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The above is just a basic EEG circuit for sake of illustration. Suppose you are using it and the neutral electrode which is connected to the AD620 reference is connected to your skin. And you put an antistatic ground wrist band in other wrist that is connected to the power line ground. Is there any ground fault that can damage the AD620 (or others) reference pin? Ground fault for example lightning hitting the ground or some potential in the ground which can conduct through you and damage the AD620 reference pin by raising the voltage to higher than its tolerance?

 

I have twice experienced direct lightning strikes to my radio tower, which transferred to our house. Lightning will go wherever it chooses. Even with only one ohm between tower top and bottom, 10,000 amps develops 10,000 volts to go where it will.
For the EEG circuit shown, there is no functional benefit from attaching the patient reference to the mains safety ground. Consider that the patient reference connection is to control the common mode voltages relative to the two patient sensing connections. How can that function be improved by connection to the outside world???

 

I have twice experienced direct lightning strikes to my radio tower, which transferred to our house. Lightning will go wherever it chooses. Even with only one ohm between tower top and bottom, 10,000 amps develops 10,00 volts to go where it will.
For the EEG circuit shown, there is no functional benefit from attaching the patient reference to the mains safety ground. Consider that the patient reference connection is to control the common mode voltages relative to the two patient sensing connections. How can that function be improved by connection to the outside world???

The antistatic wrist band connected to power line ground is to avoid static damaging the inputs of the amplifier.

 

The only need for a wristband is when you are working on a static sensitive circuit. If you have all if the grounds connected properly, that’s all you need, the wristband is only useful when you have your hands in the circuit. I don’t use wristbands though I once installed them on a factory floor.

ESD damage is rare. I’ve only damaged one chip with ESD in
more than 50 years of working with CMOS (and that was while trying to induce an ESD failure).

Use your native intelligence and touch ground before touching the workpiece (the same ground to which the workpiece is connected, and for the most part, keep your hands off of the circuit as much as possible, and make sure all grounds are connected to each other.

“Ground” is not magic-just a common connection point in the circuit.

 

The only need for a wristband is when you are working on a static sensitive circuit. If you have all if the grounds connected properly, that’s all you need, the wristband is only useful when you have your hands in the circuit. I don’t use wristbands though I once installed them on a factory floor.

ESD damage is rare. I’ve only damaged one chip with ESD in
more than 50 years of working with CMOS (and that was while trying to induce an ESD failure).

Use your native intelligence and touch ground before touching the workpiece (the same ground to which the workpiece is connected, and for the most part, keep your hands off of the circuit as much as possible, and make sure all grounds are connected to each other.

“Ground” is not magic-just a common connection point in the circuit.

Have you guys forgotten that in EEG. The differential inputs In+ and In- are connected to your skin. So walking on dry floor..wont your body pick up static enough to damage the 2 inputs?

 

Here is the point



To avoid damage to the inputs. I must wear an antistatic wrist band connected to power line ground. My question is what if the ground develops potential..can it damage the device inputs?

Note in other devices. Its assembled with no exposed pins..except an EEG where the electrodes are the exposed pins of the ic.

 

Consider that the purposes of the wrist band in the two applications are quite different. And that the main purpose of that third pin ground is even farther different.

 

So please tell me. If the EEG inputs are so ESD sensitive, then wearing antistatic wrist bands with 1 MegaOhm inside it during EEG use is ok? no chance the wrist band can be affected by the many faults current moving in the earth and affecting me or damaging the EEG unit?