Mosquito Sound

[w_tom]

An adjacent surge protector contains a device that does not
stop surges. It simply shunts all wires together during that
surge. A surge shunted from one wire to all others goes
where? Remember, the destructive surge seeks earth ground.
It now has more paths to find earth ground, destructively, via
the adjacent computer. What kind of protection is that
adjacent protector? Ineffective.

Telcos prefer their protectors located 50 meters from a
$multimillion switching computer. Protectors adjacent to the
computer might only shunt the surge to earth through that
computer. Many cable companies now add additional
restrictions to how cable is installed. Connection from cable
to earth ground must be significantly shorter than connection
from same point to TV or cable modem. Why? Effective
protector is distant from transistor and adjacent to earth
ground.

A surge protector is only as effective as its earth ground.
Effective protectors make a 'less than 10 foot' connection to
earth. No plug-in protector will make that connection. Just
another reason why plug-in protectors are so ineffective.
Just another reason why plug-in protector manufacturers avoid
all discussion about earthing. They don't claim to protect
from that type of surge.

Your example of an adjacent power strip protector works IF
destructive surges are normal mode. Destructive surges are
longitudinal mode. That means a surge shunted by the power
strip will seek many paths back to earth ground - including
destructively through a computer modem. The resulting error
message may be 'No Dialtone Detected'.

Damage you demonstrate inside a modem is classic of a surge
that enters on AC electric. Remember primary school science.
First electricity must flow through everything in that
circuit. Only later does something fail. A complete circuit
from cloud to earth is fully energized. Then the modem
fails. Classic modem damage is a surge that enters on AC
electric, passes through modem, then outgoing to earth ground
on phone line. This surge often damages the modem's DAA
section - the phone wire side of modem.

Many assume surges act like ocean waves. The surge destroys
the first component encountered? Of course not. Surge first
travels through everything in the circuit. Only then does
something fail. A failed DAA section does not say where surge
comes from. But many will tell us the surge ignored a telco
installed 'whole house' protector to enter modem via that
phone line. Why does surge completely ignore the phone line
'whole house' protector? Because many don't even know the
protector exists.

Surge enters on utility wire that has no 'whole house'
protector - AC electric. It then leaves (makes a complete
electrical circuit) by leaving - going to earth ground - via
phone line.

How does the phone line surge completely ignore a telephone
company installed 'whole house' protector? It must to enter
on phone line.

Your theory is good IF surge is normal mode.
Manufacturer's specifications claim to protect from normal
mode transients. Problem is that destructive surges are not
normal mode. So manufacturer forgets to mention two things:
1) plug-in protectors don't provide protection from the
typically destructive type of surge and 2) earth ground. By
forgetting to mention other types of surges, they have
promoted protection myths. Many then *assume* it protects
from all types of surges.

Destructive surges must be earthed before entering a
building. Then protection internal to all household
appliances will not be overwhelmed.

Let's see. We spend $15 or $50 to protect only one
appliance. What protects smoke detectors, intercom,
dishwasher, etc? Effective 'whole house' protector costs
about $1 per protected appliance. Furthermore it provides
protection from all types of surges. Plug-in protectors don't
make such claims.

Your example only demonstrate that plug-in protectors work
as speced. Your example forgets to discuss the type of surge
that typically damages electronics. All appliances contain
any protection that is effective adjacent to appliance.
Internal protection that requires 'whole house' protection on
every utility wire where that wire enters building.

Why are plug-in protectors often so undersized - have so few
joules? They are not really selling effective protection.
Why waste good money on more parts - more joules? Profit -
not protection - is the agenda with plug-in protectors.

Those who know surge protection do not speak of Tripplite,
Panamax, Belkin, or APC. They discuss a benchmark in surge
protection - Polyphaser. Polyphaser application notes are
legendary. Polyphaser makes a protector that has no
connection to earth ground. Distance to earth ground is so
critical that the Polyphaser protector sits directly ON earth
ground. That is zero feet to earth ground. Distance to earth
ground is that critical to effective protection. No earth
ground means no effective protection. So plug-in
manufacturers avoid the whole earthing topic all together to
sell their ineffective products. A surge protector is only as
effective as its earth ground.

Roger Johansson wrote:

w_tom <w_tom1@hotmail.com> wrote:
Some will claim that a plug-in protector would help. Again,
plug-in protector will stop or block what miles of air could
not? So very quietly, those plug-in manufacturers forget to
mention they don't even claim to protect from that destructive
type of surge. Obviously. No dedicated earth ground. They
just let others assume all surges are the same type.

A good surge protector contains one or more of these components:

A spark gap device, also called ComGap, which allows overvoltage,
charge, to jump to the earth connection.

A VDR which is slower than the Comgap, but it lowers the voltage
to zero, which protects the Comgap, this is needed if we are
talking about a mains wire, because mains delivers current until
the mains cycle reaches the zero crossing, and this current
hurts the Comgap device.

A Comgap needs to be used in series with a resistor, a big mass
type resistor, value 20 Ohm or so. The VDR is used in parallell
with this Comgap-resistor combination.

To make the protection better one can use small coils in the
signal/mains way, after the comgap. The coils stop fast voltage
changes and make the comgaps take the charge instead.

The comgaps and the VDR:s need to have the right voltage,
450Volt for a 240Volt mains wire, a 140Volt for the phone line.

It doesn't hurt the computer and other devices if the voltage
is raised a thousand volts for a short moment, as long as all
connections to it are raised together. So the surge protector
only has to keep all connections at fairly the same voltage,
even if they all are raised momentarily. What really hurts the
equipment is if one of the connections moves far away from the
other connections, because then there is a surge inside that
piece of equipment, burning some component to pieces.

That is why the extension with outlets protected by a surge
protector works. It creates a subsystem which is kept together
at virtually the same potential for all connections to that
subsystem.

When a modem is hurt by the lightning it is because the mains
connection to it and the phone connection to it are pulled
apart by thousands of volts, and that creates a damaging surge
inside the modem.

If both the mains and phone line connections to the modem first
have to pass through a protector box, where they are prevented
from moving apart too much, voltage-wise, the modem is protected.

--
Roger J.

 

[Shawn Hearn]

In article <Xns956C14101184E86336@130.133.1.4>,
Roger Johansson <no-email@home.se> wrote:

w_tom <w_tom1@hotmail.com> wrote:

Some will claim that a plug-in protector would help. Again,
plug-in protector will stop or block what miles of air could
not? So very quietly, those plug-in manufacturers forget to
mention they don't even claim to protect from that destructive
type of surge. Obviously. No dedicated earth ground. They
just let others assume all surges are the same type.

A good surge protector contains one or more of these components:

The average person does not have a "good surge protector."

 

[w_tom]

If you don't understand normal and longitudinal mode, then
you do not even have first year engineering knowledge. People
with insufficient knowledge that can promote myths about
plug-in protectors. If you think that power strip surge
protector provides more than normal mode protection, then
simply cite the manufacturer's spec. I state this knowing
full well there is no such spec. Manufacturer does not even
claim to provide that protection. Why then would you? You
are confusing normal mode with longitudinal mode.

Lets put numbers to your previous example. Lets say a small
(100 amp) transient approaches your power strip surge
protector. Let's say the wall receptacle connects to breaker
box with 50 feet of 12 AWG wire inside walls. Now let's
assume your power strip protector shunts all 100 amps to wall
receptacle safety ground. That 50 foot wire is less than 0.2
ohms resistance. But to the transient, it is something on the
order of 130 ohms impedance. Basic engineering. Wire has
impedance. 100 amps times 130 ohms puts the power strip
protector at something less than 13,000 volts. Will that
13,000 volts try to obtain earth ground via 50' safety ground
wire? Of course not. It will seek many other paths to earth
ground. One destructive path is via computer modem and
telephone wire.

So what has that power strip surge protector done? Again,
nothing complex here. The concepts only require first year
engineering. That power strip has shunted the 100 amp surge
from black hot wire onto all other wires. It has contributed
to damage of an adjacent and powered off computer.

I don't understand why you have so much difficulty with the
concept; assuming you have engineering training. These
numbers only demonstrate what has been well understood for
generations. Surge protection has always been about earthing
a surge before it can enter a building. Need I again cite how
telephone switching centers are constructed so as to not
suffer surge damage. Need I again cite the legendary
application notes of Polyphaser? What advertisement? Anyone
familiar with real surge protector knows this name as an
industry benchmark:
http://www.polyphaser.com/ppc_technical.asp

Or maybe the National Institute of Science and Technology
might help. They are not advertising. Their figure is used
to demonstrate how a fax machine is protected or may be
damaged. Again 'whole house' protector and the all so
critical single point earth ground:
http://www.epri-peac.com/tutorials/sol01tut.html

Yes, you made a good case for normal mode protection. But
that is not the type of surge that typically damages
electronics. How many industry professional citations need I
provide? A surge protector is only as effective as its earth
ground. A fact well proven even before WWII.

Roger Johansson wrote:

I feel like I am discussing loudspeaker cables with an audio hi fidelity
enthusiast.

You obviously do not understand what I am saying, but you have a lot to
say about special modes, earth connections and special brands, which
doesn't make sense from a scientific point of view.

You do not have an education in electronics, but you have a brain filled
with blurb from advertisements.

--
Roger J.

 

[Roger Johansson]

w_tom <w_tom1@hotmail.com> wrote:

Damage you demonstrate inside a modem is classic of a surge
that enters on AC electric. Remember primary school science.
First electricity must flow through everything in that
circuit. Only later does something fail. A complete circuit
from cloud to earth is fully energized. Then the modem
fails.

Many assume surges act like ocean waves. The surge destroys
the first component encountered? Of course not. Surge first
travels through everything in the circuit. Only then does
something fail.

I can take up one more point. The ideas you express above are simply
wrong, there is no scientific basis for that.

In fact, it is often a component close to the input connection which
fails, because the charge that comes rolling down the wire uses the first
possibility to unload itself to a potential closer to earth level.


--
Roger J.

 

[Jon Goguen]

In article <6a624601.0404152349.26dbc840@posting.google.com>,
and7@bigfoot.com (TekMan) wrote:

moonlightbamb@hotmail.com (moonlightbambi) wrote in message
news:<62f73ca0.0404120934.4b59797b@posting.google.com>...
There is a ground from the probe ( a wire and an alligator clip) which
is grounded to circuit ground.

I, unfortunately, don't have the tip accessories, ( I'm working on
it). The tip of the probe does have a cylindrical ground around the
pointy tip. since I'm going directly from the tips to the circuit,
that point in the grounds isn't grounded.

Are you implying that they need to be grounded independently?

thanks!!!!!
adam


the p6064 needs to be grounded seperately.
And do not drive out the common mode voltage range (appr. 4 Volt
without tips, higher with 10:1 or 100:1 divider probe tips).


hth,
Andreas

The probe will ring at a frequency determined by the parallel RC circuit
consisting of the probe capacitance and the inductance of the ground
reference path. To keep the ringing frequency high--so it will only
distort signals with very fast transitions--you want short ground leads.
That said, how short is short enough? A good rule of thumb is that a
ground lead provides about 25 nH of inductance per inch. Using the 5"
lead provided with the 6046 gives 125 nH. The input capacitance is 3
pf, which gives a resonant frequency of ~ 300 MHz. This is well above
the 100 MHz bandwidth of the probe. I think the lack if local grounding
of the probe tips is not likely to be the problem. Tektronix doesn't
seem to be much concerned with provisions for local grounding of the
tips either. I have the full accessory kit, and, with the exception of
a pair of coaxial probe tip jacks intended for circuit board mounting,
no local ground other than the ground lead, which comes in 5 and 12"
inversions, is provided.

I think the high frequency response of the two inputs is probably
unbalanced. The Tek procedure for checking high frequency CMRR
performance involves applying an identical 50 MHz signal to both probe
tips and ensuring the output is less than 0.1% of the input. They make
a special probe tip fixture for this. If you have a signal generator, I
think you could cobble something together with a 50 ohm feed-through
terminator and three goal post style BNC Ts (three Ys might be even
better). Connect the terminator to the generator followed by the base
of one of the Ts. Connect the other two Ts to the arms of the first one.
Turn these outer Ts so the open ports of each are aligned vertically.
Connect the two bottom ports together with a BNC jumper. Now, twist the
Ts so the jacks in the terminators are at the correct distance to accept
the tips of the 6046. Connect the ground lead from the probe to the
generator ground. Set the vertical deflection factor on the probe amp
to 1 mV and the generator for 2 V p-p. You should see a waveform of
less than two divisions on the scope.

If you try this and it fails, don't despair. The probe may be fixable
by calibration, which you could probably manage if you invest in a
manual.


Good luck!

Jon

Cheers,

 

[Ron Reaugh]

"Roger Johansson" <no-email@home.se> wrote in message

It doesn't hurt the computer and other devices if the voltage is raised a
thousand volts for a short moment, as long as all connections to it are
raised together. So the surge protector only has to keep all connections
at fairly the same voltage, even if they all are raised momentarily. What
really hurts the equipment is if one of the connections moves far away
from the other connections, because then there is a surge inside that
piece of equipment, burning some component to pieces.

That is why the extension with outlets protected by a surge protector
works. It creates a subsystem which is kept together at virtually the
same potential for all connections to that subsystem.

When a modem is hurt by the lightning it is because the mains connection
to it and the phone connection to it are pulled apart by thousands of
volts, and that creates a damaging surge inside the modem.

If both the mains and phone line connections to the modem first have to
pass through a protector box, where they are prevented from moving apart
too much, voltage-wise, the modem is protected.

You see there really are people around who understand surge protection.

 

[w_tom]

Electricity flows like an ocean wave? Now I know you have
absolutely no engineering knowledge. First electricity forms
a complete path from cloud to earth. Then as the current
increases within everything in that circuit, then something
eventually fails. Without the complete circuit, there can be
no electricity flow. That means first electricity flows
through everything in that circuit. Later something in that
circuit fail. Typically the entire surge is done in
microseconds. But the component can even take milliseconds to
fail. Electricity does not flow through devices like an ocean
wave - except where myths are promoted.

A simple principle is taught in Electromagnetic wave theory
- something taught to second year engineering students. Apply
electricity to a long wire. Where does voltage first appear?
Those who think of electricity in terms of ocean waves would
say voltage first appears where electricity connects to that
wire. They would be wrong because they did not learn
basic electrical principles. Instead, voltage first appears
at the far end of a wire. Again, a simple principle taught in
wave theory.

You are absolutely wrong that the charge, rolling down the
wire like an ocean wave, uses the first possibility to unload
itself. Wild speculation based upon junk science reasoning -
that electricity flows like ocean waves.

Classic modem damage is a circuit from cloud to earth. Only
after current flows through everything in that circuit, does
component failure occur. The component most often damaged by
an AC mains surge is in the DAA section - where phone wire
carries the current out of the modem to earth ground.

And again, if a surge is incoming on phone line, then why
does the always present phone line protector - installed free
by the telco - get ignored by the surge? Only if Roger did
not know the protector exists. Please explain why surges would
enter on a utility wire with 'whole house' protector AND not
enter on the utility wire that has no protector? Why would a
surge be created on a wire both lower and protected by the AC
mains wire? Clearly the incoming surge comes from the wire
highest on pole AND via wire that has no 'whole house'
protector - AC electric. Clearly, you do not even know that
phone line protector exists.

Furthermore, you are inventing new ideas on how electricity
works. Clearly you have no engineering training. Therefore
you are attacking my experience and credibility so that others
will be confused. You have no idea how electricity works.
Posting as if your entire electrical knowledge was in swapping
computer boards or because you sell consumer electronics with
highly profitable plug-in protectors. Again, where on that
long wire does a voltage first appear? At the end connected
to an electricity source (just like an ocean wave)? Or at the
far end of the wire. It is electricity - not an ocean wave.
Where does the voltage first appear?

Since voltage first appears at the far end of a wire, then
your wild speculation about what component is first damaged is
bogus. You believe the first component damaged is "a
component close to the input connection". That assumes
voltage first appears at the input connection. It does not.
According to your reasoning, the first component to be damaged
due to "power unloading itself" would be the *last*
component. The last component in that circuit would be the
first to see voltage from a surge using your reasoning.
Please do not invent electric concepts in a vacuum. Please
first learn how electricity works. Electricity first flows
through everything in that circuit. Only then does something
fail.

You are having difficulty even with concepts taught to first
year engineering students. That would explain why you hope a
plug-in protector is doing even what the manufacturer will not
claim. Its really a simple principle. A surge protector is
only as effective as its earth ground - which also explains
why the modem surge does not enter on phone line.

The original poster is encourages to place a 'whole house'
protector on the one utility that typically has no surge
protection - AC electric. Other wires such as phone line and
cable should already have protection, in part, because those
connections are required by National Electrical Code - for
other technical reasons.

Roger Johansson wrote:

w_tom <w_tom1@hotmail.com> wrote:
...
Many assume surges act like ocean waves. The surge destroys
the first component encountered? Of course not. Surge first
travels through everything in the circuit. Only then does
something fail.

I can take up one more point. The ideas you express above are
simply wrong, there is no scientific basis for that.

In fact, it is often a component close to the input connection
which fails, because the charge that comes rolling down the
wire uses the first possibility to unload itself to a potential
closer to earth level.

--
Roger J.

 

[P.T. Breuer]

w_tom <w_tom1@hotmail.com> wrote:

before you existed. It is quite likely that I had my first
engineering degree before you were walking. Polyphaser
equipment was defined for someone who does not even have first
year engineering education.

Never heard of it, and I have my PhD in electrical engineering from U.
Cam. Oh well.

Earthing a surge must be
accomplished with very short wire

He doesn't care, and neither do we, since as he pointed out, the
equipment doesn't care if it's earthed or not! That's why airplanes
keep right on flying when hit by all that electrickery ...

Peter

 

[P.T. Breuer]

w_tom <w_tom1@hotmail.com> wrote:

IOW the giant electrical wave appears just about equally on
everything in the circuit.

Sure it does, at different amplitudes! Simultaneously at high amplitude
near the strike, and low amplitude far away from the strike. As the
"ocean wave" rolls on, the amplitude rises farther away.

That is your delta wave.

Uh, "delta wave" is not a term known to me, but it's cute, and I'll
accept it!

Virtually everything is located in the same part of the wave
meaning there is near zero voltage difference.

This is simply not so - for current to flow at all there has to be a
difference of voltages. But if you are trying to say that
free-floating, unearthed (and well insulated from earth equipment is
safe because it experience zero voltage difference across it, I'd
agree! Let's all continue using airplanes.

Surges are done in microseconds.

Hey, let's not forget nanoseconds.

No, I can't take this very seriously.

Things go bang in
milliseconds. How do you explain the discrepancy?

Well, your point is what? That after a millisecond the first capacitor
across the rails blows apart? Personally, I wouldn't have given it more
than a few microseconds, but who's counting. Well, while it was taking
current it was keeping the voltage across it nicely down, in
conjunction with the huge voltage drop across the conductor (better
termed "resistor") leading to it. So it "protected" the rest of the
circuit for a bit, and then it popped, rather like the old waistcoat
button, straining the next one ...

Its quite
simple.

Oh ho ho!

Damage occurs to the circuit component that is
weakest and that absorbs excessive power.

Except that you have forgotten that it has to get there first. And to
do that it has to get past a whole lot of other things that might well
be stronger, but which have to last out until then ... it's an
interesting exercise to compute the power time integral across
differnet bits of circuit and see which hits the limit first. My money
would be on the first parallel component in line, most of the time.

Peter

 

[Ron Reaugh]

"w_tom" <w_tom1@hotmail.com> wrote in message
news:4151A9C4.FEC46E7F@hotmail.com...

Roger - chances are I was experimenting with this stuff
before you existed.

Possibly but NOT before ME, loonie.

 

[Noel Bachelor]

On or about 22 Sep 2004 01:54:14 GMT, Roger Johansson allegedly wrote:

I feel like I am discussing loudspeaker cables with an audio hi fidelity
enthusiast.

If you do a google search on his name, and you'll see he pops up like
clockwork whenever anyone mentions surge protectors, to spout his own
brand of 'myths'.

I thought he might quieten down a little after the hosing down he got on
rec.audio.pro late last year, but doesn't look like it.


Noel Bachelor noelbachelorAT(From:_domain)

 

[Roger Johansson]

see.my.sig@bigpond.com (Noel Bachelor) wrote:

I feel like I am discussing loudspeaker cables with an audio hi
fidelity enthusiast.

If you do a google search on his name, and you'll see he pops up like
clockwork whenever anyone mentions surge protectors, to spout his own
brand of 'myths'.

Yes, I soon realized what kind of fool I was talking to.
He gets boring after a few messages.


--
Roger J.

 

[Walter Harley]

"Michael" <maxel@berkeley.edu> wrote in message
news:ce5951b4.0409221343.dbd2157@posting.google.com...

I am performing a test to measure the impedance through electrode pads
placed on opposite parts of the human body. The protocol requires that
the measurement be made by maintaining an AC sine current of 200mArms,
sweeping the frequencies from 200kHz to 5MHz, and measuring the Vrms
between one electrode and a reference point on the body. The impedance
is to be calculated by dividing this voltage by the known 200mArms
current.

How do I sweep frequencies while maintaining a constant 200mArms
current using a HP 33120A (waveform generator w/ 0-15MHz freq and
0-10V peak to peak) or a HP 4192A (impedance analyzer w/ 0-15MHz freq
and -1V-+1V peak to peak)? Can I construct a circuit external to one
of these units and accomplish the 200mArms sweep? If not, what
lowest-cost set-up could?

See quasi-answer on sci.electronics.components. And, please learn to
cross-post, rather than posting multiple times, so that your messages will
be linked across the newsgroups. Thanks!

 

[Ron Reaugh]

"Kent Wills" <compuelf@gmail.com> wrote in message
news:9ri4l0ho4nhr3fnogsjckf7h0palco26ul@4ax.com...

I was just walking down the street, when someone handed me a piece of
paper. I thought it was something for a free meal at Popeye's
Chicken. Instead, I found that on 20 Sep 2004 19:37:36 -0700,
nospam256k@yahoo.com (nospam256K) wrote:

Here in New York City (Manhattan) where I live, I usually use a laptop
computer running on an AC adapter, and get online via a dial-up modem
(phone line plugged into computer's built-in modem).

When it's merely raining outside, it's usually of no concern to me.
But when there's lightning or thunder, I quickly get offline, turn off
the computer, and literally unplug the AC adapter from the outlet, and
unplug the phone line from the computer.

This is done to avoid the possibility of the AC adapter or the modem
suffering damage from a voltage spike carried through either the AC
power line or the phone line (because of a lightning strike).

Does all this sound sensible to you, or am I being
overly/unneccesarily cautious?

Odds are you would be safe, but it's certainly not dumb to
disconnect. It's far better to KNOW your computer is safe than to
take the risk and learn it's not.

After faithfully doing this chinese firedrill for many years now and never
having even heard of anyone personally who has gotten anything fried, I'm
wondering if/when the day will come when I say to myself...enough of this BS
and just party on during the storm<g>.

 

[Jim Yanik]

maxel@berkeley.edu (Michael) wrote in
news:ce5951b4.0409221343.dbd2157@posting.google.com:

I am performing a test to measure the impedance through electrode pads
placed on opposite parts of the human body. The protocol requires that
the measurement be made by maintaining an AC sine current of 200mArms,
sweeping the frequencies from 200kHz to 5MHz, and measuring the Vrms
between one electrode and a reference point on the body. The impedance
is to be calculated by dividing this voltage by the known 200mArms
current.

How do I sweep frequencies while maintaining a constant 200mArms
current using a HP 33120A (waveform generator w/ 0-15MHz freq and
0-10V peak to peak) or a HP 4192A (impedance analyzer w/ 0-15MHz freq
and -1V-+1V peak to peak)? Can I construct a circuit external to one
of these units and accomplish the 200mArms sweep? If not, what
lowest-cost set-up could?

I don't think your generator(s) will output 200ma into a load.
BTW,flatness of your generator probably depends on a 50 ohm load Z.

--
Jim Yanik
jyanik-at-kua.net

 

[Joe Davis]

After faithfully doing this chinese firedrill for many years now and never
having even heard of anyone personally who has gotten anything fried, I'm
wondering if/when the day will come when I say to myself...enough of this
BS
and just party on during the storm<g>.

I unplug my laptop from the AC and go on battery power. I'm connected to
the internet via my wireless router--if that takes a hit, all I lose is a
$75 box.

 

[Ed Price]

"Michael" <maxel@berkeley.edu> wrote in message
news:ce5951b4.0409221343.dbd2157@posting.google.com...

I am performing a test to measure the impedance through electrode pads
placed on opposite parts of the human body. The protocol requires that
the measurement be made by maintaining an AC sine current of 200mArms,
sweeping the frequencies from 200kHz to 5MHz, and measuring the Vrms
between one electrode and a reference point on the body. The impedance
is to be calculated by dividing this voltage by the known 200mArms
current.

How do I sweep frequencies while maintaining a constant 200mArms
current using a HP 33120A (waveform generator w/ 0-15MHz freq and
0-10V peak to peak) or a HP 4192A (impedance analyzer w/ 0-15MHz freq
and -1V-+1V peak to peak)? Can I construct a circuit external to one
of these units and accomplish the 200mArms sweep? If not, what
lowest-cost set-up could?

Before you get too deep figuring out "how" you do this, have you determined
"if" you may do this? I sure don't want anybody to put 200 milliamps through
me! Assuming a typical body resistance of about 1500 Ohms, doesn't that
imply about 60 Watts? True, I don't know what happens to body impedance as
you get into the low HF range, but maybe you should review the literature on
tissue heating one more time. Perhaps all your volunteers are already
cadavers. Or maybe you Berkeley guys don't know milliamps from microamps.

Ed
wb6wsn

 

[Mark]

"Ed Price" <edprice@cox.net> wrote in message
news:Lby4d.56609$9Y5.39735@fed1read02...

"Michael" <maxel@berkeley.edu> wrote in message
news:ce5951b4.0409221343.dbd2157@posting.google.com...
I am performing a test to measure the impedance through electrode pads
placed on opposite parts of the human body. The protocol requires that
the measurement be made by maintaining an AC sine current of 200mArms,
sweeping the frequencies from 200kHz to 5MHz, and measuring the Vrms
between one electrode and a reference point on the body. The impedance
is to be calculated by dividing this voltage by the known 200mArms
current.

How do I sweep frequencies while maintaining a constant 200mArms
current using a HP 33120A (waveform generator w/ 0-15MHz freq and
0-10V peak to peak) or a HP 4192A (impedance analyzer w/ 0-15MHz freq
and -1V-+1V peak to peak)? Can I construct a circuit external to one
of these units and accomplish the 200mArms sweep? If not, what
lowest-cost set-up could?


Before you get too deep figuring out "how" you do this, have you
determined
"if" you may do this? I sure don't want anybody to put 200 milliamps
through
me! Assuming a typical body resistance of about 1500 Ohms, doesn't that
imply about 60 Watts? True, I don't know what happens to body impedance as
you get into the low HF range, but maybe you should review the literature
on
tissue heating one more time. Perhaps all your volunteers are already
cadavers. Or maybe you Berkeley guys don't know milliamps from microamps.

Ed
wb6wsn

oh I hope it is microamps.... I've heard that 30millamps can kill!

 

[Walter Harley]

"Mark" <bigfathhairybiker@MAILhot(swapemround).com> wrote in message
news:4152f420$0$20246$ed9e5944@reading.news.pipex.net...

oh I hope it is microamps.... I've heard that 30millamps can kill!

Less than that can kill; but it has to actually get to the relevant muscles
(heart, diaphragm).

In this case, the *intent* of the OP was to use frequencies of 200kHz and
above. At those frequencies, the energy travels mainly on the surface of
the conductor, that is, on the surface of the body. Apparently, there is
not even any sensation of being shocked, even at fairly high currents.

If you do a bit of Googling for "high frequency current human body" (without
the quotes) you can learn more about this.

The key point, though, is that word "intent". As we all know, what actually
happens when you hit the switch on a piece of equipment is not always
exactly what we intended to happen. There is altogether too much risk that
an equipment fault or an operator error would result in substantial current
being delivered at lower, lethal, frequencies.

 

[w_tom]

In order to confuse issues, some will hype nonsense about
airplanes and then post insults as proof of his superiority.
We are discussing a particular type of surge where a cloud
conducts to earth. That is completely different from
transients that transverse airplanes. Others have had this
explained to them previously. To subvert the discussion, they
insult and then throw in totally irrelevant topics such as
airplanes.

Once ionization takes place, then capacitance of both sky
(air) and earth becomes irrelevant. One of the best
capacitors is air. However air gets converted into a good
conductor (plasma) due to something called breakdown voltage.
We require protection and only discuss surges after ionization
has occurred. Surge current (not surge voltage) becomes the
dominant variable after breakdown voltage is exceeded.
Capacitance is made irrelevant.

Surge protection is about earthing an ideal current source.
A surge is a current source after ionization has occurred.
Voltage will rise only as necessary to maintain that current.
This is the point when damage can occur and when protectors
must shunt that current to earth. Concepts that apply both to
properly earthed 'whole house' protectors AND to properly
earth Franklin air terminals (lightning rods). They both do
the same thing. Divert the surge current to earth ground so
that the surge will not find destructive paths through
household electronics or church steeples.

Suraj Singh wrote:

Surprised to see that no body talked about the capacitance of the
earth in this discussion.

Lightening do not bother to hit the airplane. Even if it does it do
not damage anything. Airplane capacitance is too small so a very
minute flow of charge can change its potential to match the cloud
potential. flow of minute change means little current ( micro amp)
which wont damage anything.

Imagine a situation where the plane has just taken off the ground,
lightening strikes its body and discharge to the earth through bottom
including pointed antennas in the wings; you can imagine the damage to
the circuit from where the antenna is connected.

As per the lightening is concerned one can not ignore earth if you are
close to it. You can dare to ignore if you are a much bigger mass
than earth.

You can raise the common mode potential of the system (say PC and
Modem), it helps but up to what extent? The charge on it will seek the
earth and if a short and quick high conducting path in not provided,
it may break down the air gap and discharge to the nearest path to
earth through the mouse wire.

Concept of GPR will provide much better protection if the whole house
is considered as a sub system. It will be economical too.
Power strips provide protection but for small surges only.

Best regards,
Suraj