Kris, This seems to be a troubling point for a number of folks.
The temperature limits in 62368-1 are based upon the
available scientific data (which is what a Hazard Based standard is all
about). This data is only available for measurements taken at 25C, a common
lab temperature. The skin response is non-linear with temperature so it is
not appropriate to adjust the results based upon evaluation at another
ambient test temperature.
The proper evaluation is to test the product at 25C and
confirm that it meets the limit in the table for the expected contact time
and material.
IEC TC 108 agonized over this quite a bit and have repeatedly
had the same conversation downstream in their sessions; it seems to be a
hard concept to grasp. Recognize that the IEC recognized this approach as
the proper one and issued Guide 117 based upon the same reasoning to be
applied to all touchable surfaces.
Any measurements made at any other ambient temperature are
interesting but only should be used for any other considerations that might
be of interest to the investigator.
:>) br, Pete
Peter E Perkins, PE
Principal Product Safety & Regulatory Affairs Consultant
PO Box 1067
Albany, ORe 97321-0413
503/452-1201
IEEE Life Fellow
<mailto:[email protected]> [email protected]
From: Carpentier Kristiaan <[email protected]>
Sent: Monday, January 13, 2020 3:50 AM
To: [email protected]
Subject: [PSES] Touch temperature levels
Hi group,
IEC62368-1 Table 38 defines touch temperature limits. Are these values
absolute values nomatter which ambient?
It seems some safety laboratories consider these values relative to 25C,
thus allowing a recalculation to higher touch temperatures at higher Tma,
other labs consider as absolute values.
Examples: TS1 limit on plastic/rubber is 77C.
Labs that stick to absolute values have a limit of 77C at 25C and also at
Tma of 45C.
Labs that allow recalculation allow 97C for Tma of 45C, which is well in
line with the 95C value of IEC60950-1.
Any explanatory guidance documents available?
Regards,
Kris
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