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Oscilloscope and AC home line noises

wrinke

Feb 25, 2023
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Hi everyone,
I have question about my new oscilloscope and noises on my home electrical system.

I have purchased a very economic oscilloscope (HANMATEK DOS1102), seems works fine. But after I was surprise to see noise on oscilloscope signal when I switch on and off room light. That was very strange because the system that I was analyzing was a battery system. So I simplify the circuit max as possibile, I just connect the probe between AA battery poles, I switch again the light on and off (the light is controlled by step relay) and the noise appear again.

Is it possible that the oscilloscope have not any kind of noise filter on its power supply?!?

is it a normal behaviour?

tnx for help,
Marco
 

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wrinke

Feb 25, 2023
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It Is just battery AA, I put the ground of prove to - of battery, head of probe is hooked to + of battery. The relay Is hager epn520. In this scenario I have that signal, otherwise, if I just connect probe ground with its head, the signal became line on zero level, as expected, but became immune from relay noise.... I cannot figure why.....
 

Bluejets

Oct 5, 2014
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Is it possible that the oscilloscope have not any kind of noise filter on its power supply?!?
Plenty of introductory tutorials on the internet on "how to use oscilloscope" and it looks like a good time for you to get started and do some study on how things work.
More than likely some good reading material out there as well.
Best place to start........
 

Delta Prime

Jul 29, 2020
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The scope probe is like a little dipole antenna, so you're looking at near field E coupling here - basically just capacitive.
(mutual inductance in the case of the H field and capacitive coupling in the case of the E field).
The scope probe plus the scope input channel have a high-impedance (typically 10 MΩ for a 10X and 1MΩ for a 1X).
Scope probes will pick up Fluorescent Lighting, Motors with brush commutators, household switches can and do bounce in the RF spectrum along with 50 and 60 hertz hum AM, FM. So on and so forth. Especially from cheap probes (just kidding).
 

Delta Prime

Jul 29, 2020
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Pretty close to the truth so why "just kidding"..
Because if it was me I would be very proud of my new scope and probes.
Pretty close to the truth?
I nailed it. But I'm a hammer everything to me is a nail. :cool:
 

wrinke

Feb 25, 2023
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Because if it was me I would be very proud of my new scope and probes.
Pretty close to the truth?
I nailed it. But I'm a hammer everything to me is a nail. :cool:
I m not proud at all of my new oscilloscope. I didn t expect too much from the cheapest oscilloscope of Amazon .
A Little bit of noise, ok, but that big spike.... The relays are far from oscilloscope, 3m more or less. Can E filed from small realys cover that distances?! If not, mean that all noise came from power supply plug. In this case, can that spike
damage other electronic devices in my home!?
 

Delta Prime

Jul 29, 2020
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damage other electronic devices in my home!?
It would have done it by now I think you'll be okay.
Having the cheapest O'scope is better than no scope.
3 m approximately 10 ft certainly the probe could pick that up.
You can always wear foil hats to protect yourself that's what I do. ;)
By the way do you have a diode place across the coil of your relay to protect against back EMF that'll that'll cause a spike when the electro magnetic field collapses when the coil is de-energized?
Also... Do you have your microcontroller in the room. Cuz I noticed you have another thread going.
 
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danadak

Feb 19, 2021
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Using scope probes :

On probing, 15 cm for high speed stuff, which a micro is asking for misinterpretation.
See the following on probing considerations (section page 46 on ground lead length) :

View attachment 58252




Also do the scope probe compensation adjustment to make sure thats addressed.

In case you have to make measurements on AC line related stuff, attached.
This will prevent you from burning out the front end analog processing in your
oscilloscope.

Your oscilloscope is your stethoscope, take the time to read the ap notes, they
will save you a lot of misery.

Regards, Dana.
 

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wrinke

Feb 25, 2023
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You can always wear foil hats to protect yourself that's what I do.
I will follow your suggestion :)
By the way do you have a diode place across the coil of your relay to protect against back EMF that'll that'll cause a spike when the electro magnetic field collapses when the coil is de-energized?
The relays are like this https://catalogo.hager-bocchiotti.i...-misura/rele-passo-passo/2-na/epn520/1655.htm, they are controlled in AC 250v

Do you have your microcontroller in the room. Cuz I noticed you have another thread going.
Yes, I discover the interference when my wife switch on the room light during my investigations on the micro based circuit.


Do you have explanation why, if I short probe (head with its ground), there isn't any kind on noise, instead, if I connect probe with + and - of AA battery, the spike on relay switch, appears?
 

wrinke

Feb 25, 2023
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On probing, 15 cm for high speed stuff, which a micro is asking for misinterpretation.
See the following on probing considerations (section page 46 on ground lead length) :
]



Also do the scope probe compensation adjustment to make sure thats addressed.

In case you have to make measurements on AC line related stuff, attached.
This will prevent you from burning out the front end analog processing in your
oscilloscope.

Your oscilloscope is your stethoscope, take the time to read the ap notes, they
will save you a lot of misery.

Regards, Dana.
This message I think was related to other topic :)
Yes, the probe is well compensated, I will try to repeat the measurement with shorter ground and I will add 0.1µF near to micro pins, as you suggest me previously

In case you have to make measurements on AC line related stuff, attached.
This will prevent you from burning out the front end analog processing in your
oscilloscope.
Sorry, but I didn't understood well what prevent me to burn my oscilloscope!?
 

danadak

Feb 19, 2021
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If you read the ap note on Isolated measurements that will describe the
ground problem when doing measurements on non isolated systems, like
a SMPS for example.




Regards, Dana.
 

wrinke

Feb 25, 2023
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If you read the ap note on Isolated measurements that will describe the
ground problem when doing measurements on non isolated systems, like
a SMPS for example.




Regards, Dana.
I watch video just as killtime, because are concepts that already know.....but as he told "BANG" I wasn't aware that USB is earth referenced. There is always something to learn, thanks Dana
 

danadak

Feb 19, 2021
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I am long overdue at getting a isolation transformer, now looking into DIY using
old microwave oven transformers. Youtube has some videos on this topic.

New scopes, a new series from Tektronix, offering battery operation which is a
great way of getting isolation. One can always use a car battery and an inverter,
but thats a recipe for noise I would posit coming from inverter.


Regards, Dana.
 

crutschow

May 7, 2021
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Do you have explanation why, if I short probe (head with its ground), there isn't any kind on noise, instead, if I connect probe with + and - of AA battery, the spike on relay switch, appears?
Likely because you are introducing an antenna from the battery and ground wire loop.
So the problem is not your 'scope, it's the connections.
 
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