Member postings for SillyOldDuffer

Maybe there's some sort of comfort in that, but the all important financial numbers tell a different story!

Measured in Gross Domestic Product per working hour, British productivity has long been lower than that of similar economies. In the 2019 league table, Britain is 20th, with lower productivity than the USA, Canada and the rest of Europe. Not clear yet what Brexit has done for productivity, but so far leaving the EU has damaged rather than improve the UK economy.

Britain's relatively low productivity is despite considerable improvements in recent times. It was even worse in the good old days - UK productivity increased x2.5 between 1970 and 2015.

My advice: never believe your own propaganda! Faced with reality, it's unwise to take refuge in comfortable generalisations. Instead, get to work. Find and make immediate improvements and plan to make more in the future. Never assume that what worked well 50 years ago has any value in 2023!

Whenever Mr Foreigner does better than us, it's our job to get our act together and overtake him. Relying on comfy generalisations is unlikely to help.

Dave

When replying to adverts don't delete the words automatically added by the forum. At first glance they may look like unnecessary small-print, but they contain your return address. It's essential!

Dave

Just a guess because the description of Robin's Sealey lamp doesn't say so, but it claims to operate from a 10V to 30V DC supply. The input voltage range implies the lamp contains a some sort of electronics, perhaps a constant current power supply, in which case it may not need any smoothing at all.

My main concern with powering it from 24VAC and a rectifier is that the peak DC output is nearly 34V, which might result in the lamp having a short life. (The blurb says 10V to 30V, not 10V to 36V)

Unfortunately the spec doesn't say how much current the lamp draws. However, 27Watts is probably the light equivalent, not the actual power consumption. As LEDs are abut 10x more efficient than Halogen, I guess the lamp consumes 2 or 3 watts, say 100mA, not enough load to stop a beefy 24VAC supply rated to run a halogen lamp charging a big capacitor up to 34V.

The lamp costs £18.60. I'd either:

• Be a cowardly lion and run the lamp from a 12V supply, or,
• Assuming 100mA is about right and, add a 56 or 63ohm 2W dropper resistor. This would take peak volts down below 30V
• Try the lamp on 24vac (or via the dropper). with no capacitor. If it works without flickering, down tools. If not, try adding a capacitor, something between 470uF and 2200uF. Having an oscilloscope means I could measure the ripple voltage and calculate the correct value, but I suspect it's not necessary. Suck it and see.

How long a slightly over-volted LED lamp will last is anyone's guess: I suspect it will be OK. As the lamp is moderately expensive, I'd fit a dropper resistor.

This stuff is much easier if you have a mutlimeter and oscilloscope because a few simple measurements remove most of the guess work.

Dave

An interesting development this afternoon! I found a code error. The standard deviation of my data isn't about 1mS, it's 0.037 milliseconds, which by SK's method above gives my pendulum Q=13500.

Sorry about that, my fault.

Assuming the data and method I'm using is correct, which has been strongly challenged by John, the 3db bandwidth of my pendulum is about 0.044 milliseconds, period 0.937357s.

Dave

Oh dear, a major breakdown of communications! No wonder - it's getting complicated,

My Graphs 3 and 4 are examples illustrating how the shape of a universal resonance curve depends on the damping factor. They're a response to John's post in which he compares a normal distribution curve to a resonant curve and suggests the curves move away from each other. I'm pointing out by example that the shape of a resonance curve can be made to look like a normal distribution by tweaking the decay factor. I said I don't believe it proves anything!

This part of the discussion relates to a serious criticism John is making of the way I calculate Q-factor using what I believe to be the valid bandwidth method. Serious because I'm an amateur poking around in the dark, whilst this is John's area of expertise and he can do the maths! At the moment I'm in the unhappy position of not understanding my own work or understanding why John thinks I've got it wrong.

My efforts this afternoon have shown my pendulum's frequency distribution is close to a normal distribution and that I can synthesise a resonance curve to take much the same shape. I'm no nearer proving to my own satisfaction that the way I calculate Q is right or wrong. Sadly, when an expert tells an amateur he's messed up, the expert is usually right...

Dave

An LC circuit of the same Q and resonant frequency as a pendulum would take the same number of cycles to decay and hence the same time.

The decay formula is :

However LC circuits usually oscillate at much higher frequencies than pendula, so the number of cycles needed for an LC resonator to decay to the same level occur much faster, An oscillator of Q=10000 at 10MHz decays 10 million times faster than one of Q=10000 oscillating at 1 Hz.

Dave

No point in denying it - I'm worried, and have been since John emailed a couple of his papers to me last week . Not quite convinced myself yet I'm wrong about Q but I trust John's judgement in this area. So I spent this afternoon bashing my brains in hope of understanding it!

Doesn't prove anything but I produced these similar graphs, also comparing normal and resonant curves:

First up is my pendulum's frequency distribution.

Second is my pendulum's frequency distribution fitted to a normal distribution. The match is good suggesting my pendulum is producing normally distributed periods.

Third is a resonant curve generated from this formula found under 'Universal Resonance Curve' in Wikipedia's Resonance article:

ω is the natural resonant frequency
Ω is the drive frequency
Γ is the decay factor

Damping the third curve with a decay factor of 0.1 produces a curve similar to the actual pendulum distribution

Fourth graph is the resonance curve generated with a lighter decay factor. As expected it produces a much sharper curve.

No wonder I'm confused!

Dave

Um, 12 threads on half an inch is 24tpi. but how accurate was the measurement? As M8 x 1.0 (fine) is equivalent to 25.4tpi and M8 x 1.25 (coarse) is 20.32 tpi, the measurement has to be good.

This motor comes in many variations, and although I found two specs saying M8, yours could be UNF for the USA market. If M8 it's more likely to be coarse than fine.

How sure are you of the test nut? Perhaps it's not M8!

Check both motor and nut threads for damage - dinged threads struggle to mate.

I'd try gently running the M8 coarse die down the motor spindle. Don't force the die in case it's a poor fit or the spindle is hardened. If the thread is only damaged the die will clean it up. With more energy it might also convert 24tpi into a usable metric M8, but the thread will be mangled and weak - too much of a bodge for me.

Dave

Unfortunately the forum software doesn't allow ordinary members to rotate their own photos. Only a moderator can do it, and only to copies of photos in posts. not to originals in an album.

The restriction is probably because twirling photos is slightly dangerous - sometimes it upsets other formatting as well, which can be hard work to disentangle. I rotate pictures whenever I see them unless pressed for time and can't afford to spend 10 minutes sorting out a mess in the unlikely event it goes wrong.

Root cause is digital cameras have several ways of deciding which way is up, and these are recorded in each photos metadata. Display software sometimes chooses inappropriate metadata and renders the image wrongly. The forum and my Canon camera always get it right, whilst the forum and my Sony get about 10% of photos wrong. I don't know why.

The only sure fire way of guaranteeing orientation is to manually edit images with a photo editor. A human saying 'this way up' must have priority over other methods.

It's a pain. Work is in hand to replace the forum software; fingers crossed the new forum will always get images right, and allow ordinary members to rotate their own photos.

Dave

Edited By SillyOldDuffer on 18/08/2023 13:03:42

Not exactly a clock, but this video of Adam Savage looking at a fake Perpetual Motion machine at the Royal Society is interesting.

Cheap versus well-made drills like Dormers are difficult to compare because so much depends on how they are used.

Industry, especially manufacturing, put a lot of effort into getting the maximum value out of cutting tools. One way of doing this is to buy reliable cutters and operate them within tightly specified limits. Running within specified limits allows tool life to be measured and compared with tool-cost. Many factors apply, for example it's probably not worth buying best quality to drill a few low tolerance holes in soft metal. Down-time due to tool changing is often a major expense. When usage is controlled, it becomes obvious whether more expensive high-spec drills are worth the investment, or it's cheaper overall to buy middle or low-specification drills. In industry, it's all about money!

Jobbing workshops, and especially hobbyists, work in ways that make it difficult to assess tool life. Typically, the same drill is used on different materials, different thicknesses, different machines, with and without coolant, by an operator working at different speeds. The work can be abusive, for example drilling thin steel-sheet without a backing, struggling into work-hardening stainless, by pushing too hard, not clearing swarf and many other faults. Much depends on the type of work being done: in my rough workshop, it makes sense to buy inexpensive mid-range, and treat twist-drills as consumables. When better is needed, I buy one in specially and look after it. Others work in ways where it makes sense for their tools to be well-made and looked after, only buying cheap on special occasions. After several years I suspect most hobby workshops end up with a mix of inexpensive tools for rough and a selection of better tools only used when better is really needed.

Eclipse is a trademark. It was registered by James Neill and Co (Sheffield) in 1909. Neill were a major player in steel-making and tools, absorbing other famous firms like Moore and Wright as they grew. In 1985 Neill bought Spear and Jackson, and in 1995 renamed the whole company Spear and Jackson. In 2014 Spear and Jackson were bought by SNH Global Holdings Ltd. SNH describe themselves: 'SNH has become a global business. With a historically strong presence in China and the UK, we have extended our operations into other territories and now have manufacturing sites, distribution centres and sales offices in key locations around the world. Each of these divisions operates autonomously within the Group. This autonomy, we believe, encourages management independence, entrepreneurism and ownership.' List of companies here.

As is the case with multinationals, products are made wherever in the world it happens to be most profitable.

I'm pleased to say UK Engineering is holding it's own. The value produced is about the same as it ever was. True that large numbers of firms making ordinary products went to the wall, often in a sad welter of mismanagement, poor labour relations and low productivity. Unfortunately lots of interesting jobs went too - agonising. Surviving firms moved up-market, and mostly only make expensive high-end products. Rather than lots of old-fashioned firms scratching a living making pots, pans, and pen-knives, the same money today is earned from high-tech - MRI scanners, aerospace, and electronics etc. British Industry and the character of the workforce has changed, not disappeared, and it's globalised. Difficult to buy anything these days and be certain it was specifically made in one country only. Designed in the West, made in the East is a common pattern, and quite likely an international holding company has a head office in Lichtenstein, banks in the Caymans, is registered in Switzerland, trades on the London Stock Exchange, and pays tax in Eire! Though it makes us rich, I doubt it's a good thing in the long run.

Dave

I am using the 'simplistic formula' for bandwidth. As far as I know it is valid - it's in all my books! Do you have an alternative?

The diagram is from a Radio Communications Handbook, where Q= 500 is about right for an ordinary inductor/capacitor resonator at radio frequency. It doesn't represent the Q of a pendulum, quartz crystal or anything and else, just the typical shape of a resonance bell-curve.

It's how narrow the curve is at the 3dB down points that decides Q. In the example below, all three curves are of the same form but Q=1 results in a low hump, whilst Q=100 gives a sharp peak:

As I said to John in a related thread, the Q calculation I'm using reports period consistent with the physical length of my pendulum. If the calculation gets period right at the 50 percentile, why should it be wrong at 70.7 and 29.3 percentiles?

In an earlier post you said applying the bandwidth method to your pendulum gave Q=190,000. Can you share the data and calculation please, showing working. Might highlight what I'm doing wrong!

Though related there's a difference between Q and standard deviation. In my simple view Q is a measure of how much energy is needed to drive a pendulum, whilst standard deviation is a measure of the pendulums frequency stability.

I'm not too worried about by pendulum's high standard deviation because I've not found any evidence, yet, that it's related to the rate wandering. At the moment the clock is 14 seconds out in 2,835,926 which is 4.9 parts per million, so not disasterous. What's worrying me is the rate isn't altering at a steady rate, or changing with temperature or pressure. I'm letting it gather more data in hope a pattern emerges.

Dave

I can't find any tolerances for Bright Imperial Round Drawn under 1/2" diameter, which is -3 thou to 0.0

Bright Metric Round Drawn under 6mm diameter should be -0.07mm to 0.0

What you have is certainly in spec for metric 3mm, and given Imperial doesn't seem to specify tolerances below 1/2", it could be street 1/8" too! Bet its 3mm though.

Dave

Dave

OK, but what am I measuring then?

In my set-up a crystal oscillator measures the period of each beat of a pendulum, outputting a long list of similar values, standard deviation about 1mS. Averaging the list gives a value, 0.933558s, which is close to the period predicted by the usual formula from my pendulum's length. Further, plotting the distribution of periods from the list gives the bell curve expected of an oscillator.

If the peak of my bell curve gives the pendulum's correct frequency, why don't the 3dB points on the same curve give Q?

As period and frequency are equivalent, I think my data represents a spectral distribution. I'm not understanding why it's different from a resonant curve.

Gosh my head hurts!

Dave

Last night's exciting episode ended with our hero (me because I'm writing the script) assailed on all sides. By analogy I was cuffed inside a heavily weighted crate dropped into the Atlantic north of Scapa Flow. Fortunately I'm a pulp fiction fan, where cliffhangers are resolved in the next issue with the line 'With one mighty bound he was free."

Oh well, back to the real world where I may be sunk without trace!

SK repeated my description of the bandwidth Q-factor calculation on his data and got an absurd answer. I don't think that proves the bandwidth method doesn't work. I'd like to run SK's data through my program to see what I get. If I get 198,000 too, then the clearly my approach is wrong. Any chance of making the data available via Dropbox or similar?

John Haine is more difficult to deal with because I'm well out of my depth with the maths! John said (full post above at 17:32 yesterday):

It seems to me that the resemblance of the normal distribution curve to a resonance curve is tempting but unfortunate. Assuming that Dave's period distribution is normal, its width is characterised by just one parameter, the standard deviation. The "-3dB" points are related to this but superfluous.

In practice the width of the period distribution must depend on the amplitude and noise level (i.e. the "signal to noise ratio" as well as on Q. So buried in Dave's computation is this SNR, which itself is also determined by Q (as this determines the bandwidth of the noise which is affecting the period).

In response, I didn't invent the Bandwidth method of determining Q-factor!

As I understand it Q-factor is a dimensionless indicator of the goodness of an oscillator. Any oscillator from bouncing balls to atomic clocks. To my mind a pendulum is just another oscillator following the same rules as all the others. Oscillators resonate at a particular frequency, and energy is required to keep them going. Lossy oscillators, such as a pendulum in treacle, have low Q because stirring treacle consumes lots of energy. The same pendulum swinging in a vacuum has high Q because atmospheric friction is eliminated. Exactly the same rules apply to Inductor(L) / Capacitor (C) oscillators. Although capacitors are low-loss, the inductor is a metallic wire coil and the wire is a resistor. The same inductor made of Brass wire has lower Q than one made of Copper, and Silver is better again. Energy loss in a resistive inductor behaves the same way as energy loss in a pendulum overcoming air resistance.

Two ways of measuring oscillator Q:

• Impulse the resonator once and count how many cycles it takes for the amplitude to decay by a known amount, say 50%. Q is calculated by applying a formula. This is the decay method
• Impulse the resonator to keep the resonator running continually. Amplitude peaks when the impulse frequency matches the resonant frequency. In practice the resonant frequency varies about a mean, and it has a normal distribution. When a lot of energy is needed to maintain oscillation, the resonant frequency also varies a lot - low Q. When very little energy is needed to maintain oscillation, frequency doesn't vary much. Q is calculated by determining the resonators bandwidth by getting the frequency spread by analysing a large number of periods. Narrow bandwidth means high Q, wide bandwidth means low Q. Q is calculated by applying a formula, this is the bandwidth method.

John said: 'seems to me that the resemblance of the normal distribution curve to a resonance curve is tempting but unfortunate. I disagree - I think the resonant curve of an oscillator is normally distributed unless something disturbs it. Standard Deviation isn't the whole story because, as far as I know, it doesn't describe the shape of the distribution, narrow or wide. Stdev has a dimension, whereas Q is dimensionless.

I can't argue with John's formula, but offer this from an article on the web:

This formula doesn't introduce the spectral density of the noise force component of the impulse.

Duncan suggests measuring my pendulum with both decay and bandwidth methods. Did that in the past and got a result within about 30%. Not conclusive because I didn't repeat the measurement several times. Can't do a decay measurement on my clock at the moment because it's doing a long run. For family reasons I'm short of time at present, but might find a few hours to hack a test pendulum. Alternatively, if John has decay measured one of his pendula, and has a run log, I could analyse that to see if results are similar.

Though chest deep in doubt, I still think Decay and Bandwidth are both valid ways of measuring pendulum Q.

Dave

After reading SK and John's posts I decided to pour myself a couple of large sherries and go to bed early!

Dave

Only at high-speeds is consistent with over-filling, if that might have happened during maintenance. Or maybe Bearing 127 has an oil seal on the inside that's failed - replace bearing.

I don't have a gearhead lathe, but Samsaranda's post makes sense to me. Gearboxes don't like being overfilled.

Dave

I'm surprised what I said is controversial, hey ho such is life!

My point is three-fold: the formula is an approximation; it assumes the test pendulum exhibits damped harmonic motion; and results depend on the ability of the observer to measure amplitude accurately, which is hard. (Of all the ways discussed on the forum I'd expect your capacitive system to be the most accurate because it eliminates the human element!) I suggest this combination of factors creates a situation in which forum members report different values of Q.

Although the Q formula we're discussing is scientifically derived, it's simplified. Many others are in the same boat: Ohms law doesn't apply to substances with negative resistance, and it only applies to DC or pure resistances; Newton's Laws are inaccurate at very high-speeds and below Atomic scale; the standard pendulum formula is a simplification, only accurate over small arcs.

I absolutely agree Q isn't the final cut!

I disagree that Q is Q. In electronics, there is unloaded Q, loaded Q and coupled Q. An electromagnetically impulsed pendulum, or one attached to an escapement, are both loaded. More importantly, a mechanical system has more disturbances than an LC circuit. As Duncan says, opening the door of a pendulum case alters Q because the air eddies around the bob will be different. Impulsing also disturbs the pendulum mechanically, in an extreme case by whipping the rod. Therefore, so I'd expect my pendulum kicked by a single pulse to have lower Q than it would with a well-adjusted sinusoidal drive.

So I see Q-factor as a useful guide rather than an absolute measurement.

When your pendulum is running and logging data, it will be easy to calculate Q from bandwidth periodically. Try it and see how it compares with my results and the lost energy calculation. Whatever it is, I'll be amazed if your pendulum doesn't keep better time than mine.

I suspect we're only disagreeing about the size of the Q ball-park! One thing I've learned in my pendulum adventure is that measuring anything to do with precision clocks is tricky.

Dave

It's not meaningless in a different way. Rather a lot of British Law is vague, not black and white, and it's left to the courts to decide what it means. Anyone likely to end up in the dock needs to think about their liability in the event of an accident.

Put yourself in the position of an employer faced with: "No person shall be engaged in any work activity where technical knowledge or experience is necessary to prevent danger or, where appropriate, injury, unless he possesses such knowledge or experience, or is under such degree of supervision as may be appropriate having regard to the nature of the work". Thinking of saving a few bob by paying a 12 year old boy to upgrade all the fuses in a 415V switch-room? If so, consider what a Judge, Jury and Insurance Company would make of your decision it was appropriate for a child to do the work. Same applies to telling apprentices and other staff to tackle jobs outside their experience: if there's an accident, you could be found responsible. Gaol, fines, bankruptcy, reputational damage etc.

In this example, to avoid legal unpleasantness, employers have to be able to show that the Electricity at Work Regulations were applied responsibly. In the event of a prosecution how that's proved is down to the employer, but it helps to prepare in advance. Being able to show he employs people with paper qualifications, or relevant experience, and then provides training, suitable supervision, risk management and is health and safety aware goes a long way. An incompetent employer who used untrained staff to take ill-considered short-cuts and hasn't done anything to protect himself and his workers deserves all he gets.

It's an imperfect world. A certificate proves training was undertaken, not that the holder will apply what he learned. However, in the event of an accident, the employer is off the hook, and the man who failed to follow his training is in trouble.

I'm in two minds about whether or not blurry law is a good system. Doesn't help anyone who expects to be told exactly what's right and wrong in simple plain terms! Most people assume rules will be clear. Bad employers can get a good lawyer and argue the toss, often getting away with murder. Responsible employers apply it sensibly, achieving competent safe working by applying any of the many alternatives that best suit their circumstances. The assumption is most employers are responsible, and don't need to be inspected or policed.

Dave

Edited By SillyOldDuffer on 16/08/2023 19:42:17

Rawlings in 'The Science of Clocks and Watches', spends Chapter 4 on 'Dissipation of Energy by a Swing Pendulum'. He addresses the amount of energy needed to keep a pendulum swinging, but doesn't relate it to Q, which was new to clocks when he wrote circa WW2. Rawlings measures the decay of an actual pendulum and graphs it, Then from the graph he derives an equation that's a close match to the curve. The formula uses e (Naperian Log) and a constant of 16.6e10-5 per second; "chosen to make the curve pass as close to the squares as possible".

The 3rd Edition of Rawlings (1993) was updated and annotated by several up-to-date contributors, notably D A Bateman, who introduces Q. He mentions Drop until 50%, then x 4.53 as a way of estimating Q and explains that it and Joe's other values derive from the Naperian Log part of the equation. which assumes the pendulum exhibits 'damped harmonic motion', in much the same way as an early spark transmitter. DAB extends the maths in Appendix 2 'The Linear Theory of Vibration', which finishes with:

• The logarithmic decrement leads to an easy rule of thumb for measuring Q.
• Then: Q = πn/ln2 = 4.532n (approx) and
• With the low frequency of a second pendulum, this may entail waiting for an hour or more , but the calculation could hardly be simpler.

But I suggest there are several ways in which the formula could give wobbly results! For example, when a pendulum swings through a tiny arc, how accurately can the observer judge when 50% decay has occurred? And does he know that his pendulum is following 'damped harmonic motion'.

Unless the measurement is made very carefully in the same way by all parties, I think it unwise to get excited comparing the Q of other folks pendula. However, when the same method is applied consistently by the same operator, Q is useful as a way of checking whether a modification has improved or made a pendulum worse worse.

As a self-check, if the values of Q measured in the same run at 21%, 36%, 50% and 63% are wildly different, it's likely that the operator is doing it wrong, or that the pendulum is wonky, or both!

My method of deriving Q from a bandwidth formula has other problems. It assumes that the values of a large set of frequencies are normally distributed. This way of obtaining Q doesn't assume a logarithmic decay, which is just as well because my pendulum is being impulsed: definitely not 'damped harmonic motion'. And I'd expect the Q of a powered pendulum to be different from the Q of the same pendulum left to lose energy naturally. Nonetheless Bandwidth Q is meaningful to me because exactly the same method is applied every time I log new data, and I can trust it in my context. It's not necessarily useful to anyone else unless they use the same method.

Measuring is hard!!!

Dave