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Is our body a voltage Source?

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Electronman

New Member
Hello,

Why My digital voltmeter counts and shows me several digits changing by time while I touch it by my hands?
My professor told me it's because our body has voltage??!

What about when it acts like an Antenna?
 

tcmtech

Banned
Most Helpful Member
True.
A good digital voltmeter set to its lowest range can usually pick up the small electrical potential variations form place to place going through our skin when muscles are contracting and relaxing.:)
Try using two damp electrodes placed at different places on your arm and then flex different muscles. With a bit of testing and practice you can repeatedly and accurately raise, lower and reverse the polarity of the tiny voltages present on your skin.

Use an amplifier circuit to bring that voltage up high enough and you can use it to control simple circuits just with the correct muscle movements! ;)
 

bryan1

Well-Known Member
Use an amplifier circuit to bring that voltage up high enough and you can use it to control simple circuits just with the correct muscle movements! ;)


That sounds like too much work. Just eat a few tins of baked beans then point ya rear end towards a small wind genny. The only muscle used there is quite soothing after a few tins of baked beans.
 

ke5frf

New Member
Thanks, So it is due to Muscles of human body right?

What about the ability of humans body to act as an antenna?


No, my understanding is that voltages you may read on your skin are from charges due to our body's capacitance. We store potentials on the surface of the skin and discharge them frequently. This can fluctuate due to humidity and environmental conditions. This is why solid state devices made with field effect technology are especially vulnerable to our touch and should be handled with ESD techniques. Tiny discharges of hundreds of volts can leave our body when we touch objects without us even being aware.

This is also why we have an effect on antennas, it is called capacitive coupling.
 

crutschow

Well-Known Member
Most Helpful Member
The body can act as an antenna since the body is conductive and any conductive material can be an antenna.
 

lmd822

New Member
No, my understanding is that voltages you may read on your skin are from charges due to our body's capacitance. We store potentials on the surface of the skin and discharge them frequently. This can fluctuate due to humidity and environmental conditions. This is why solid state devices made with field effect technology are especially vulnerable to our touch and should be handled with ESD techniques. Tiny discharges of hundreds of volts can leave our body when we touch objects without us even being aware.

This is also why we have an effect on antennas, it is called capacitive coupling.
The human body's capacitance is sometimes responsible for changes in electrical potential, but all points in space in the entire universe have electrical potential. If you had a meter sensitive enough, you could measure the voltage between two points in air. However, this voltage is usually so small that your run-of-the-mill meter can't even come close to detecting it.

To answer the OP directly:

Yes, the human body has voltage, and sometimes this voltage is measurable. The voltage generated by the flexing of muscles is sometimes measurable, as is the voltage generated by neurological processes. Even single cells in your body have a voltage, but that voltage is usually too small to show up on meters.
 
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Sceadwian

Banned
ke5 modern meters have input impedance of at least a megaohm, he could be reading real voltage.
Nerve impulses are chemically influences but electrical in overall nature.
 

ke5frf

New Member
ke5 modern meters have input impedance of at least a megaohm, he could be reading real voltage.
Nerve impulses are chemically influences but electrical in overall nature.

Yes, I know that digital meters have high input impedances. And I never said he wasn't reading real voltages. Why wouldn't the potentials present on the human body be real?
 

Sceadwian

Banned
Not so much that it wasn't real, but that it wasn't from within the body. The human body has the potential to create voltages not just as a passive capacitive device, I thought you were saying that when you started the sentence with no. Especially considering that the electrical impulses to muscles are just that, chemically derived potential differences followed by current flow triggering cell reaction. Mind you the muscle reaction itself isn't directly actuating muscles but triggering them to actuate. I thought you were infering than any voltage read from the human body was of an external origin and we were merely passive components.
 

ke5frf

New Member
Ah, I do not disagree with you that the human body creates its own voltages (micro and milli)...of course, we wouldn't be able to think or control or sense our tissues. But these are internally produced and the epidermal layer, when clean, has a resistance of at least 500 to millions of ohms.

The voltages you can read on your body with your electricians voltmeter are AC coupled voltages from power lines and all the AC sources surrounding us.
 

ke5frf

New Member
The human body's capacitance is sometimes responsible for changes in electrical potential, but all points in space in the entire universe have electrical potential. If you had a meter sensitive enough, you could measure the voltage between two points in air. However, this voltage is usually so small that your run-of-the-mill meter can't even come close to detecting it.

To answer the OP directly:

Yes, the human body has voltage, and sometimes this voltage is measurable. The voltage generated by the flexing of muscles is sometimes measurable, as is the voltage generated by neurological processes. Even single cells in your body have a voltage, but that voltage is usually too small to show up on meters.

A run-of-the-mill fluke meter does a fine job of picking up voltages coupled to your skin from the surrounding environment.
 

Sceadwian

Banned
AC coupled voltages read in DC mode?
 

ke5frf

New Member
Man, I see nowhere in the OPs post that mentions DC.

He asked if the voltages he reads on his meter are from his muscles. He didn't specifiy which function he read it with. I have held my voltmeter to my skin before (yes, this has come up over the years) and read AC voltages (up to and sometimes over a volt) at 60 Hz.

Anything read on the DC scale is random noise and not effected by touching the meter or simply holding it in mid air.
 

Sceadwian

Banned
For the sake of science my meters probes are in good contact with my tongue just now left and right side. On AC (200mv scale) it reads 0.0mv. When it's on DC I get between 10 and 50mv depending on how hard I'm biting it against my tongue. Removing the meter leads I can't get anything but small mv spikes on DC where as against my tongue the DC signal was sustained. No AC readings against my body were ever more than a few mv's although they jumped to 30mvs sustained when floating. Higher when moved around.
 
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lmd822

New Member
A run-of-the-mill fluke meter does a fine job of picking up voltages coupled to your skin from the surrounding environment.
I was trying to give a more general explanation, based on physics, not describe location specific phenomena. Perhaps I should have been more specific with my example. Let's say you go 4 miles up into the atmosphere to perform this measurement, where any AC coupling from man-made sources would be reduced by several powers of 10.
 
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ke5frf

New Member
For the sake of science my meters probes are in good contact with my tongue just now left and right side. On AC (200mv scale) it reads 0.0mv. When it's on DC I get between 10 and 50mv depending on how hard I'm biting it against my tongue. Removing the meter leads I can't get anything but small mv spikes on DC where as against my tongue the DC signal was sustained. No AC readings against my body were ever more than a few mv's although they jumped to 30mvs sustained when floating. Higher when moved around.

Also for the sake of science, I used my Fluke 787 to conduct an experiment just now. On the AC scale, with one lead touching my skin and the other lead touching grounded metal, I read approx. 700 millivolts. I switched to the frequency function and read 60 Hz AC. Removing the lead from my skin and leaving the other lead contacting ground dropped the voltage to fluctuating between 50 mV and 150 mV.

I conducted another experiment using the DC scale. I replicated the tongue experiment by placing the two leads on either side of my tongue. I got fluctuating readings between 100 to 120 mV DC (positive). I swapped the leads, placing them in the same position on my tongue as before, but using the opposite lead configuration, and I still got 100 to 120 mV DC (positive) DC voltage has polarity with respect of one voltage source to another. If 120 mV of DC potential exists from one point on my tongue to the other, then there should be a polarity change when I swap leads. There is no polarity change when I do so. I repeated this a dozen times with no difference in outcome.

The DC scale experiment is flawed, because we have no frame of reference from which to measure voltages on our bodies. Where is ground or low potential? How do we determine where the higher potential exists vs the lower one? This is DC voltage we are supposed to be measuring, but it doesn't measure as DC. If I measure two points on a circuit, in order for me to detect a voltage I have to have a higher potential vs a lower potential. If I detect a voltage, swapping the leads will demonstrate a polarity reversal each and every time if the voltage is DC. Yet the DC experiment on my body does not prove where sources of higher potential exist vs lower potential. Furthermore, the test isn't repeatable. After turning my meter off and back on and retesting, the voltages I read changed.

The problem with this discussion is a failure to recognize how a voltmeter functions and what is required for a reliable measurement. My AC test was a test vs a known reference, grounded metal. I detected nearly 3/4 a volt of AC potential between my body and that ground point. I can conclusively say that this is coupled AC from MAINS sources, because the frequency function verifies 60 Hz.

I am not a medical doctor, but I do understand DC electricity and my judgement says that we are NOT reading anything more than random noise or static potentials on our skin with the DC meter. In fact, I just now waved the leads around in the air and as I moved them the mV scale jumped all over the place without physically contacting anything. If someone can demonstrate how the DC meter is referencing its reading against a lower potential, I might be inclined to believe the noise we see is human produced rather than human coupled.
 

ke5frf

New Member
For the sake of science my meters probes are in good contact with my tongue just now left and right side. On AC (200mv scale) it reads 0.0mv. When it's on DC I get between 10 and 50mv depending on how hard I'm biting it against my tongue. Removing the meter leads I can't get anything but small mv spikes on DC where as against my tongue the DC signal was sustained. No AC readings against my body were ever more than a few mv's although they jumped to 30mvs sustained when floating. Higher when moved around.

Specifically, when you performed the AC experiment, you were improperly using your meter.


Edit:

This discussion sparked my curiosity, so I did some Google research to learn a little more about all of this muscle voltage stuff to see if there is some kind of correlation with these DC voltmeter readings. I don't debate or discuss these things for no reason or just to be argumentative. I truly like to learn and understand and uncover the truth. If I happen to be correct after the dust settles, it is only a verification of my prior understanding, not a "one up" thing.

I found an easy to understand discussion of Electromyography here :**broken link removed**

Electromyographs are specialized medical devices specifically designed to pick up the human produced voltages in the muscle tissues. There are surface methods as well as direct contact with needles. I found this quote interesting:

"single muaps have amplitude of 100 microvolts
signals detected by surface electrodes are in range of 5 mV
signals detected by indwelling electrodes are in range of 10 mV

Amplifier impedance
must be considerably higher than the impedance of the electrode/skin or electrode/muscle interfaces. Since indwelling electrodes have very high impedances (due to low surface area), very high amplifier impedances are necessary.
common mode rejection

Even when leads are shorted together, a signal of 20 - 50 microvolts may result from ambient electromagnetic energy, induced by nearby machinery or electrical lines. The body itself is like an antenna that picks up ambient electromagnetic signals, including the 60 Hz signal from ordinary house current. This "hum" is in the middle of EMG frequency range; we can't filter it."
___________
Conclusion. Even with specifically designed equipment with filtering and tailored response, muscle voltages using surface techniques (which requires electrolyte gel applied at the electrode site) are only in the 5 mV range. Electromagneticaly induced or coupled voltages are in the response range of EMG devices and filtering them is a challenge.

I find it difficult to believe that an electrician's voltmeter applied to the fingertips or tongue willy nilly is picking up anything from human produced electricity.
 
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