MEW 253: Workshop Techniques; Darren Conway

Interesting stuff, but I think the lack of proof-reading &/or printer's errors have let the author down. It's good to see this sort of article in the mag, rather than the all-too-common picture-heavy 'Wot I did on me 'olidays wiv a welder/angle-grinder/'eavy 'ammer' type of article that is not very enlightening.

An explanation of the maths in Table 1 would be appreciated - there are undefined variables, and the formulae are truncated. I suspect there should have been a diagram to accompany the table. Also, I'm sure it's just a slip: RMS calculation (as used for the total error calc'n) requires the root is taken of the mean of the squares, not their total.

Well, he could have divided the answer by the square root of the number of measurements but he seems to have forgoten to do that.

Russell

Ouch!

I hadn't picked up on the table columns getting cropped.

You will appreciate I generally don't have the capacity to work through the maths when I get articles, but I should have noticed the cropping.

Neil

Neil.....with respect Kiwi Bloke is suggesting a little more than truncating/cropping. If an article is complex

1 do not print the article

2 have the article checked by a competent third party

Given that there was no great clamour as to errors by subscribers,perhaps the article was too complex for the average reader. And there's me thinking computers solved the worlds logic problems!! But then Kiwi Bloke could be wrong?

Mr Stevenson...... There are those on this forum who THINK they know everything much to the annoyance of those that DO. My only concern is presenting the truth in a manner that is decipherable to those willing to learn

.

... But they only see the text after publication.

Admittedly, it does seem that some of the tool suppliers let the customer do the quality control; but it's not really an approach to be encouraged.

MichaelG.

To be fair, it's not a learned journal that needs peer revue.

Russell

Learned Journals need peer revue, Russell, because readers are going to rely on the information. If we are not able to rely on the information in MEW (or ME - just as wobbly) then what is the point of it?

Regards, Tim

I haven't read the article but it sounds like confusion between RMS and RSS .... e.g. here.

There is no simple answer.

I don't have the budget to get someone to check every article that has a formula in it. Indeed we don't even have proof readers these days. Publishing is a very 'skinny' operation these days.

Sometimes I do get things checked, but only in extremis. The main reason for this is that there are usually only a few days available for such checking.

The other alternative is simply not to publish any article that I am not able to 100% check myself or that I don't agree with 100%. This would make MEW a very thin and boring magazine...

I must admit, I put a lot more effort into trying to get my head around the calculations for the Jacob's Hobber - I failed to get past grasping the basic principles; I saw Darren's article as largely about technique and his 'error budget' was just incidental to the whole so I gave it less attention.

Neil

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You have my sympathy, Neil

... and I think Russell's comment sums-up the situation nicely.

MichaelG.

My sympathies are with Neil too. Proof reading is difficult and time consuming. As it's also hard work I don't think I'll be volunteering.

I find much of interest in MEW and ME and quite enjoy spotting the boobs. Safety issues apart, the mistakes rarely matter much. After all, only God is perfect.

Dave

Edited By SillyOldDuffer on 10/04/2017 20:09:44

I haven't read the article yet as I get put off by too much maths, except as Neil says for the occasional thing that intrigues me like hobbing and dividing calculations. However picking up on an earlier post about RMS if errors are being analysed then RSS (Root Sum of Squares) may be the correct technique not RMS. I used to use it a lot in the days before we had computers ie by long hand for understanding errors in microwave equipment design. Sometimes took an hour to run a calculation that is now done in seconds in excel.

RSS is used for variables that are vectors - effectively it is equivalent to calculating the hypotenuse of a triangle formed by two vectors. Apart from electrical power of pure sine waves I'm not sure when RMS is appropriate.

.

Maybe worth noting that RMS is essentially the same thing as Standard Deviation ... which broadens the field of relevance a little.

MichaelG.

[time for bed now]

Oh, wonderful! This is why this forum is solid gold. There's so much knowledge and wisdom around. Thank you Bandersnatch and Bazyle! It has to be RSS, doesn't it? I found physics, pure and applied maths fine, but statistics and probability calculations caused cerebral meltdown. Why are they so counter-intuitive?

Neil, just getting the mag out regularly must be a nightmare. Well done! Unfortunately, as editor, you get to be the focus of all criticism, discontent, etc., whether deserved or not. Perhaps the occasional praise, if you're lucky, makes it all worthwhile. Proof-reading must be a dying/dead art - or just too expensive. Spell-checkers are no substitute. I have the unfortunate ability (disability?) to spot typos and similar errors almost as soon as I turn a page - except in my own writing, of course... It was useful, professionally, but it's a pain. I also wince when I see misplaced apostrophes. I'm glad to see that MEW is better in this regard, under your stewardship.

Whilst MEW is not a learned journal, it aims to be instructive. Let's hope it retains that aim, and doesn't degenerate into a colour-glossy entertainment rag. It has a responsibility to print correct information (wherever possible). That's a big ask.

I think RSS applied in this situation.

My understanding is that it applies when the cumulative effect of several uncorrelated errors is being estimated, rather than multiple instances of the same error.

Neil

MEW is written almost entirely by its readers, rather than by 'experts'; this has pros and cons!

Apostrophe's? One doe's ones best.

Neil

The rms value is applicable, and useful, for any electrical waveform, not just sine waves.

Andrew

So what should the formula mangled in Table 1 have been?

Ta,

Dave