the time (in my experience anyway), crowding on station...
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Tim Jackson replied to Terry Tyson
Terry you're right, 1011 isn't correct, it should be 1001
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Yes, it should be 25 A, thanks for spotting this one
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I think that's a nice example
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For input, if you press a key and the system beeps, you know it has received something. Real-time feedback to the user is important.
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"Gulf" means a gap. So we are referring to a gap, or absence, in our knowledge of what information the system has received from us, or what the system has done.
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Tim Jackson replied to William Rice
Eddy was right, strictly speaking power is the rate of movement of energy but much of the time we use the terms interchangeably. I tend to avoid saying "generation of electrical energy" because energy can't be generated. So I prefer to refer to generating power and to power as an input, although if you split that down into "input of rate of change of energy"...
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Yes it is a typo, sorry everyone and well spotted!
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Have you tried downloading the video?
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Tim Jackson replied to bill hood
The main function of the pre-amplifier is to separate the sensor from the rest of the system. The cable from the sensor to the amplifier has its own capacitance which will become an electrical load on the sensor. So it is best to mount a pre-amplifier right next to the sensor. The pre-amplifier then "drives" the signal on the cable. The cable between the...
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Tim Jackson replied to Robert Walker
Yes, we teach the op-amps first as once you have the design principles in mind there's much less to worry about than when designing with discrete components. Valves and transistors are a lot more challenging. For this project, the op-amp is fine because we don't need to generate significant levels of current and it has the advantage of a very high input...
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Tim Jackson replied to paul o'dee
That's what my students at the University said last week too!
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Tim Jackson replied to Angel Caliwag
From the colour coding
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The epoxy must make some difference to the response, but there is still plenty of sensitivity. It will load the sensor, and affect the frequency response, but I haven't investigated much it difference it makes. Some people use piezoelectric polymer foils instead of ceramic discs, which will have a different frequency response altogether. Whatever you use...
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Tim Jackson made a comment
This week we have thought thought about electrical systems and formalised the ways in which we describe them. The application of definitions is not always straightforward. We have to think very carefully about our use of language in order to express our ideas clearly and unambiguously. We saw this in particular when we tried to distinguish between sensors and...
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Tim Jackson made a comment
The discussions this week raise some interesting points. First of all, it can be quite difficult to decide where the boundaries of a system are. Secondly, the separation of the various processes - input, processing, communication etc - is sometimes a matter of choice and convenience and can come down to function, for example an antenna could be the input...
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Tim Jackson replied to John Mallett
That's interesting. It is done - some pressure sensors a metallised diaphragm as one plate of a capacitor, which sounds very like what you are describing. In that case there isn't any energy conversion in the unit itself.
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Tim Jackson replied to Mohamed Shawky
There's power too- from the food we eat, and communication via the nervous system as well as storage in memory
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Tim Jackson replied to Kathryn Merrett
Dear Kathryn, that's good to hear thank you. We wanted to surprise people a little if we could.
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Tim Jackson replied to Paul Crooke
Paul we had some problems with this question I'm sorry to say, we sorting them out now
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Tim Jackson made a comment
I'm struck that some of you mentioned it would be better if you understood what your computer is doing, or how it works. A system designer should assess the state of knowledge of the users, and then design feedback on their actions on the system so that the user is sure (i) that the data they input was what they intended, (ii) the processes that have taken...
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Tim Jackson replied to Fahad Alzahrani
In this case we input the operation signs and the point at which to stop calculating. That then provides a trigger for the system to calculate and display (output) the answer. So I'd say the numbers, equation and equals sign were all inputs.
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Tim Jackson made a comment
A lot of imaginative examples here. I agree with most of them. Certainly a system can either be something that people have made or something that occurs naturally. We do need to be careful to distinguish between a system and a process (a series of actions). Perhaps you can see what I'm referring to in these suggestions?
