Hi Mick:
In 1961, James J. Gibson published a paper entitled “The contribution of
experimental psychology to the formulation of the problem of safety: a brief
for basic research.” This paper reported his studies of injury causation in
automobile accidents:
“Injuries to a living organism can be produced only by some energy interchange.
Consequently, a most effective way of classifying sources of injury is
according to the forms of physical energy involved. The analysis can thus be
exhaustive and conceptually clear. Physical energy is either mechanical,
thermal, radiant, chemical, or electrical.”
In other words, Joules transferred to (or from) a body cause injury. Actually,
Joules per second. In an automobile accident, a lot of kinetic energy can be
transferred to a body in a short time.
Wikipedia gives some practical examples of one Joule of energy:
https://en.wikipedia.org/wiki/Joule
Gibson’s thesis is the basis for IEC 62368.
So, we have ES, electrical energy source, MS, mechanical (kinetic) energy
source, PS, power source (fire), RS, radiation energy source, and TS, thermal
energy source.
For ES, a watt-second is a Joule. E x I is a watt. The standard limits both E
and I individually (but we always have both and therefore have watts
transferred to the body). Time is forever. For higher voltages and currents,
we limit the time, such as a GFCI (but not in IEC 62368).
All of the other energy sources can be similarly shown to be based on Joules
per second. For the most part, the standard assumes the energy available for
transfer to the body is steady state.
Note that the body can safely absorb energy when Joules/second is small. The
body has several thresholds for energy which depend on the energy format. In
IEC 62368, three thresholds for each energy format are given: detectable,
painful, and injurious, hence ES1, ES2, and ES3, etc.
The requirements are based on the body response to a parameter, which is why
there is no reference to TNV or similar parameter.
Hope this helps.
Best regards,
Rich
From: Mick Maytum <mjmay...@gmail.com>
Sent: Thursday, March 14, 2019 10:09 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] classification of the output
Pete,
Glad to see your thoughts agree with mine. With large amplitude voltage
pulses there must be some EMC considerations that come into play for equipment
EMC compliance.
I really wish that some alternative abbreviation had been created instead of
ES. Many engineers would be looking for a Joule parameter for an energy source,
yet Joules don't get a direct mention in the IEC 62368-1 body text description
(Why no entry in definitions?). Expressing ES as a voltage, current and charged
capacitance (no inductive current) makes it multi-option classification.
Further when it comes to telecommunications TNV circuits, those are classified
by DC working voltage alone.
Thus they are ES1 or ES2 DC working voltage circuits not simply ES1 or ES2
circuits as that would drag all the other ES factors in.
-
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