NO, the "potential equalization conductor" must connect to the patient and the equipment operator. THOSEare the sections of the system that must be at the same potential, whatever it may be. This is not guarding against mains power shocks, this is providing the same zero volts reference for all parts of the instrumentation system.

drjohsmth said the patient must not be connected to earth ground while you (MisterBill2) said the patient should be connected to earth ground. So today I read all about it. I didn't know at first if my g.USBamp ground was connected to the casing ground. I tried to avoid using my multimeter to check to avoid static probing the electrode ground and casing, but no definite info anywhere. I eventually connected my antistatic wrist band to the water tank and probed the g.USBamp I found out the electrode ground is NOT connected to the unit casing in the g.USBamp. Did you mean a separate earth conductor must be connected to the patient to minimize noises (like capacitive coupling)??



I have another bioamplifier called BMA-200 (above). The main unit has the electrode ground connected to the casing and earth ground. But they have a separate ISO-Z isolation head stage to separate the earth ground from the electrode ground (to make floating ground). BUT the ISO-Z has terrible noises added to signal because the isolator chip noises is plenty in the microvolt region. Therefore I avoid using the ISO-Z and just the main amplifier, which has very excellent signal even better than the g.USBamp.

My question. If you don't use floating or isolation in the ground. The signal would be better not only because of the lack of the ISO chips noises but because of lessened capacitive coupling due to the patient, unit and operator having same potential, is this proven??

 

WRONG!!!! I did not say anything about an earth ground connection, but rather that the patient, equipment operator, and the equipment inputs must all be at the same potential, whatever that is. That is totally different!!

Connecting the patient to the earth-ground assures that any leakage current can deliver a fatal shock.

 

I just used multimeter a while ago to check the continuity of the potential equalization conductor and the unit casing, I was mistaken, they are connected.

I eventually connected my antistatic wrist band to the water tank and probed the g.USBamp I found out the electrode ground is NOT connected to the unit casing in the g.USBamp.

So which is it?
I don't think it matters though. What is important is that the patient, the operator and the amplifier reference point have the same potential, NOT connected to mains ground.

 

It seems to me that the whole thread has been taken over by the arguments about possible shock hazards, while the original questions were about the cause and cures of mains-carried noise and mains frequency harmonics.
Based on the various TS statements, it appears that the current mains power contains harmonic energy, that is apparently coupled thru a noisy switching power supply, onto the DC supply that claims to be medical grade, and into the interface amplifier digital output to a computer.

So now there appears that we have an argument about the need for every portion of everything being solidly tied to the green-wire earth ground. Certainly the thread has drifted.

 

WRONG!!!! I did not say anything about an earth ground connection, but rather that the patient, equipment operator, and the equipment inputs must all be at the same potential, whatever that is. That is totally different!!

Connecting the patient to the earth-ground assures that any leakage current can deliver a fatal shock.

When I used the BMA-200 and even the g.USBamp, I always used batteries. The reasons I asked so much about AC adaptor is because most g.USBamp owners used AC adaptor and want to understand how they are connected. And second. I need to know whether the harmonics come from the mains or the supply (any final tests to determine which is the case?). Because if it comes from the main, it means my entire room has harmonics capacitive coupling too that can drown the signal. My signal is swimming in the noise floor, so short of a faraday cage which I can't afford. I need to understand the capacitive coupling if it contains harmonics.

Anyway. When I used the antistatic wrist band with 10 Megaohm resistor. Do you consider myself as connecting to earth-ground? Because when I connected to the g.USBamp via battery, the ripples in the display gets less when I connected the antistatic wrist band. This means my body has capacitive coupling which can be shunted to earth ground?? Can this happen?

You know using purely batteries will have no problem connecting myself to earth ground. I can connect the earth ground to a small ball that I will hold and if in case there is fault current from my neighbor passing thru earth then if I get shock, i'd drop the ball disconnecting the earth ground. Since I will never use the AC adaptor, i will have no risk of leakage current from the mains since I used purely batteries.

 

So which is it?
I don't think it matters though. What is important is that the patient, the operator and the amplifier reference point have the same potential, NOT connected to mains ground.

I mean the potential equilization conductor is connected to the g.USBamp unit metal casing (I'm 100% sure of it after massive multimeter probe), but its electrode ground is NOT connected to them (also 100% sure of this as I did massive multimeter probe). That means its electrode ground is floating. Of course this makes sense considering it is a class CF (Cardiac Floating) unit for use in medical surgery. Btw.. There is unexplained DC offset below 5Hz. Can floating ground contribute to more DC offset? My BMA-200 doesn't have DC offset. It is pure instrumentation amplifier. The reason I still use the g.USBamp is because other researchers used it too.

Don't miss the last message whether using antistatic wrist band with 10 Megaohm is like connecting to earth potential. Btw.. I forgot to ask. I don't know if the BMA-200 has better signal because it main unit electrode ground connects to earth ground, (using batteries so safe). Is there a difference if I hold a steel ball connected to earth ground in the g.USBamp using pure battery versus if the g.USBamp used earth potential ground in the electrode (which it doesn't)? I think having a bonafide earth potential ground in the electrode and the unit in battery mode is the best of all worlds? Note connecting to earth potential is dangerous only if the unit source is AC, but not batteries.

 

You are absolutely wrong about being safe while holding a ball in your hand.

Electrical stimulation causes muscles to contract. Your grip on the ball gets tighter and you will not be able to let go voluntarily. This is one of the primary ways how people get electrocuted.

 

You are absolutely wrong about being safe while holding a ball in your hand.

Electrical stimulation causes muscles to contract. Your grip on the ball gets tighter and you will not be able to let go voluntarily. This is one of the primary ways how people get electrocuted.

I don't know if the ball is even necessary. I will of course use batteries only. I never used AC adaptor on the BMA-200 but only NiMh 1.2V batteries in one year of use. And I used powerbanks on the g.USBamp. All the AC adaptor and harmonics concerns is just to understand their capacitive coupling versions (if the mains has harmonics).

When we take a bath. We don't worry about getting shock from fault current running in the earth, do we? So with a powerbank powered bioamplifier, why should I be worried about earth ground? Of course it is totally different matter when it involves AC which can electrocute the person if the AC adaptor got detached from ground and the hot capacitor current moves to your body. But I will never use AC adaptor again (thanks to drjohsmith warning) and will always use batteries from now on. So is the ground ball even necessary? I can just remove my slippers and touch my feet to the floor when using purely BATTERY powered bioamplifiers.

 

The anti-static wrist strap has a 1 MΩ or 10 MΩ resistor in series with the cable.
The purpose of the wrist strap is to bleed away any electro-static charge that has built up on your body. The purpose of the resistor is to reduce the current in the event that you come in contact with a power source. The wrist strap brings you and the ground to equipotential provided that there is no active power source involved. If your "grounding point" is part of an active power source then all bets are off.

When you take a bath you have no concern about getting a shock because there is no power source involved.
However, if your bath is a jacuzzi, hot tub, jet tub, etc., the tub is required by electrical code to be electrically powered via a GFCI.

 

ALL of the electrical shocks that I have received over the years resulted in a rapid jerk away from the source.

 

The anti-static wrist strap has a 1 MΩ or 10 MΩ resistor in series with the cable.
The purpose of the wrist strap is to bleed away any electro-static charge that has built up on your body. The purpose of the resistor is to reduce the current in the event that you come in contact with a power source. The wrist strap brings you and the ground to equipotential provided that there is no active power source involved. If you "grounding point" is part of an active power source then all bets are off.

When you take a bath you have no concern about getting a shock because there is no power source involved.
However, if your bath is a jacuzzi, hot tub, jet tub, the tub is required by electrical code to be protected by a GFCI.

So the wrist band is enough for grounding when purely batteries used. Ok.

The odd thing is that when the AC adaptor ground was not used, and there were harmonics... wearing the wrist band makes the ripples worse.. maybe the wires attracting capacitive coupling.

But when using batteries. Wearing wrist band removes small ripples left.

If I'll shut down my main breaker and all electricity in home is off when I used the bioamplifier with batteries in laptop in batteries, I guess the capacitive coupling would be gone? Or would you say the neighborhood power lines capacitive coupling would affect me too?

Btw.. capacitive coupling in the body can be shunted by earth grounding or wear the antistatic wrist band for example?

 

You are mixing different things.

The antistatic wrist band is worn to prevent damage from ESD.
Grounding to reduce EMI is a different issue.

On top of that, safety to a person connected to electrical equipment is another issue.

 

You are mixing different things.

The antistatic wrist band is worn to prevent damage from ESD.
Grounding to reduce EMI is a different issue.

On top of that, safety to a person connected to electrical equipment is another issue.

Yes things got mixed up because we discussed them together. To put things in proper perspective. I googled and read this:

Potential Equalization Conductors - Elsmar Cove Quality and Business Standards Discussions

"Potential equalization was originally intended for cardiac areas where even small potentials (e.g. 0.1V) could theoretically cause electric shock, e.g. open heart surgery, cardiac catheter procedures."

So its purpose is not to eliminate static?

drjohsmith described about equalizing potentials to avoid static. And we discussed about the potential equalization conductor at the back of unit so I thought it is for avoiding static and avoiding interference. So, let's distinguish.

1. Potential equalization conductor - purpose is to prevent small potentials to harm the heart or patient.. this must NOT be earthed.

2. Anti static conductor equalization - to make objects in same potential so statics won't flow, thist must be earthed.

3. EMI conductor equalization - to avoid capacitive coupling and shunting it.


So if I connect the potential equalization conductor (connected to unit casing) to the water pipe along with my antistatic wrist.. the purpose is antistatic protection, and not the original Potential equalization conductor use anymore since I am using battery. Right?

What i need to pursue now in other forums site or another thread is about EMI grounding. I thought EMI also occurs due to potential difference and equalizing potentials will eliminate it? No? But then, if I shut off the mains breaker, it will equalize potential to 0 and hence eliminate capacitive coupling, isnt it?

To make it not off topic, is harmonics in the main not normal elsewhere in the world? Our country initially imported broken or used AC systems in the United States that is why our transformer hot lines are 110V with respect to neutral instead of 220V to ground yet our homes use only 220V.

 

Yes things got mixed up because we discussed them together. To put things in proper perspective. I googled and read this:

Potential Equalization Conductors - Elsmar Cove Quality and Business Standards Discussions

"Potential equalization was originally intended for cardiac areas where even small potentials (e.g. 0.1V) could theoretically cause electric shock, e.g. open heart surgery, cardiac catheter procedures."

So its purpose is not to eliminate static?

drjohsmith described about equalizing potentials to avoid static. And we discussed about the potential equalization conductor at the back of unit so I thought it is for avoiding static and avoiding interference. So, let's distinguish.

1. Potential equalization conductor - purpose is to prevent small potentials to harm the heart or patient.. this must NOT be earthed.

2. Anti static conductor equalization - to make objects in same potential so statics won't flow, thist must be earthed.

3. EMI conductor equalization - to avoid capacitive coupling and shunting it.


So if I connect the potential equalization conductor (connected to unit casing) to the water pipe along with my antistatic wrist.. the purpose is antistatic protection, and not the original Potential equalization conductor use anymore since I am using battery. Right?

What i need to pursue now in other forums site or another thread is about EMI grounding. I thought EMI also occurs due to potential difference and equalizing potentials will eliminate it? No? But then, if I shut off the mains breaker, it will equalize potential to 0 and hence eliminate capacitive coupling, isnt it?

To make it not off topic, is harmonics in the main not normal elsewhere in the world? Our country initially imported broken or used AC systems in the United States that is why our transformer hot lines are 110V with respect to neutral instead of 220V to ground yet our homes use only 220V.

for reference
the comments above about static and ecg attributed to me by the op are a contortion of the truth ,

@Secan
you asked about ac harmonics and why differential amplifier can not eliminate them.
has this question been answered ?

 

for reference
the comments above about static and ecg attributed to me by the op are a contortion of the truth ,

@Secan
you asked about ac harmonics and why differential amplifier can not eliminate them.
has this question been answered ?

When i mentioned "we" i mean Alec_t and I discussed about the potential equalization conductor, not with you so it was not contortion of truth.

Harmonics has been answered enough for me to ask questions about capacitive coupling versions of harmonics in mains in other sites.

Many thanks for all answers and tips. Enjoy your trips.

 

When i mentioned "we" i mean Alec_t and I discussed about the potential equalization conductor, not with you so it was not contortion of truth.

Harmonics has been answered enough for me to ask questions about capacitive coupling versions of harmonics in mains in other sites.

Many thanks for all answers and tips. Enjoy your trips.

we're all in agreement then @Secan
I always enjoy traveling to jobs even after 40 plus years ,
I look forward to seeing your new post subject.

having read your confusion and discusions on static , charge , voltages, earth , circuit breakers and equipotential, you have encouraged me to write an app note for the University. thanks for the idea,

 

You keep calling it AC harmonics.
I prefer to call it EMI.

I was testing a crystal radio circuit to provide guidance on another thread. The radio reception received a lot of EMI. It turns out that the noise went away when I turned off the room lights which has a light dimmer switch.

Also it is common occurence that turning off fluorescence room lights reduces EMI in sensitive circuits.

I detected EMI from someone’s computer one floor below me. Even my temperature controlled soldering iron station can be troublesome.

 

You keep calling it AC harmonics.
I prefer to call it EMI.

I was testing a crystal radio circuit to provide guidance on another thread. The radio reception received a lot of EMI. It turns out that the noise went away when I turned off the room lights which has a light dimmer switch.

Also it is common occurence that turning off fluorescence room lights reduces EMI in sensitive circuits.

I detected EMI from someone’s computer one floor below me. Even my temperature controlled soldering iron station can be troublesome.

Lower order harmonic voltages on mains power circuits are entirely different from what is commonly referenced as "EMI".
Mains frequency harmonics are primarily generated by non-linear loads on the mains power line, such as the input rectifiers on switching power supplies, and the switcher speed controls for electric motors, and similar systems.
Those harmonics are integral multiples of the mains frequencies, as opposed to the broad spectrum of general interference noise..
The Pain Point of those harmonics is the distortion of the current waveform in distribution systems, because the magnitude is much greater than that of the broad spectrum noise.

 

Line noise can propagate through wiring as well as wirelessly, with or without harmonics.

 

It is unlikely that the lower order harmonics that are integral multiples of the mains frequency, will radiate very far. BUT certainly they can persist in the wiring for quite a distance, since there is a lot more power present in the harmonics.