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Just a question with regards to galvanic isolation. I don't understand what it is, is it a some galvanised metal put in between the network, or is it a resistor network? I am trying to eliminate an AC voltage in my RS485 line.

http://www.rs485.com/pfaq.html#GalvanicAnchor

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Galvonic Isolation - forced isolation between the two circuitry, Transfer of energy between the two circuitry without direct flow of current.
eg. Opto coupler , Isolation transformer

Isolating the primary and secondary circuits for acheiving common mode attenuation.

Secondary circuit in no way will be affected by the implications created on the primary circuits by the external factors

It means an isolation between 2 circuits, i.e. no metal conduction between those circuits. Transfer will then take place for instance optical or by induction (magnetic).

Think of your mains transformer, if you take an Ohmmeter, and try to measure the resistance between the primary and secundary windings, you find a very high to indefinite value, if this is a good transformer though.

So isolation is the word, Galvano is one of the guys in the 18th century whom did a lot of research in that area, like Ohm and Volta.

Hope this simple explanation will help you.

Henri

It's not too complicated. Galvanic means "related to direct-current electricity" or DC. Galvanic Isolation says that the circuit is separated from the signal source (or sink) in such a way that DC current cannot bridge the connection. There are two generally accepted methods for galvanic isolation: use of transformers or use of optical isolators. Both allow the AC component of a signal to pass, but not the DC component.

Your network signal appears as AC on RS 485. I believe you don't want to use Galvanic Isolation. You need to pass low voltage AC but block high voltage AC. Intrinsic safety barriers for RS485 will do this. They use a Zener diode that will shunt any high AC voltages to ground, should they occur, along with the signal. If you always have high voltage AC present, you have more problems than we can
discuss here.

Dick Caro
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First, "isolation" refers to two circuits which are not connected electrically, with no conductivity between them. Now the problem arises when we must use information from one circuit in the other while maintaining the isolation. One way is by using light produced in one circuit and sensed in the other; thus you will find the phrase "optical isolation". Another way is to pass the two circuits through the primary and secondary of a transformer; this is "galvanic" isolation, so "galvanic" just refers to the specific means of transmitting information between electrically independent circuits.

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Steve Myres, PE
Automation Solutions
(480) 813-1145

Is GI an effective method of control for Electro Static Discharge?

Not by itself, no. In fact, isolating circuits can make them more vulnerable to ESD in certain circumstances. Grounding, shielding and dissipation are tools for ESD control. And there are few simple answers.

Regards
cww

Galvanic isolation means that there is not conductive (usually metallic) connection between two circuits. It is usually achieved by optocouplers. In your case, the two sites connected by the RS485 link have different (and
probably bad) grounding.
Meir