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Technical Tidbit - September 2014
Human Metal Model ESD Compared to Direct Skin Discharge (Human Body Model) ESD
Revisited in Video Format)

Test Setup for HMM ESD

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.

Figure 2.
HMM/HBM Comparison Video

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:
Equipment used in this Technical Tidbit:

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