EMI metrics

[bwilson4web]

Hi,

Over in PriusChat we have periodic visits by those who claim to suffer from Prius EMI:
"https://en.wikipedia.org/wiki/Electromagnetic_hypersensitivity"

This is usually met with counter facts and data and the original posters wander off. But last week, I got a Gulf Coast Data Concepts data recorder: http://www.gcdataconcepts.com/ham.html

• 3-axis accelerometer
• 3-axis gyroscope
• 3-axis magnetic field

Over Christmas, I've been working on software to extract the data in a spreadsheet friendly form. Then I realized the magnetic sensors could perform a quick if rough EMI study. Magnetic sensors sensitive enough to read the earths magnetic field would be perfect for sampling EMI magnetic fields.

The GCDC recorder was taped to a console in the cabin under the center arm rest. Then I drove to a favorite benchmark route:

For these tests, I entered from the south road, took a left, set the cruise control to 25 mph, and did three laps in a clockwise direction.

I loaded the data into a spreadsheet, normalized the raw data, the instrument counters, around the average for each axis and generated these graphs:

• The data points are in the direction of travel, a tangent vector around the loop. So the North vector value occurs on the far left, West end, of the loop. If you mentally rotate the graphs 90 degrees to the left, the blue-line values would overlay the loop.
• There is EMI at levels ~5-10 times smaller than the earth magnetic field.
• The EMI bursts occur when either the Prius or the BMW i3-REx are under load or regeneration. The magnitudes are very low compared to the variation in earth magnetic field.
• The Mz variation is a measure of the road 'crown', the slope needed to let rain water run off into the gutters. It does not need to be rotated since it is normal to the direction of travel.

I was surprised that the steel body, Prius, and carbon-fiber body BMW i3-REx appear to have nearly identical earth magnetic field values. I would have expected the Prius body to attenuate it. Both tests were at night and I can not rule out stray fields from lights or other sources. But the EMI bursts were consistent with vehicle power generation and regeneration due to the grades.

EMI is real but the levels are very low. There may be people sensitive to these levels but I suspect there may be different reasons: seats, cabin material, or other. For example, I have a needle phobia that puts me into shock anytime I get an injection.

When a student under supervision of a teaching nurse was practicing putting in an IV while I was 'instrumented' in a heart ward several years ago . . . suddenly we had three staff from the monitoring station come in to see why I was going into shock. <grins> So I'm sympathetic to those claiming EMI associated disorders knowing full well it is easier to suggest they get rid of their Prius than the harder problem of resolving their phobia.

Bob Wilson

 

[jadnashuanh]

The i3 has a much more robust motor than the Prius, so the current required under high power situations could be substantially higher. It depends somewhat on how the cabling is routed and where the current using devices are relative to the passenger compartment as the strength will vary quite a bit as the distance increases.