Hello guys, i need your help to understand how the ESD monitors do work, i mean how do they detect if an operator is wearing or not the ESD wrist strap.
I'd be very grateful if someone knows the answer.
Thank you in advance.

 

Few ways of going about it

Capacitance - measuring capacitance of a person relative to ground because a person is conductive

Impedance - tiny current and measuring phase angle between I and e.

Resistance - this would require a dual strap to measure the resistance of skin vs open.

 

Hello guys, i need your help to understand how the ESD monitors do work, i mean how do they detect if an operator is wearing or not the ESD wrist strap.
I'd be very grateful if someone knows the answer.
Thank you in advance.

All of the ones I worked with for testing ESD stations and those who worked at them simply tested resistance. A simple comparator circuit with a few LEDs and checking those units was just a simple matter of a few precision resistors.

Ron

 

All of the ones I worked with for testing ESD stations and those who worked at them simply tested resistance. A simple comparator circuit with a few LEDs and checking those units was just a simple matter of a few precision resistors.

Ron

What i dont understand is how could you measure anything when you only have one wire feed back from the wrist band, can you please suggest an explanatory circuit to demonstrate the process ?

 

Few ways of going about it

Capacitance - measuring capacitance of a person relative to ground because a person is conductive

Impedance - tiny current and measuring phase angle between I and e.

Resistance - this would require a dual strap to measure the resistance of skin vs open.

I like the idea of measuring the capacitance of a person since i am dealing with 1 wired wrist bands, but how would you do it? should you run a current through the person to the ground or what? if you suggest a circuit that would help a alot. Thank you.

 

What i dont understand is how could you measure anything when you only have one wire feed back from the wrist band, can you please suggest an explanatory circuit to demonstrate the process ?

The way they work is pretty simple. The user wears a wrist strap which has a metal tab and the strap is made of material with conductive fibers. While often called a ground strap that is not really true. Wrist straps have a resistor in the cord and the cord connects to a grounding tab. Let's take a look at a wrist strap tester and they are all about the same.



The user places their wrist strap on their wrist and plugs the cord into the Yellow Banana Jack. The user then pushes the metallic Push to Test button. Just about all strap testers work the same, some fancier than others. The path is between the yellow jack and the strap through the user to the metal button. The LEDs are illuminated depending on the resistance total measured. A Google of "esd wrist strap tester circuit diagram" should give plenty of examples. A further Google of ESD Specifications will bring up a countless series of specifications quite literally from floor to ceiling and everything in between. Obviously if a user is not wearing a strap which is in spec or no strap there will be a high fail on the testing.

It has been decades since my involvement with ESD but as to a normal ! Meg strap and user < 750 K Ohm = Low fail. OK Pass range is 750K to 10 Meg Ohm and above 10 Meg is a high fail I am sure it is in a specification somewhere.

Ron

 

The way they work is pretty simple. The user wears a wrist strap which has a metal tab and the strap is made of material with conductive fibers. While often called a ground strap that is not really true. Wrist straps have a resistor in the cord and the cord connects to a grounding tab. Let's take a look at a wrist strap tester and they are all about the same.

View attachment 201219

The user places their wrist strap on their wrist and plugs the cord into the Yellow Banana Jack. The user then pushes the metallic Push to Test button. Just about all strap testers work the same, some fancier than others. The path is between the yellow jack and the strap through the user to the metal button. The LEDs are illuminated depending on the resistance total measured. A Google of "esd wrist strap tester circuit diagram" should give plenty of examples. A further Google of ESD Specifications will bring up a countless series of specifications quite literally from floor to ceiling and everything in between. Obviously if a user is not wearing a strap which is in spec or no strap there will be a high fail on the testing.

It has been decades since my involvement with ESD but as to a normal ! Meg strap and user < 750 K Ohm = Low fail. OK Pass range is 750K to 10 Meg Ohm and above 10 Meg is a high fail I am sure it is in a specification somewhere.

Ron

I really appreciate the time you took to write this very detailed and informative article. It has been very helpful thank you very much.

 

My pleasure.

Ron