[EE] ESD Test Fixture Calibration, Build and Calibrate Magnetic Current Sense Probe?

[Jason White]

Hello everyone,

For work I have build a conducted ESD test circuit to test using human body
model at 4kV. (from MIL-STD-883 method 3015.9) For those interested I have
attached a schematic of the circuit.

The specification calls out a required levels and rise times for the
current waveform generated by the ESD tester (partial graph attached).
Furthermore it specifies that a 350MHz scope and magnetic current probe be
used to calibrate the process.

I do not have a scope of sufficient bandwidth nor do I have a current
probe. Nevertheless, I would like to attempt to fabricate and calibrate
small magnetic current probe (transformer) for use with the fixture.

Here is the idea: a 0.1-3.0 amp (AC/transient) current would pass through a
single HV insulated wire. Wrapped around the wire would be N number of
turns of magnetic pickup wire wrapped at a diameter D. An oscilloscope
would capture the induced potential in the pickup coil.

My initial google search didn't show too much for my application. Any
suggestions for suitable values of N and D?

Presumably N should be "high" and D should be as "small as possible".

[Sean Breheny]

I would strongly suggest using a proper current transformer. Suitable ones
are made by a number of companies such as Pearson and LEM.

They can often be found on eBay for not too much money ($100 is quite
likely, maybe less)

You are on the right track with your idea of how to make one except that
some type of core is really important to get accuracy. Otherwise the exact
alignment between the primary and secondary will change the calibration
significantly.

You also likely want an electrostatic shield between the primary and
secondary to prevent capacitive coupling due to the high dV/dt during the
pulse. This is all taken care of in a purpose-made unit.

How are you going to deal with the fact that you don't have a scope of
sufficient bandwidth?

Sean


On Thu, Aug 23, 2018 at 8:46 AM, Jason White <

Post by Jason White
Hello everyone,
For work I have build a conducted ESD test circuit to test using human body
model at 4kV. (from MIL-STD-883 method 3015.9) For those interested I have
attached a schematic of the circuit.
The specification calls out a required levels and rise times for the
current waveform generated by the ESD tester (partial graph attached).
Furthermore it specifies that a 350MHz scope and magnetic current probe be
used to calibrate the process.
I do not have a scope of sufficient bandwidth nor do I have a current
probe. Nevertheless, I would like to attempt to fabricate and calibrate
small magnetic current probe (transformer) for use with the fixture.
Here is the idea: a 0.1-3.0 amp (AC/transient) current would pass through a
single HV insulated wire. Wrapped around the wire would be N number of
turns of magnetic pickup wire wrapped at a diameter D. An oscilloscope
would capture the induced potential in the pickup coil.
My initial google search didn't show too much for my application. Any
suggestions for suitable values of N and D?
Presumably N should be "high" and D should be as "small as possible".
--
Jason White
--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist