High
Frequency Measurements
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Douglas
C. Smith
Technical
Tidbit - September 2014 Human Metal Model ESD Compared to Direct Skin Discharge (Human Body Model) ESD
(Revisited in Video Format)
Figure 1. Test Setup for Illustrating Human Metal Model ESD
Abstract: There are two models
of human generated ESD that are widely used. These model a human
holding a piece of metal (HMM) and a direct discharge from human skin
(HBM). Using radiated induction into a shorted scope probe as a measure
of the severity of an ESD event, these two types of human discharge are
compared on live video. It is shown that even a small piece of metal
being held in a hand can significantly increase the intensity of an ESD
event.
HMM ESD is of concern for its effect on electronic systems and is
described in IEC 61000-4-2 whereas HBM ESD is of concern for damaging
electronic devices as they are handled. Click here for a discussion of HBM on Wikipedia.
Using the induced voltage into a shorted scope probe from the radiated
EMI of a nearby ESD event, we can judge the severity of the ESD event .
The video linked from Figure 2 below compares the severity of the
Human Metal Model (discharge from a piece of metal held in a hand to
the Human Body Model (direct discharge from human skin) from the point
of view of radiated fields. The amount of voltage induced into the
probe is a good indication of the interference potential to electronic
equipment. You will be surprised at the magnitude of the HMM discharge
and its comparison to an HBM discharge.
The conclusion and data are similar to my April 2013 Technical Tidbit,
but the video format brings out the differences and the superimposed
waveforms in the video give an idea about the repeatability of these
events.
You are welcome to copy this video, use it in training, or distribute it as long as it is unedited and shown it its entirety.
Summary: There is
a large difference in the severity of radiated fields from HMM and HBM
ESD events and therefore in the events themselves. HBM is much less of a threat than HMM. This difference has implications to electronic equipment used in environments that are not controlled for ESD.
Technical Tidbit on this site related to this article:
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