Gallery, Projects and General > The Design Shop
Microwave owen transformer spot welder?
awemawson:
To think that for years and years I carried a Textronix 465 in the car as a standard computer servicing tool that had the mains earth lead disconnected and poking out of the plug so that it was obvious to all.
But Health and Safety hadn't been invented then, nor had RCDs so it was OK :lol:
But on the other hand Common Sense hadn't been banned then, so that probably saved us :ddb:
PekkaNF:
Yesh...that was all normal when I was a student and lab tehnicias hovering among us to prevent us from sme of the most dangerous stuff.
My problem here was a senior moment....I'm aware of the problem and in order to avoid it I had all figured and checked out, but then I put the plug wrong way in.... I actually have two poplarized Shucko plugs, but no power strip that is polarized.
We used flot sopes, but the scope had long plastic extensions for the knobs...for the reason mentioned before. We were wondering why the front panel was metal and plastic knobs had metal parts....maybe it's just cruelty to apprendices?
I had a look on current probes and isolated probes....good thing that I was sitting down. I must have sunk deeper in the couch. Least it felt that way.
Is there any economical floating probe/isolation amplifiers available for a) mains measuremet b) instrument level signals 24vdc, +/- 10V?
Or am I better of cobbling on a plastic enclosure double insulated system, that has it's own isolated PSU, then DIY voltage divider/differential amplifier and a EL-cheapo digital scope with very limited bandwidth but cheap price tag? Sort of bangood scope mentioned here?
Pekka
PK:
Re all of the above, if you slow down and think it through then the risk is zero. The cautionary language is for the young'uns reading this who aren't going to take that approach.
On the topic of isolation..
We have a few DIY isolation transformer boxes here at work that are nothing more than two mains to 24 transformers wired back to back. We're still alive.
It sounds a bit excessive, but the cheapest option for you might be to get two more oven transformers and wire them together. This will give you an isolation transformer of some significant capacity...
I'm not sure I understand the requirement to isolate both the scope supply and the signal of interest?
Re options:
A battery powered handheld scope isn't the same thing as an isolated scope (look for cat II or cat III specs). Sadly the manufacturers of these devices understand this and charge commensurately.
All handheld scopes are complete crap compared to the same dollars in a bench scope, mostly because they have tiny, low res screens, also mostly because they have tiny capture buffers and finally mostly because they have slow processors which makes the menus slow to pop up and hard to use.
So my vote is for the bench scope and isolation....
awemawson:
There are some excellent bargains on eBay for analogue Tektronix oscilloscopes. £200 buys you a professional instrument in good order complete with probes - just because everyone wants more recent digital 'scopes it doesn't mean the analogue ones no longer did what the always did !
My 465 may not get used every day (or even every month!) but I certainly wouldn't part with it.
PekkaNF:
OK. ordered one hal conraption that might get me somewhere on current measurements, this type, but different shop:
http://www.amazon.com/Hantek%C2%AE-Current-Clamp-kHz-20mA/dp/B00BLD6FB8
It's on the mail...I have palyed with hal clamps and transducers before...not having utmost trust on that one, but it IS isolated!
More questions:
1) Anyone found source for reliable shunt resistors (kelvin type)? No point of buying bad one measuremet, this one will be used for accurate measuremets and verify other measuremets.
2) Found few reasonable circuits for isolated differential probe, one way too much overspeck, but not too expensive BUT circuitboard would be a problem.
Here board and expense is no problem, but I have no idea of performance/speck.
http://www.chip45.com/products/detail.php?pid=isoprobe-1-kit
**UPDATE:
Looks like AM1200 isolation amplifier has Small Signal Bandwidth 100 kHz:
http://www.ti.com/product/amc1200
maybe 50% of it is final total system bandwidth??? Looks like a one of these cheap oscilloscope kits (with isolated power supply) would offer all that (except reference to another channel):
http://madmodder.net/index.php/topic,11145.0.html
**
Could not find circuit diagram or spesification. I would be very fine pretty much buying or soldering, but small surface mounted componenets or making PCB...
baby steps
Pekka
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