How to perform 200kHz-5MHz sweep while maintaining 200mArms?

M

Michael

Guest
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?
 
"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?
Click to expand...

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!
 
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?
Click to expand...
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
 
"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?
Click to expand...

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
 
"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
Click to expand...

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