Test Equipment Anonymous (TEA) : Discussion and Group Therapy Thread

[bd139]

As you get older everybody really should come to appreciate Cassandra's plight more acutely.

Doing most things for the first time is more interesting than repeating experiences. But by the 10th time...

Oh totally agree there!

[EC8010]

Doing most things for the first time is more interesting than repeating experiences. But by the 10th time...

When I was teaching, I found the third time I gave a given lecture was the best. By that time, I'd got the bugs out and useful details in. After that, it went downhill because it became routine.

[Zenith]

It rather depends on the job and how much you would like it to be turned into a routine action, involving no surprises. Something you can just do and be paid for.

For instance, fitting a kitchen. The first time you do it, there's all sorts of head scratching about how to go about it and there's ultra caution. You spend most of the time working out how to do it. If you had to do it a year later you'd do it in a third of the time. Then 15 years later, you've forgotten much of what you learned before and times have moved on. By then you may be earning so much it's easier to pay some daft bugger, who can't find a better way through life than fitting kitchens, to do it for you.

[bd139]

Couple of actual 10x8" prints from yesterday... (don't ask but it required eBay that puts TEA to shame )

IMG_3569.JPG

This is like crack

Been a few years but thoroughly enjoying it!

[AVGresponding]

As you get older everybody really should come to appreciate Cassandra's plight more acutely.

Doing most things for the first time is more interesting than repeating experiences. But by the 10th time...

Are you sulking?

https://www.eevblog.com/forum/chat/what ... msg6185271

[tggzzz]

Well, based on a quick test, here's a winner-winner-chicken-dinner story.

Idly browsing Gumtree (fleabay's zero cost local craig's list and farcebook marketplace killer alternative), and I spot a TTI dual PSU for £40. Picked it up on the way to Nottingham, and it turns out to be a AIM-TTI PL303QMD-P, i.e. 2* 30V 3A linear, with a few pleasant twists...

The current limit works correctly, i.e. no gross over voltages when you turn the PSU on[1].
True analogue V&I controls.
Series/parallel/tracking/independent.
"V-Span" function where you can limit the min and max voltage to, for example, 4.75V to 5.25V if you are using 74LSTTL
Can lock the controls.
Programmable over USB/ethernet/RS232.
Farnell price: £750+VAT

Only downside over my existing Tenma: missing a fixed 5V output that I use to power my Ikea gooseneck light. I'll survive

[1] I've recently tested a PSU set to 40mA 30V, with a 47ohm resistor so it should limit at ~2V. It output 30V for >100ms, then exponentially fell and undershot, and after a second got to the correct value!

[EC8010]

Those TTi supplies are very good ergonomically; I particularly like the way the current meter shows where you've set the current limit, then shows actual current when the output is switched on. What I don't know is their failure mode. Farnell supplies and earlier TTI supplies failed to maximum voltage, which is not good for anything connected... £40 plus fuel was a bargain.

[tggzzz]

Those TTi supplies are very good ergonomically; I particularly like the way the current meter shows where you've set the current limit, then shows actual current when the output is switched on. What I don't know is their failure mode. Farnell supplies and earlier TTI supplies failed to maximum voltage, which is not good for anything connected... £40 plus fuel was a bargain.

Based on a very quick play, I agree - and have already moved my Tenma PSU away from my bench.

I believe you can also see the set values while the output is on.

The manual indicates...
OVP and OCP Protection: (PL-P models only)
Measure-and-compare over-voltage and over-current protection are implemented in firmware and can be set via the remote interfaces only. Output trips off for OVP and OCP. Setting resolution: 10mV and 1mA. Response time: typically 500ms. For manual operation (Local mode) OVP and OCP are fixed at 105% of the instrument range maximum.

500ms and firmware seems like a poor substitute for The Real Thing.

[EC8010]

500ms is quite enough time for the magic smoke to escape...

According to Royal Mail, my Keithley 2010 is now less than five miles away.

It is now < 5m and gently warming before I apply power this evening. It hasn't got a handle. Why do people remove handles? There should be a special place reserved in Hell for the people who take the handles and bumpers off Keithleys and HPAKs. And it's not as if it has been rack-mounted; there's no rack-mount kit.

[AVGresponding]

I remove handles because I stack them up. I don't throw them away though

[Zenith]

It depends on the equipment. Sometimes it has a case and the handle is not accommodated in the case and so was never there or was discarded. Sometimes the handle is completely broken, or locks unreliably and so is a nuisance.

For most people the handle is a nice thing to have, but if it isn't there it certainly isn't a show stopper. It's like the front covers on scopes. I suppose to most people they were just bits of plastic that were never used and were often thrown away in the next general clean up.

[Robert]

Farnell and TTI were my favorite bench power supplies until I discovered Delta Electronica. They however are rare and even rarer as bargains unless bought faulty. A Delta SM7020D (700W 35V 20A / 70V 10A auto ranging) is now my main bench supply. Nice green LED displays and no fan. I do still have a few Farnell supplies from 30W to 1000W but the kW one is 4 four times the size of the Delta one and has a fan.

[EC8010]

I use the covers on all my 'scopes every time. I take care of my equipment and like it to stay as close as possible to as-new condition. After all, it was expensive, so why damage it? I never put fingers on screens because I don't like to see fingerprints/finger grease there. And once there, they can't be cleaned off without removing the anti-flare coating. My Tek TDS3032 oscilloscope is now 26 years old and the only thing that reveals its age is the floppy drive. I was traumatised when I clumsily touched one of its probe leads with soldering iron a few years ago. I look after my tools. Look after your tools and they'll look after you.

HPAK and Keithley handles fold neatly underneath the instrument; there's no need to remove them.

[Zenith]

Yes but in professional and industrial settings equipment isn't deliberately knocked about, but neither are people meticulous in looking after it. So handles can be broken and bits and pieces lost.

[EC8010]

I'll (reluctantly) agree with the above. Mind you, I looked after my kit at work exactly as I do at home; I had fought to get the money to buy the equipment on my bench, so I was certainly going to look after it. If you are known to look after your kit and extract real value from it it's a lot easier to persuade the bean counters to release the money... I often had people from other departments coming over and looking at my bench enviously, saying things like, "Wow, I don't have a bench like that!" To which I would respond, "Did you ask for it?" and the response would invariably be a mumbled "No". I didn't have to say, "Well, what do you expect, then?" But I did tell them that I had fought for every (usually quite expensive) item and justified it properly. Justifying kit properly means explaining the immediate need and also where it would be useful in the future. If you can't do both of those, you probably don't really need it.

[tggzzz]

500ms is quite enough time for the magic smoke to escape...

Yes indeed.

My test for current limiting behaviour is set 8V, 40mA and a 47ohm resistor as load. The voltage shouldn't exceed ~2V.

One PSU I recently tested only had a mains switch, not an output switch. It was, um, suboptimal. The voltage stayed at 8V for hundreds of milliseconds, "exponentially" decayed to below 2V, then exponentially rose to 2V. If I set 30V, then it reached 30V for a shorter time, but still took as long to reach the right value.

I ought to show pictures of the results.

[Zenith]

I'll (reluctantly) agree with the above. Mind you, I looked after my kit at work exactly as I do at home;

Then some of it will have been through the military, or worse, the education sector - technical colleges and universities. Sometimes the handles weren't all that robust anyway. All considered I find it remarkable that almost all of my gear has working handles, and most of it has the plastic caps which are there to finish it off.

The little feet at the back of Tek 400 series scopes are a source of irritation for me. They are always brittle and breaking up. Hitachi did much better feet. You can buy 3D printed ones on ebay at about £5 each. Too much for me. I'd be tempted for £5 a set of four.

[EC8010]

Then some of it will have been through the military, or worse, the education sector - technical colleges and universities.

Actually, I bought most of my equipment new. (Haggled on price, mind.) It's only since retiring that I've bought second-hand stuff. I'm learning that other people's idea of "looking after" kit is not the same as mine. My Hobbymat lathe is now 37 years old and mostly* in better condition than when it was new. It has been improved in many ways and I wouldn't like to go back to a stock Hobbymat.

Absolutely on education being the worst place for sourcing kit. Especially decade boxes. You can reckon on a few resistors being toast if they're ex-teaching. Come to think of it, some of the lecturers I knew were worse than the students.

My Bantam lathe came from a school and I'd like to get its metalwork teacher round the back of the bike sheds with a length of steel bar to explain to him just how displeased I am about the abuse it suffered at his hands. Fortunately, it wasn't used much, and the abuse has been repairable, whereas lots of use and wear isn't repairable (well, not at any reasonable cost).

* Mostly, because paint gets chipped on lathes.

[AVGresponding]

HPAK and Keithley handles fold neatly underneath the instrument; there's no need to remove them.

They stick out at the sides though, making it impossible to stack 1/2 width items side by side on top of full width ones.

[tggzzz]

500ms is quite enough time for the magic smoke to escape...

Yes indeed.

My test for current limiting behaviour is set 8V, 40mA and a 47ohm resistor as load. The voltage shouldn't exceed ~2V.

One PSU I recently tested only had a mains switch, not an output switch. It was, um, suboptimal. The voltage stayed at 8V for hundreds of milliseconds, "exponentially" decayed to below 2V, then exponentially rose to 2V. If I set 30V, then it reached 30V for a shorter time, but still took as long to reach the right value.

I ought to show pictures of the results.

Here's the awful PSU. Scale is 5V/div, 200ms/div. Turned on at 1 division, hits a peak 27V(!), hits a minimum 0V, finally reaches correct value (~2V) at the far right after 1400ms (1.4s!)

awful.jpg

[EC8010]

Here's the awful PSU. Scale is 5V/div, 200ms/div. Turned on at 1 division, hits a peak 27V(!), hits a minimum 0V, finally reaches correct value (~2V) at the far right after 1400ms (1.4s!)

I fear I'm going to have to check all my bench supplies. I'd already discovered a nasty Keithley 2400 sourcemeter switch-on overshoot in constant current mode when driving an LED string. The attachment shows the result later in the experiment, not the LED current itself. The very small DC with the cursor on it is what should have happened. The overshoot is 27 times the final current! Adding a 220nF capacitor across the load resulted in a nice exponential approach to final current. And I thought it was just a 2400 problem...

I've just waved a tape measure at meters with handles side by side and a full width rack-mount bit of kit. They're wider. I hadn't noticed that because my four full width bits of kit are stacked on top of one another. I have three stacks of half-width kit. And some other bits that are just plain non-rack-aligned.

[AVGresponding]

Here's what it looks like today. It will change when the Tenma load arrives.

current_stack.jpg

[EC8010]

OK, I can see why you have taken handles and bumpers off. My 6' bench isn't quite as crammed, but its shelf is stacked just as high.

[AVGresponding]

I did have it higher, but it was blocking the racking behind. I have a lot of things stacked in "storage" in my bedroom...

[tggzzz]

I did have it higher, but it was blocking the racking behind. I have a lot of things stacked in "storage" in my bedroom...

My daughter's bedroom has been repurposed Still not big enough