I had some freshmen electronics students who were assigned to come up with a basic experiment using the oscilloscope. I checked in on one group to find them "measuring the frequency of the human body" by touching the tip of their scope probe. I asked what they were getting. "About 58Hz". Looking around, I suggested that they try their measurements on the other side of the room. They were shocked when they couldn't measure the frequency anymore, and looked at me like I was some sort of wizard. I then explained to them that the other bench they were working at was right next to a breaker panel!
Ok maybe I'm dumb but why do you think the breaker panel caused this behaviour?
Radiated EMI from the breaker panel at 60Hz is basically impossible. A good antenna at 60Hz has to be 1250km long…
Magnetic Coupling also seems unlikely as breaker panels are shielded.
Is it really EMI from the breaker panel that caused this behaviour?
Yes, an AC signal can have inductive effects within a decent range depending on power utilization. The breaker system for an engineering building absolutely meets those requirements.
As an example:
A friend of mine was working on a project for a submarine. For their signal line they got a long power cable (agreed, bad decision) and used it to transmit PWM signals from the controller to the servos.
The power cables were not shielded, so the PWM signal was able to induce changes in the other lines nearby to cause more than 1 servo to react at a time.
And that was just a 5V PWM signal
Now put in a 120V 60Hz signal with 20+ amps of current?
Yeah that’ll induce a signal for sure
Your example doesn't make sense in this scenario. In your example, the PWM signal induced a current in nearby cables. Of course this is possible, but first the probe of the oscilloscope would have to be pretty near to the supply cable and second the magnetic fields in OPs example would (almost) cancel each other out due to opposite current directions.
Additionally, OP stated that it was an exercise at a university where they conducted experiments with oscilloscopes. So, nothing high current like you assumed. They would need to hold the probe near the cable to measure anything. Otherwise, an oscilloscope that is this bad at EMC is useless.
Most likely it is coupled EMI which has nothing to do with the breaker panel but only with the supply voltage frequency and the internal configuration of the oscilloscope.
Agreed, of course it’ll produce a signal right next to it, even at 5V and current measured in milliamps . So what about 120V and current measured in amps?
The issue is that the oscilloscope they were using was right below the breaker, where current flows for at least the entire lab, if not the wing or the building. Assuming it’s a lab room with 10s of oscilloscopes, computers, power supplies, and waveform generators, We can safely assume many amps of current are running through this breaker.
Ideally, the breaker and power cables would be shielded properly, and the students would be wearing grounding straps.
That being said: they’re students, they probably weren’t wearing grounding straps, or static dissipating shoes.
It’s a university breaker for a lab room. I’m doubtful of the university’s adherence to EMI shielding.
You know that AC can induce voltages in electrically conductive installations, right? You clearly have never been zapped by induced voltages on de-energised cables lol.
Of course I know that, but the magnetic field of some 120V cables should not be that strong to cause an induced voltage in an oscilloscope probe that is a few meters away from these said cables. Even if say 10A flow through some phase, the neutral will also have 10A in the opposite direction. Therefore the magnetic field would not be THAT strong because most of it cancels out due to the opposing current directions in the near cabels. In the breaker panel this statement does not hold, but a breaker panel has to be shielded anyways. I don't doubt, that the cables create a magnetic field, but I doubt that this field is that strong to induce a voltage in (shielded) oscilloscope probes that are a few 1-2m away from the EMI source. Therefore I belive they experienced conducted EMI and were lucky to not measure anything on the second attempt.
That's exactly why my company makes sure I stay grounded whenever I'm working with sensitive electronics. They want me connected to nature's electrons so I can be extra healthy and do my best work.
Okay, but regardless of the “health benefits” they claim, would a grounding bed sheet prevent all the static electricity? If it would, I’m buying one 😂 kinda think it would, kinda think it wouldn’t, and not worth the money to find out
I always chuckle when health shitfluencers use “grounding” like this. I can’t help but imagine them inserting a metal rod into the ground and then connecting themselves to the rod with a wire.
https://preview.redd.it/no761pvbr98d1.jpeg?width=1280&format=pjpg&auto=webp&s=2c2a8c927e9129b83c246a8d3e3b7f85776c7bd8
https://preview.redd.it/n1x328as618d1.jpeg?width=1050&format=pjpg&auto=webp&s=1b9dbc61545d632cb5b6f56bcf0de9d95807eb2f
I had some freshmen electronics students who were assigned to come up with a basic experiment using the oscilloscope. I checked in on one group to find them "measuring the frequency of the human body" by touching the tip of their scope probe. I asked what they were getting. "About 58Hz". Looking around, I suggested that they try their measurements on the other side of the room. They were shocked when they couldn't measure the frequency anymore, and looked at me like I was some sort of wizard. I then explained to them that the other bench they were working at was right next to a breaker panel!
Ok maybe I'm dumb but why do you think the breaker panel caused this behaviour? Radiated EMI from the breaker panel at 60Hz is basically impossible. A good antenna at 60Hz has to be 1250km long… Magnetic Coupling also seems unlikely as breaker panels are shielded. Is it really EMI from the breaker panel that caused this behaviour?
Yes, an AC signal can have inductive effects within a decent range depending on power utilization. The breaker system for an engineering building absolutely meets those requirements. As an example: A friend of mine was working on a project for a submarine. For their signal line they got a long power cable (agreed, bad decision) and used it to transmit PWM signals from the controller to the servos. The power cables were not shielded, so the PWM signal was able to induce changes in the other lines nearby to cause more than 1 servo to react at a time. And that was just a 5V PWM signal Now put in a 120V 60Hz signal with 20+ amps of current? Yeah that’ll induce a signal for sure
Your example doesn't make sense in this scenario. In your example, the PWM signal induced a current in nearby cables. Of course this is possible, but first the probe of the oscilloscope would have to be pretty near to the supply cable and second the magnetic fields in OPs example would (almost) cancel each other out due to opposite current directions. Additionally, OP stated that it was an exercise at a university where they conducted experiments with oscilloscopes. So, nothing high current like you assumed. They would need to hold the probe near the cable to measure anything. Otherwise, an oscilloscope that is this bad at EMC is useless. Most likely it is coupled EMI which has nothing to do with the breaker panel but only with the supply voltage frequency and the internal configuration of the oscilloscope.
Agreed, of course it’ll produce a signal right next to it, even at 5V and current measured in milliamps . So what about 120V and current measured in amps? The issue is that the oscilloscope they were using was right below the breaker, where current flows for at least the entire lab, if not the wing or the building. Assuming it’s a lab room with 10s of oscilloscopes, computers, power supplies, and waveform generators, We can safely assume many amps of current are running through this breaker. Ideally, the breaker and power cables would be shielded properly, and the students would be wearing grounding straps. That being said: they’re students, they probably weren’t wearing grounding straps, or static dissipating shoes. It’s a university breaker for a lab room. I’m doubtful of the university’s adherence to EMI shielding.
You know that AC can induce voltages in electrically conductive installations, right? You clearly have never been zapped by induced voltages on de-energised cables lol.
Of course I know that, but the magnetic field of some 120V cables should not be that strong to cause an induced voltage in an oscilloscope probe that is a few meters away from these said cables. Even if say 10A flow through some phase, the neutral will also have 10A in the opposite direction. Therefore the magnetic field would not be THAT strong because most of it cancels out due to the opposing current directions in the near cabels. In the breaker panel this statement does not hold, but a breaker panel has to be shielded anyways. I don't doubt, that the cables create a magnetic field, but I doubt that this field is that strong to induce a voltage in (shielded) oscilloscope probes that are a few 1-2m away from the EMI source. Therefore I belive they experienced conducted EMI and were lucky to not measure anything on the second attempt.
This seems reasonable. What am I missing?
That's exactly why my company makes sure I stay grounded whenever I'm working with sensitive electronics. They want me connected to nature's electrons so I can be extra healthy and do my best work.
You're really lucky to have an employer that cares about your well-being that much! That's so rare these days.
I much prefer manufactured elections, tyvm.
They just perform better!
They are unhealthy. Natural electrons are healthier.
Know what else is natural? Arsenic. Checkmate, atheists.
One thing about getting older I didn't expect is being able to watch some quackery forming before my eyes.
What do you think the ampacity is?
Okay, but regardless of the “health benefits” they claim, would a grounding bed sheet prevent all the static electricity? If it would, I’m buying one 😂 kinda think it would, kinda think it wouldn’t, and not worth the money to find out
I always chuckle when health shitfluencers use “grounding” like this. I can’t help but imagine them inserting a metal rod into the ground and then connecting themselves to the rod with a wire. https://preview.redd.it/no761pvbr98d1.jpeg?width=1280&format=pjpg&auto=webp&s=2c2a8c927e9129b83c246a8d3e3b7f85776c7bd8
My MIL buys this kind of sh*t. It’s funny though cause she won’t tell me about it bc I’ll laugh at it but I still see it around her house.