How to isolate my circuit from the sensor wire?

[Inkwaterman]

ESD problem

Hi to everybody!

I have a problem.

I use an analog to digital converter for convert a signal from a sensor.

This sensor is far from the ADC and I must use 4 long wire inside a metallic shield for the connection.

Sometime an electronic discharge "hit" this metallic shield and my circuit go down.

I must isolate my circuit from the sensor wire.



How I can do ?



I need also to feed the sensor.



In total I have 4 wire:

2 wire sensor's signal

1 wire for +5V

1 wire for GND

 

[sefton]

Re: ESD problem

What do you mean by "my circuit go down" ?

If your signal from the sensor is not changing too quickly, you can isolate it with a voltage to frequency converter -> opto isolator-> frequency to voltage converter.
You would also need an isolated DC/DC converter for the 5V supply and of course spike protection, such as a transzorb. Perhaps you can just use spike protection only.

 

[Inkwaterman]

Re: ESD problem

>What do you mean by "my circuit go down" ?

I wanted to say: it stops to work.
It's strange because it seem that some voltage regulator (78XX type) of my circuit start to work badly, and the only remedy is switch off the power.

>If your signal from the sensor is not changing too quickly, you can isolate it with a >voltage to frequency converter -> opto isolator-> frequency to voltage converter.
>You would also need an isolated DC/DC converter for the 5V supply and of >course spike protection, such as a transzorb. Perhaps you can just use spike >protection only.

The frequency conversion it's a good idea , but in my case it's not possibile put an IC near the sensor.

 

[DoctorProf]

Re: ESD problem

It sounds like you may be getting non-destructive latch-up. The charge from the cable injects charge into your circuit causing an SCR type action.

You could put some voltage suppression (MOV, Zener, etc) to clamp the voltage to your power supply level. There are several external protection circuits that are available on the market.

Check out http://www.littlefuse.com. They are a company that sells suppression circuits (MOV, Zener, ESD Clamps) that are added to a PCB.

Dr.Prof