PSNet
MV asked re: a device which generates 12V dc between a users hand and
other parts of their body; wot is the body resistance and wot current can be
expected to flow, wot risks, etc...
IEC 479 'Effects of current passing thru the human body' gives the basis
for answering these technical questions. Most of the data available focuses on
AC currents from systems at mains voltages, but the discussion is extended to
low voltages including DC systems.
The 120/220V impedance of the body is in the range of 1k to 1.5K ohms.
As the voltage is reduced, the impedance increases and at the low voltage of 10V
the impedance would be above 2K, maybe 3.5K or so. AC sources have the
advantage, of course, that they can capacitively couple across the relatively
high resistance of the skin to the low resistance of the inner salt bag of the
body.
The body can handle higher levels of DC current than AC for the same
body
response, something on the order of 4 times the current. So, for instance,
where a 0.5mA AC reaction current is found, 2mA DC current would provide a
similar response.
For sustained currents, usually no harmful physiological effects are
found at currents below 10mA AC/40mA DC.
For the example being discussed, the expected current would be in the
range of 4mA to 6mA. This is above the reaction levels of 0.5mA AC/2mA DC but
below the harmful levels mentioned above.
Medical devices are regulated in most developed countries - including
Europe and North America. The technical requirements are laid out in IEC 601 -
or it's equivalent European and American variations.
Hope this helps.
:>) br, Pete Perkins
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Peter E Perkins
Product Safety Consultant
Tigard, ORe 97281-3427 USA
+1/503/452-1201 fone/fax
[email protected] email
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