Secret Scotland

If it's secret, and in Scotland…

LNT – Strange case of the wonky DC current clamp adapter

I was caught out by a slightly unexpected problem after I threw together a small adapter intended to make DC current measurement a little easier.

I recently took possession of a clever new device, a DC current clamp meter which allows DC current to be measured with the same ease as AC current, using a clip, or clamp, which is placed around one of the current carrying conductors, and avoids the need to break into the circuit and insert an ammeter

In the past, this only worked with AC current as it depended on transformer action, with the conductor forming the primary, and a winding on the current clamp forming the secondary.

Now, magnetic (Hall Effect) sensors are used to pick up the steady magnetic field around a conductor carrying DC current, bringing the same non-invasive technique to this measurement.

I’ve been using this device for a while now, and was quickly impressed at how DC currents down to a few mA could be measured accurately, and matched simultaneous measurement made using a conventional meter in series with the same circuit under test.

One important thing to remember is that such meters have to be zeroed before taking a reading, The Earth’s magnetic field is detected by the sensor, causing a reading, and the orientation of the sensor in that field will also cause a reading. So, if the meter (sensor) is moved, it should be zeroed before taking a reading.

I also found it has a major advantage in that it does not load the circuit by adding a series resistor. In a normal multimeter, the current usually passes through a series resistor to develop a voltage which the meter shows as a current. Unfortunately, at low currents, this resistor has to be large enough to produce a volt drop across itself which the meter can display. This can alter the current significantly, and experienced techs will take this into account. As a real life example, in a battery operated set of 34 white LEDs, these showed about 40 mA with the clamp, but this figure dropped to about 20 mA when an ordinary multimeter was used (in series with the battery and LEDs), and they became significantly dimmer due to the increased load and reduced current. Inserting the conventional meter was therefore causing a significant error.

As it proved to be so good for low currents, I wanted to use it for battery powered devices, but these often hide the batteries inside a battery compartment, so have no leads the meter can be clipped around, or have a single moulded lead containing both conductors

I threw together the item shown below, where the loop of wire on the right is soldered to either side of a very thin (<0.25 mm) piece of double-sided fibreglass PCB material which can be pushed/placed between one of the battery terminals and its connector in a battery compartment.

DC current clamp adapter

DC current clamp adapter

I should have known better…

That things wouldn’t be that easy.

I’d carried out a number of tests to satisfy myself that there wasn’t any significant effect due to having the clamp near the other conductor (carrying the ‘return’ current in the opposite direction to the conductor which was clamped), of the direction of the current (relative to the clamp), and (within reason) how carefully, or not, the conductor passed through the clamp

The prototype adapter shown above apparently DOES produce anomalous readings.

I found that reversing the direction of the wire through the clamp, or just moving the wire, could cause a significant difference in reading. The reading in one direction would fall while that in the other direction rose. Very roughly, if the current was 40 mA, then I could find that the reading in one direction might rise to 60 mA (as I moved the wire), while it would fall to 20 mA if I reversed the direction of the wire through the clamp. I had suspected a possible variation (when I noted the unintended  small loop the prototype formed), hence the check – which proved to be worthwhile.

Rather than agonise over the ‘Why?’, I just cut the blue wire and extended it, to avoid having such a pronounced loop, ensuring the wire can be kept straighter as it passes through the clamp.

A quick check confirmed that the directional anomaly appeared to have been cured by this fix.

I suspect  combination of effects – the position of the sensor in the magnetic circuit within the clamp, and the shape of the magnetic field around that unintended small loop, which will produce an asymmetric magnetic field around the clamp. These two effects could result in reading that change depending on where that little loop lies around the clamp. This doesn’t happen when the conductor passes straight through the clamp, and produce a reasonably symmetric field around itself.

Oh well…

The real test had actually just been to see if that little piece of double-sided PCB would slide into the battery compartment – which it does perfectly.

Finding the anomalous readings was a bonus, which I can correct for when I make a tidier version of the adapter.

Historically this is nothing new

While i was poking around the archives, I was reminded that DC clip-on ammeters are nothing new, as seen by the wording on this Tong-test scale.

Note the correction figure shown at bottom left, and the patent date on the right, 1924.

AC DC Tong-test scale

AC DC Tong-test scale

These used to be popular for measuring DC current of rechargeable cells in factories – not much chance of measure 20 mA with them though.

This type used moving iron meter movements, which relied on the magnetic field produced in soft iron by the current, and could operate on AC or DC circuits.

They also achieved multi range operation by swapping out the entire movement, complete with scale, and you can see the clips on the side of the instrument, which held each movement in place within the magnetic circuit of the clamp behind. The moving iron part (at the base of the pointer) slid into a hole in the centre of the clamp.

AC DC Tong-test view

AC DC Tong-test view

Not exactly a handy pocket meter – they came in a carrying case, holding the clamp plus a selection of scales.

And finally – SAFETY!

I have to be honest, and admit I wasn’t wearing the proper safety gear when I carried out the tests mentioned above 😦

No hard hat…

Or full face visor.

Or safety glasses under the visor.

Or full face mask.

Or overalls.

Or high voltage rubber gloves.

Or gloves to protect those gloves (from piercing).

Or, out of sight, insulated footwear.

Or a rubber mat.

Using a clampmeter safely

Using a clamp meter safely

It’s not a bad idea (I’m having fun, not mocking).

I used to have a 1 cm length of wire embedded in the clear plastic face of one of my multimeters, blown there and melted into place as it cooled from white-hot to red, after a fault developed in ordinary mains as I was carrying out some tests. I left it there for years, and only removed it recently as it became too irritating where it blocked visibility of the scale.

When I was called in to carry out tests in a factory, I was intrigued when the sparky there had everyone stand behind a brick wall each time we powered up a suspect control panel. It made a lot of noise, but never blew up. Having seen such an event in videos, I know I don’t want to be standing beside such an event. Safety gear wouldn’t really do a lot of good where industrial power is concerned and there’s a serious failure.

14/09/2019 Posted by | Civilian, photography, Uncategorized | , | Leave a comment

I went to Yorkhill – and all I got was signs

Yesterday was (almost) interesting after I had to go to Finnieston in the early evening.

Rather than just head straight back home once my business was done, I took a chance as thunder boomed around (with no lightning, or rain) and decided to walk through Yorkhill (the part behind Kelvin Hall at least) and on to Partick, since I’d sped through the streets in the past, but never on foot.

Sad to say, as regards the part I walked through, there didn’t seem to be any ‘Points of Interest’. The buildings/tenements all seem to be fairly plain, and I didn’t see any decorative features or architectural variations.

Notably, the area was home to the Royal Hospital for Sick Children, referred to locally as “Yorkhill” or “Sick Kids” when it was in operation.

Today, as of 2015, the facility has become The West Glasgow Ambulatory Care Hospital, a healthcare facility created to house the remaining outpatient service’s and the minor injury unit of the Western Infirmary (replaced by a large hospital campus elsewhere). This lay nearby, but was closed a few years ago, and has now been razed, as noted in my ‘concrete block’ posts.

A classic entrance sign still exists on the approach road to the old hospital.

While I understand those who object to such artefacts being removed, I’m also more of a realist than the idealists.

This sign SHOULD be removed and preserved in one of Glasgow’s museums.

Instead, I suspect it will just gradually decay where it is, be vandalised by some morons one day, or maybe even be stolen and sold by a rogue ‘salvager’ for a profit. However, I doubt it could be removed like that, and the sign;s construction means the whole stone post it is attached to would have to be taken, or a very careful removal and reconstruction carried out.

Yorkhill Sick Children Hospital Sign

Yorkhill Sick Children Hospital Sign

On a lighter note, there was a more modern sign seen just along the road.

Yorkhill To Let Toilet Sign

Yorkhill To Let Toilet Sign

01/08/2019 Posted by | Uncategorized | , , , | Leave a comment

Lion and Unicorn on historic Glasgow University staircase smartened up for 330th

With a year in hand before the actual 330th anniversary, I wasn’t in a hurry to go get new pics of the Lion and Unicorn in Glasgow University.

I had collected some pics fairly recently, and you can find some more detail of their history in that post. No need to repeat here.

However, the historic pair are, it seems, set to celebrate their 330th birthdays next year, and the gold paint has already be drawn from stores in preparation for the event.

So, since I was nearby, AND has some unexpected spare time in hand, I just had to make the effort and walk up the hill to the university.

Lion and Unicorn Retouched

Lion and Unicorn Retouched

It’s a bit unfortunate that you can’t really get a good angle/view of the pair from the front, as they sit part way up the staircase.

The views are all from just below, or just behind and to the side.

For what it’s worth, my colours are accurate and realistic, unlike some other pics seen online, where they seem to have been made more vivid.

29/07/2019 Posted by | Uncategorized | , | Leave a comment

Don’t miss Lil BUB’s 8th birthday

Still on the theme of “Things only happen when I’m away”, I see LiL BUB turned 8 recently, and had a party.

I don’t see much of the ‘Internet cats’ these days, as the original sites that tended to focus on them have gone downhill, and I just don’t visit, so almost missed this too.

And I’m still a bit down over the loss of Grumpy. Did you realise both were girls?

But this is about smiling, and just look at the faceplant as soon as BUB get near the cake, even before it’s ready.

Couldn’t be there, but let’s not forget the sight of them together.

04/07/2019 Posted by | Civilian, Uncategorized | , , , , | Leave a comment

Cat with sound effects

Sound on, smile on…

19/06/2019 Posted by | Uncategorized | , | Leave a comment

Today is Chocolate Ice Cream Day

07 June is Chocolate Ice Cream Day.

Since I got carried away with the post about VCR Day (which also falls on 07 June), I’ll keep this short.

Chocolate Ice Cream…

No explanation needed – go eat some!

For what it’s worth, my preference is for the streaky type – I find the taste is less overwhelming than the uniform option.

While it may be hard to believe you can have TOO MUCH chocolatiness, you can, and if it’s too strong it limits the amount of chocolate ice cream you can eat.

And that’s… not a good thing.

Chocolate Ice Cream

Chocolate Ice Cream

07/06/2019 Posted by | Uncategorized | | Leave a comment

There goes Dippy (and Leonardo)

Just quickly, an automatically created panorama of Dippy’s last hour (at 16:00) in Kelvingrove.

I don’t usually use this as the result is ‘mushy’ at best (and it’s quite dark in Kelvingrove), but since I have plenty of decent pics, why not?

Click for bigger.

Dippy end pano

Dippy end pano

The Leonardo da Vinci sketch exhibition also ended today.

As there are plenty of pics of the sketches (and that room was REALLY dark to prevent light damage to the originals), here’s the crowd one hour from the absolute end of this one too.

Leonardo end pic

Leonardo end pic

06/05/2019 Posted by | Uncategorized | Leave a comment

Oh-oh… Looks like my unhappy opinion of the NPA might not be the only one

I’ve said before that I’ve long given up on passing comment on the NPAs (National Park Authorities), especially since I lost the option of being a regular visitor to the Loch Lomond area some time ago.

So now you know I think they’re (around Loch Lomond at least) useless,

I spotted news of a proposed major development at Loch Lomond, and it seems to pretty much fall into line with the negative things I think about NPAs.

This sounds kind of what like I was saying years ago, and the NPA still seems to be letting developments be added.

So much for preserving the place, unspoilt.

More than 50,000 objections have been lodged against a new £30m tourist development at Loch Lomond.

The proposals include a 60-bedroom apart-hotel, 32-bedroom budget accommodation, a craft brewery, holiday homes, leisure centre and restaurants.

But the Lomond Banks development at Balloch has proven controversial with strong local opposition.

Campaigners fear the project will spoil the scenery and limit access to the shoreline for locals.

Alannah Maurer, of the Save Loch Lomond campaign, told BBC Scotland’s The Nine: “A national park is a theme park in its own right, a natural theme park and in this time of climate change we should be looking at conserving that natural theme park.

“Those buildings will dominate the scenery, they will dominate the village of Balloch.”

Anger over £30m hotel and leisure complex for Loch Lomond

They (the developers, and the objectors) can’t both be right, so this will an interesting confrontation between two fairly outspoken groups who would seem to be unlikely ever to agree.

Benidorm pic still seems appropriate, so…



04/05/2019 Posted by | Uncategorized | , , | Leave a comment

Look at that smile

I sometime go for a quick wander while listening to the organ recitals at Kelvingrove, mainly to get a better view of the video displays relaying the performer’s feet and hands, particularly the pedal board, which can be interesting to watch.

I’d been standing beside a couple of tourists (why are they the quiet ones?) before changing sides on the balcony, and happened to look across at where I had been standing.

What a nice change from the usual babbling, sometime arguing, disinterested locals and their noisy brats who usually ruin whole sections of the recital, especially at the moment with the schools on holiday.

It’s almost a pity that the lights in the central hall have been switched off this week, as the Sun shines in, which makes the place a little darker than usual, and the poor old camera couldn’t quite cope with the marginal conditions.

Kelvingrove Smile

Kelvingrove Recital Smile

I probably smiled as much when I saw this video clip of a cat sleeping in a piano.

While it would be nice to have a Kelvingrove organ cat, I doubt even the cat would sleep through a performance if it was on the keyboard.

While the lowest notes don’t cause vibrations in the central hall, having been to a demo in the organ balcony, I now know the lowest notes are powerful enough to make the stone floor underfoot vibrate up there (well, the organ pipe do sit just behind the console).

24/04/2019 Posted by | Uncategorized | , | Leave a comment

Mural surprise along a lane

With so many murals now being listed almost ‘officially’ on some web sites and publications, it’s almost something of a surprise to go wandering down lanes and finding examples not seen listed in those sources – or I’ve just missed them.

This one turned up in Burgh Lane, Hillhead, not far off Byres Road, and is on the wall of the Western Baths, which is just as well, as it features – the Western Baths!

Quite a place by all accounts, I managed to miss my chance to get in for a look at the place before it was revamped and became a club, although much has been retained.

Prior to the changes (and I have to say I am going by memory here, risky), I think the place, exclusive as it was, was under threat of being lost, but that seems to be a thing of the past for it now. It seems to be doing well.

The Western Baths Club is a Victorian era private swimming and leisure club founded in 1876. The club remains at its original site at 12 Cranworth Street, Hillhead, Glasgow. The 19th-century baths are protected as a category A listed building. Along with the Arlington Baths it is the one of two clubs of its kind left in Glasgow.

I had to go back a couple of times – I didn’t feel like taking an awkward pic (ie not a quick snap) with a small crowd of ‘yoofs’ who were intent on studying the contents of plastic bags they were carrying, standing on almost the same spot I had to be on to take the pic.

The lane is fairly narrow, and the mural fairly wide – there’s no chance of catching with any ordinary wide lens.

I had to stitch four shots together to get the whole thing in one pic.

It actually worked.

Click for bigger.

Burgh Lane Western Baths Mural

Burgh Lane Western Baths Mural

Although I don’t have any accurate tools to correct the distortion in such a wide stitch, I thought I’d try anyway, just to see how it did.

It does help, but if you look at the extreme edges on the left and right of the second image, you can see how this correction tool is adding more (different) distortion as it corrects the original distortion.

Click for bigger.

Western Baths Mural Version 2

Western Baths Mural Version 2

26/03/2019 Posted by | Uncategorized | , | Leave a comment

Today is No Smoking Day

13 March 2019 is No smoking Day.

Unfortunately, another wandering day that falls on a different date most years – set as being the second Wednesday of March.

It may be an addiction, but that’s no excuse for starting!

Why is it so important to have a day set aside for this? Over the last few decades, it has become very clear just how extremely dangerous smoking is. There are toxins in smoke that cause many different forms of cancer from the mouth to the lungs. What is also important to know is that while it may be a personal choice to smoke or not, when one smokes near another person -or even a pet – the second-hand smoke is just as dangerous to them. So, it really isn’t just a personal decision. The protection of people who do not want to be affected by second-hand smoke has led to new laws in most communities that ban smoking in most public spaces.

Sadly, the many myths, beliefs, and excuses for smoking are STILL deep set in our various cultures, reinforced by the lies fostered by the tobacco companies in order to suppress the truth and keep people addicted.

This was especially important to those companies then (as it still is today, and they move into less well-informed countries and communities, as they knew full well that the more they got their customers to smoke, the sooner they killed them, and needed replacements to take their place, and keep up sales and profits.

Previous no smoking day

See also the fun here:

Anybody else miss those old educational cigarette adverts

Smoking Birth Weight

13/03/2019 Posted by | Uncategorized | | Leave a comment

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