Floated scope: how to verify if no damage has been done?

[analias]

I get the concern here but with the many thousands of used analog scopes out there, many bought and sold repeatedly (via eBay and other venues), cycled through several users - surely many have been floated or subject to worse abuse.  Many are now sitting on shared benches, hacker spaces, schools, etc and used regularly by novices.  Is this really such danger once the obvious defects revealed by inspection and a trial burn in has been done?

That's a reasonable question.

The issues are related to

• "am I my brother's keeper" if I (or others) know there is something that might harm them. To put more of an emotional twist on it, replace "brother" with "child"
• "plausible deniability" in the event the worst happens

I don't have a neat answer to those, unfortunately.

Neither do I know what I would do if someone's knowing negligence killed one of my children. Sh1t happens and has to be accepted, but knowingly putting others at risk is different.

[analias]

This whole discussion seems a bit obsessive to me. Why are you so particularly concerned with the specific potential effect of the scope having been floated? In any scope with a 30 year history, who knows what kind of abuse, bad line voltage, or just degradation of critical components it may have suffered?

See my previous response.

If you encounter any scope that old in a multi-user environment, where you feel repsonsible for safety of all users (a classroom setting maybe?), wouldn't you have to decomission it?

Reasonable questions.

I'm not responsible, other than in the unsatisfactory "safety is everybody's responsibility" mantra - which isn't taken too seriously in that environment. Ownership is unclear.

It may be that decommissioning is the thing to do, but I would like to avoid that if possible. The floating probably hasn't done it any damage, but nobody has indicated the "floating" voltage so we simply don't know.

[Fungus]

I don't have a neat answer to those, unfortunately.

Neither does anybody here.

I think the "floating" thing is a red herring. Almost all the risk of a floating device is to the users, not the device.

Using this device is really no different to using any old, undocumented piece of test gear. If the chassis is grounded then there's almost zero risk of electric shock from it.

Children might poke wires through the holes in the case, yes, and an old CRO has higher voltages inside it than a modern DSO but that's nothing to do with it having been floated (or otherwise) in the past. I wouldn't place any real emphasis on that. This should be viewed for what it is - an old CRO. The biggest risk is from dried up capacitors and cobwebs inside it.

[Fungus]

...nobody has indicated the "floating" voltage so we simply don't know.

It may not have been floated for "high voltage".

A lot of people floated them simply to avoid accidentally shorting things with the ground clip while working.

[Simon]

Erm someone floated it and made it clear it was floating by labelling the socket. As such it could be dangerous to persons but there is no reason it is damaged.

[mtdoc]

I think the "floating" thing is a red herring. Almost all the risk of floating a device is to the operators, not the device.

Using this device is really no different to using any old, undocumented piece of test gear. If the chassis is grounded then there's almost zero risk of electric shock from it.

Children might poke wires through the holes in the case, yes, and an old CRO has higher voltages inside it than a modern DSO but that's nothing to do with it having been floated (or otherwise) in the past. I wouldn't place any real emphasis on that. This should be viewed for what it is - an old CRO. The biggest risk is from dried up capacitors and cobwebs inside it.

I agree. Visual inspection,check chassis grounding, then power it up and watch it for a while. If all is ok, then spend efforts on proper safety instructions for novice users and some relevant signage perhaps. That’s were the safety payoff is, not in worrying about theoretical but extremely unlikely events related to past use history.

[james_s]

I don't understand why people obsess over ridiculous specific hypothetical things like this. Floating the scope won't damage it, it's risky to do because the whole scope is live and you could get a shock while the scope is floating, not because it could damage the scope itself. This reminds me a bit about the thread where the guy was so paranoid about the possibility of a lithium ion battery catching fire that he was talking about incorporating a pyrotechnic ejection charge. It borders on mental illness.

[analias]

I don't understand why people obsess over ridiculous specific hypothetical things like this. Floating the scope won't damage it, it's risky to do because the whole scope is live and you could get a shock while the scope is floating, not because it could damage the scope itself.

I accept that you don't understand it. However, your assertion is false; see my reply #7 to your earlier assertion.

Do you have any response to the questions I posed at the end reply #7?

This reminds me a bit about the thread where the guy was so paranoid about the possibility of a lithium ion battery catching fire that he was talking about incorporating a pyrotechnic ejection charge. It borders on mental illness.

Such analogies generate more heat than light, and aren't worth discussing.

[analias]

Erm someone floated it and made it clear it was floating by labelling the socket. As such it could be dangerous to persons but there is no reason it is damaged.

The immediate risk is to anyone using a floating scope; there's no disagreement there (in this thread at least!).

However, I indicated in response #7 how the scope can suffer latent damage.

[analias]

I think the "floating" thing is a red herring. Almost all the risk of floating a device is to the operators, not the device.

Using this device is really no different to using any old, undocumented piece of test gear. If the chassis is grounded then there's almost zero risk of electric shock from it.

Children might poke wires through the holes in the case, yes, and an old CRO has higher voltages inside it than a modern DSO but that's nothing to do with it having been floated (or otherwise) in the past. I wouldn't place any real emphasis on that. This should be viewed for what it is - an old CRO. The biggest risk is from dried up capacitors and cobwebs inside it.

I agree. Visual inspection,check chassis grounding, then power it up and watch it for a while. If all is ok, then spend efforts on proper safety instructions for novice users and some relevant signage perhaps. That’s were the safety payoff is, not in worrying about theoretical but extremely unlikely events related to past use history.

Unfortunately there was signage, which was ignored.

Unfortunately currently instruction is patchy, and instructing novices is frowned upon - but this may be a stimulus to get that changed.

Neither instructions nor signs will help with people that think either it isn't dangerous or they know how to do it safely

Since resolution of those real and valid people-related issues cannot usefully be discussed here, I chose (and choose) to concentrate on a specific technical issue.

[tautech]

Better advice may come if you tell us the model #.

Probably not, since I'm after information about the damage that can be done to a generic scope. While this forum is better than many, there is a tendency to descend into minutiae and miss the big picture.

Having said that, it is probably relevant to mention that it is an SMPS PSU rather than a linear PSU, from the 24xxA series.

From that era floating scopes was a common occurrence by those that knew how and manufacturers allowed for this now frowned upon usage in their designs.

Perhaps for valve scopes, but I'm unconvinced that was true for 1980s SMPS/transistorised scopes.

Even in the 70s I knew that floating a scope was To Be Avoided.

Other than insulation tests on the SMPS transformer (removed of course) it's certainly a good question you ask.

Personally, if the scope operates correctly I'd reconnect the mains Gnd and just use it ......after a burn in for piece of minds sake.

Unfortunately it isn't just "personal".

It is a shared environment, and "ingenious fools" are present => it is difficult to make it foolproof.

Regrettably I think that Electro Detective's reply 86 in https://www.eevblog.com/forum/testgear/floating-scopes/ is the appropriate attitude, including ...
"I'm jumping ship (for once) and following the majority.. to recommend LEAVE WELL ALONE if not 100% sure,
or best practice is to dip into the piggy bank for a differential probe as front line measurement cannon fodder   
There are TOO MANY VARIABLES that are almost IMPOSSIBLE to document and break down here for the casual user wanting a 'fast fix'
which usually means a good chance for an earth/ground related BANG! "

Quite so, ED's reply is the 'modern' philosophy in today's litigation mad society where practices like floating scopes could never be taught for fear of culpability. It was by necessity back then as the vast bulk of scopes didn't have differential plugins nor were differential probes as widely available as they are now.
What I would offer as comment is a Tek 24** wasn't a cheap scope back then and any that would set it up as a dedicated floating scope would've known the risks to both themselves and instrument.
The likely extreme voltages it ever saw in floating mode would most likely be just rectified mains of which it could handle with comparative ease.
I get that if this scope is to be shared, culpability again rises it's ugly head where really any use of a scope and in fact any test gear exposes the operator to risk.

If this is too much to bear along with usage of a scope with uncertain history.....then buy a new scope !

[rstofer]

In the end, I think future failure modes are unknown and can't possibly be known.  How do I know my brand new scope won't self-destruct?  It's a Rigol, after all...  I have no idea what was done to my Tek 485 in the years before I bought it.  Floated?  Not floated? Over-ranged?  I don't know.  Nor do I care, I just plugged it in and have used it for the last 14 years.  Used it yesterday and it works fine!

If the risk is perceived to be high, junk the scope.  Personally, I would replace the cord to ensure that the chassis and BNC connectors are grounded and put it back in service.  I can't possibly predict some inter-winding anomaly and I doubt that I would worry so long as all exposed non-current carrying metallic surfaces were grounded.  Even if the scope went into hand grenade mode, I doubt the damage would be all that extensive.  A few pops, a few sizzles and that would be about it.

But in a group environment I wouldn't be so cavalier - I would let somebody else buy a different scope.  I wouldn't want to be involved with the purchase either.  Not my circus, not my monkeys!

[17_29bis]

I have been reading this topic and silently wondering how far this thoughtful investigation about possible damages because the ground was disconnected would go. I am trying to understand the magnitude of this problem and somehow all what I see or can explain as a former el. engineer is that it is mostly a liability related issue (versus common sense) than anything else.

Just think for a second - in recent past many countries (like Soviet Union for example) did not have 3 pole plugs at all and it did not prevent them from creating, debugging, manufacturing, using different electronic devices to allow people to go to space or to the bottom of the ocean. I don't want to switch the topic and start a discussion whether or not my example covers all bases, but I think you got my point.

And when I think about liability issues in North America (let me be politically correct, since not all countries in North America are the same) I think that cases like Liebeck v. McDonald's Restaurants, when a 79-year-old woman who suffered third-degree burns in her pelvic region when she accidentally spilled hot coffee in her lap after purchasing it from a McDonald's restaurant was awarded $640,000 ( at first the amount was 2.8 million but later was reduced to  $640,000). And this list is huge. And it even includes some urban legends like "Winnebago driver case" when the driver set the cruise control at 70 and went into the back to make coffee and later sued Winnebago for not advising him in the owner's manual that he couldn't actually do this ;-(
 
So is it really a technical problem being discussed here or something else?

PS: edited 10 minutes later - even my MacBook pro has two adapters - 2 and 3 pronged plugs  (N.A. style)  And whatever you connect through USB (a scope, a logic analyzer etc ) to your laptop will be floating too in case of 2 pronged plug. What is a big deal here?

[analias]

Regrettably I think that Electro Detective's reply 86 in https://www.eevblog.com/forum/testgear/floating-scopes/ is the appropriate attitude, including ...
"I'm jumping ship (for once) and following the majority.. to recommend LEAVE WELL ALONE if not 100% sure,
or best practice is to dip into the piggy bank for a differential probe as front line measurement cannon fodder   
There are TOO MANY VARIABLES that are almost IMPOSSIBLE to document and break down here for the casual user wanting a 'fast fix'
which usually means a good chance for an earth/ground related BANG! "

Quite so, ED's reply is the 'modern' philosophy in today's litigation mad society where practices like floating scopes could never be taught for fear of culpability. It was by necessity back then as the vast bulk of scopes didn't have differential plugins nor were differential probes as widely available as they are now.

Ach. I don't think ED's statement supports the contention that the fear of culpability is a central issue. His "conversion" seems to be based on a realisation of the reality that there are subtle dangers that cannot be quickly and easily taught to newbies.

That floating was done in the past is, as you say, because the equipment wasn't (widely) available.

What I would offer as comment is a Tek 24** wasn't a cheap scope back then and any that would set it up as a dedicated floating scope would've known the risks to both themselves and instrument.

ISTR an anecdote on TekScopes about someone that realised it was dangerous, took precautions - and still died.

The likely extreme voltages it ever saw in floating mode would most likely be just rectified mains of which it could handle with comparative ease.

That could add 350V (240*sqrt(2)) across some components.

I get that if this scope is to be shared, culpability again rises it's ugly head where really any use of a scope and in fact any test gear exposes the operator to risk.

If this is too much to bear along with usage of a scope with uncertain history.....then buy a new scope !

The "it might hurt someone else" is the key consideration, as opposed to the Darwin Award.

If someone is prepared to float an old scope, there's nothing preventing them floating a new scope - but that's outside the scope of this thread.

Ways of increasing confidence in lack-of-danger is the topic of this thread.

[analias]

In the end, I think future failure modes are unknown and can't possibly be known. ...

If the risk is perceived to be high, junk the scope.  Personally, I would replace the cord to ensure that the chassis and BNC connectors are grounded and put it back in service.  I can't possibly predict some inter-winding anomaly and I doubt that I would worry so long as all exposed non-current carrying metallic surfaces were grounded.  Even if the scope went into hand grenade mode, I doubt the damage would be all that extensive.  A few pops, a few sizzles and that would be about it.

Those were my initial thoughts, until I did some research and came across the Tek statement. That raised doubts that my inaction might result in a newbie being hurt.

But in a group environment I wouldn't be so cavalier - I would let somebody else buy a different scope.  I wouldn't want to be involved with the purchase either.  Not my circus, not my monkeys!

Quite; that's part of the dilemma

[analias]

I have been reading this topic and silently wondering how far this thoughtful investigation about possible damages because the ground was disconnected would go. I am trying to understand the magnitude of this problem and somehow all what I see or can explain as a former el. engineer is that it is mostly a liability related issue (versus common sense) than anything else.
...
So is it really a technical problem being discussed here or something else?

I've tried to frame it as a technical problem which can, hopefully, be resolved technically.

There are indeed non-technical issues that also need to be addressed. The technical issue may be a good way to force other people to deal with the non-technical issues - but that's a different argument.

[tautech]

Regrettably I think that Electro Detective's reply 86 in https://www.eevblog.com/forum/testgear/floating-scopes/ is the appropriate attitude, including ...
"I'm jumping ship (for once) and following the majority.. to recommend LEAVE WELL ALONE if not 100% sure,
or best practice is to dip into the piggy bank for a differential probe as front line measurement cannon fodder   
There are TOO MANY VARIABLES that are almost IMPOSSIBLE to document and break down here for the casual user wanting a 'fast fix'
which usually means a good chance for an earth/ground related BANG! "

Quite so, ED's reply is the 'modern' philosophy in today's litigation mad society where practices like floating scopes could never be taught for fear of culpability. It was by necessity back then as the vast bulk of scopes didn't have differential plugins nor were differential probes as widely available as they are now.

Ach. I don't think ED's statement supports the contention that the fear of culpability is a central issue. His "conversion" seems to be based on a realisation of the reality that there are subtle dangers that cannot be quickly and easily taught to newbies.

That floating was done in the past is, as you say, because the equipment wasn't (widely) available.

Yes but if any of us on the forum suggest floating scopes, aren't we in some way culpable ?
The dangers aren't subtle, they're deadly !

What I would offer as comment is a Tek 24** wasn't a cheap scope back then and any that would set it up as a dedicated floating scope would've known the risks to both themselves and instrument.

ISTR an anecdote on TekScopes about someone that realised it was dangerous, took precautions - and still died.

As per above and user error cannot be overlooked.
Drive a car at highway speeds on back roads without a seatbelt and the result can be similar.

The likely extreme voltages it ever saw in floating mode would most likely be just rectified mains of which it could handle with comparative ease.

That could add 350V (240*sqrt(2)) across some components.

Exactly but it's an offset that the whole scope is subjected to not so much a stress on individual componentry across the whole scope. The PSU is where the greatest stress will be.

I get that if this scope is to be shared, culpability again rises it's ugly head where really any use of a scope and in fact any test gear exposes the operator to risk.

If this is too much to bear along with usage of a scope with uncertain history.....then buy a new scope !

The "it might hurt someone else" is the key consideration, as opposed to the Darwin Award.

If someone is prepared to float an old scope, there's nothing preventing them floating a new scope - but that's outside the scope of this thread.

Ways of increasing confidence in lack-of-danger is the topic of this thread.

The safest move is to restore the mains Gnd, period. That assumes the supply ground is sound and in perfect order.

In the end, I think future failure modes are unknown and can't possibly be known. ...

If the risk is perceived to be high, junk the scope.  Personally, I would replace the cord to ensure that the chassis and BNC connectors are grounded and put it back in service.  I can't possibly predict some inter-winding anomaly and I doubt that I would worry so long as all exposed non-current carrying metallic surfaces were grounded.  Even if the scope went into hand grenade mode, I doubt the damage would be all that extensive.  A few pops, a few sizzles and that would be about it.

Those were my initial thoughts, until I did some research and came across the Tek statement. That raised doubts that my inaction might result in a newbie being hurt.

And actually how old is that Tek statement ?
You can be quite sure their documentation has been updated to make users fully aware of the risks of floating scopes so not to expose themselves to today's litigation mad world.
Many Tek documents that were once on their website are now gone without trace unless you can find them stashed on another website.

[mtdoc]

I've tried to frame it as a technical problem which can, hopefully, be resolved

There is no technical resolution. As stated, there are basic checks that can be done on any old piece of test equipment. Beyond that, common sense measures like GFCI outlets and basic safety rules is all you can do.  If that doesn’t satisfy your safety and  litigation fears, then removing yourself from the environment (or position of responsibility) is likely the only way to resolve your concerns.

[EEVblog]

MODERATOR: User analias has been banned for operating multiple accounts.

[james_s]

I just now noticed what the OP's username is. I wonder why?