Mechanical Resonance (Projects)

[picowatt]

Guys,

Did you read what he posted.  He has both scopes isolated from mains ground and both scopes isolated from each other.  He will NOT be creating a short from one side of the AC to the other side of the AC.

Of the list of bad things that can happen, a dead short, spark, a blown circuit breaker and a brief WTF moment followed by the subsequent discovery of damage to equipment is the best case scenario.

The only real danger will be if he touches both scope cases at the same time as most scopes do have the ground side of the probe tied to the case of the scope.

That's exactly right, there is a very real danger to life and limb.

If you have been following his posts, you would be aware of what he is wanting to do and his limited understanding of  how and why the AC line is wired as it is.  Having one of the scopes, its inverter, and its battery at line potential in close proximity to another scope, inverter, and battery at the neutral or opposing line potential is just asking for trouble. 

One look at the posted photo of his bench setup should be cause for extreme concern...

PW

[wattsup]

@PW and all

Still at work but will be home tonight.

My scopes are both floating since each one is driven by it's own car battery and its own inverter so there is no danger in blowing the equipment. 

The reason I am going straight to mains with these floating probes is to remove any possible excuses of using a Variac or any step-down transformer as being a hindrance from actually using the real neutral line. I fully understand the danger but have done some quick tests last night and there is no adverse effects. As long as you do not touch two terminals with your hands and this is why I am employing SM's one hand technique. The probe and ground can now go on either the hot or neutral without any problems.

I also have a direct ground line that I had put in the backyard a few years ago which is a 1/2" by 8' long solid copper rod that I planted vertically 10' deep so the top is 2 feet below the surface. I have a copper line going from there to my bench to also test the differences between the mains neutral and a true Earth ground. I already saw something that I will video as curious and am sure will have some of you scratching your heads to explain it. I don't have an answer as of yet.

I do not suggest anyone do this because yes, there is an element of danger but I am perfectly confident of my handling skills otherwise I would not do it. I know my limits and also know when to ask questions that others may be more experienced to answer, hence my question about how the scope derives the differential sine wave with a probe and ground. I need an official EE explanation as this will be part of my overall analysis later on. The only other variable is the added task of making a video which will require some additional attention that must not detract me from the proper handling. But I think I will be OK.

Thanks for the concern. I will be back soon but on the JT thread so it will again become useful and free this one for mechanical resonance works which is again a real treat for the mind.

wattsup

[wattsup]

@PW

Just saw your post and thanks. I will add a thick piece of wood between the two scopes event though the top one is plastic with plastic feet but just in case. I will also wear some gloves and make a point of not touching the lower scope chassis. hahahahahahahaha

wattsup

[citfta]

Hi wattsup,

I don't see where anyone answered your questions about a scope.  I am not an EE but I have used scopes for over 40 years and even from time to time had to repair one.  If I understand your question correctly you want to know how a scope displays the signal on the screen.  The old analogue scopes are the easiest to understand so we will start with them.   As you are already aware the ground clip of your probe is connected to the chassis and ground side of the amplifying circuit.  This just becomes a reference point to use as a convenient place to compare the signal to.  With your scope floating as you have done this reference point is entirely relative to everything else.  This allows you to make measurements that are NOT referenced to ground.

In simple terms if we wanted to measure the voltage on a 12 volt battery with a scope if we connect the ground clip to the negative post we would see 12 volts positive when the signal side of the probe was connected to the positive post.  If we connect the ground clip to the positive post then we would see a negative 12 volts on the signal side.  Whatever we see on the signal side is in relation to where the ground clip is connected.

I am not sure how much further you need information but we will go a little farther.  The signal on the probe is fed to an amplifier that the sends the signal on to the deflection plates of the crt to cause the trace to move up and down according to the signal on the probe.
A digital scope doesn't actually display the signal directly like the analogue scope.  Instead it takes very tiny very short samples of the signal and then plots the curve on the screen.  These short samples allow the math functions to have something to calculate.

The simplest way to think of a scope is that it is just a voltmeter with a visual display so you can see changing voltages and complex waveforms.

If I haven't answered you questions please explain again what it is you are trying to understand.

Take care,
Carroll

[Magluvin]

Hey Watts

Is there resonance in your experiment? If so, you can make another thread on this board on that? Just that this thread is working with mechanical resonance. Dont want to thicken it up with other things.

If it is on this board, it will be moderated at your request if needed. Just ask Brad or me if there are any problems.

Mags