Ac milli-voltmeter issue

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arvinfx

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Hi,

I am making a protection circuit for a "relay-contacts" that works as a ac mili-voltmeter .

for example if there is 0.6Vac on the relay-contacts so I need a signal . But problem is the contacts have 220Vac and I don't know where to connect the ground for opamp side!

 
I think you want to measure the "closed " voltage across the contacts. But if a contact opens while you are measuring it the meter circuit will die.
 
I think you want to measure the "closed " voltage across the contacts. But if a contact opens while you are measuring it the meter circuit will die.

It will worse when an inductive load connected on the relay! A huge spark is second issue !

And no I want to measure the resistor on 2 contacts, not closed contacts
 
You do not seem to have any means to control the power supply voltage to the op amps.
The current to the op amp supply is controled by the reactance of C5. I would normally expect to see a zener diode across the supply lines to control the voltage.
You say "I want to measure the resistor on 2 contacts, not closed contacts". You do not have any resistor connected to the relay contacts.
I am guessing that you want the relay to be energised only when the mains voltage is between two specified voltages.
In other words if the voltage is too high or too low you do not want the relay to be energised.
Is this guess correct.

Les.
 
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