Janky ESD Immunity Testing with the Zerostat 3?

[CoolNamesAllTaken]

I was watching a video last night that happened to mention using a Zerostat 3 ion gun and copper foil tape spark gap for ESD immunity testing: https://youtu.be/qQpPxz0X8jg?t=85

Does anyone know how this process works? It seems like an intriguing alternative to shelling out for a real ESD gun rental (~$500 for a basic rental seems to be in the right ballpark), since the Zerostat 3 is used for cleaning records and retails for under $100.

I guess the other tricky part is--would there be any way to measure or control the test and make it repeatable? I know that real ESD simulators can charge a capacitance for the simulated human body or machine model to various voltage levels. If I were to charge up a spark gap jig with the Zerostat 3 and zap one of my circuits, would there be a good way to measure the voltage accumulated across the spark gap before discharge?

[helius]

The breakdown voltage of a spark air gap is generally estimated at 3 kV/mm. It will vary depending on atmospheric humidity and temperature. If you need a more precise reading, you would need to use very high impedance instruments, since any lower-impedance connection will drain away any charge. Even high-voltage probes with their 1 gigaohm impedance are probably insufficient.

The highest impedance voltage probe is a non-contact electrostatic locator. If your spark gap copper strip is sufficiently large, you can aim the locator at it and read the voltage without contacting it.

[CoolNamesAllTaken]

Thank you for the fast reply! I've acquired a non-contact static field meter and a ZeroStat 3, and will attempt some experiments with copper foil tape to see if I can create a consistent spark gap.

For calibrating a spark gap, would this be a reasonable procedure?
1) Build copper foil tape spark gap with the 3kV/mm estimate.
2) Hold one end of the spark gap, and spray positive ions onto the other end. Check charge buildup on either end of the spark gap using the static charge locator.
3) Continue alternating charge spray and voltage checking until the gap arcs over. Hopefully the final difference in static charge potential across the gap lines up with the rough 3kV/mm assumption.

[helius]

Yes, that's a reasonable procedure. Some points might need attention: When holding the Zerostat, does it charge your body in the process of generating ions? Maybe you need to wear a wrist strap. The Zerostat has two points, presumably one emits positive ions while the other emits negative ions. Does this direction reverse when the handle is released? A static locator needs to be zeroed while pointing at a neutral field, such as towards the middle of the room. Take note if its reading is affected by the Zerostat gun.

The breakdown voltage of your spark gap will be roughly constant if the temperature and humidity are controlled. Over time it will change as the copper oxidizes or spalls off during sparks, attracts soot (carbon) or other contaminants from the air. So you may want to recalibrate after every hundred or so sparks or after a month or so in storage.

[CoolNamesAllTaken]

Thank you for the great advice! I'll use a wrist strap to stay neutrally charged when using the Zerostat. I am not sure where the negative ions go when pulling the handle, but I do know that the direction of the handle determines the polarity of the ions produced. Instructions often say to pull the handle slowly to add positive charge, and release the handle slowly to add negative charge (or maybe it's the other way around).

I haven't seen much info about this on the web, so I'll be sure to share my results here as I figure things out!

[GLouie]

I have also heard of using a handheld gas cooking igniter (BBQ sparker). It apparently generates a reliable spark, but not meant to spew ions like a Zerostat.