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Old 12-04-2018, 07:03 AM
dtryon dtryon is offline
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AC Isolation Monitor

Hey Folks,
I have tried to look but I can't find anything like I'm looking for. What I need is a circuit or kit or PC board design that will monitor AC line isolation. I need this to operate on a continuous basis. I want to monitor test equipment and or equipment under test so it remains isolated while being worked on. I would think someone has already designed something to do this function. I don't want to reinvent the wheel, lol. Can anyone help me with this problem?

Thanks,
Dennis
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Old 12-04-2018, 11:10 AM
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Electronic M Electronic M is offline
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With an isolation transformer with no load or as long as the load is not connected to AC powered test equipment a voltage measurements between primary and secondary will suffice. 0v equals isolated. However that measurement will reduce isolation creating a 1M ohm leakage... that test will also likely fail as soon as the isolated radio is connected to AC powered test equipment.

In practice checking isolation before use on a radio daily or however often you work should be sufficient.
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Old 12-04-2018, 12:32 PM
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N2IXK N2IXK is offline
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Line isolation monitors are certainly available, but are you sure you want to pay for one? The primary application for them that I am aware of is for monitoring isolated circuits in operating rooms for hospitals. As you can imagine, they come with that "specialized, critical life support equipment" kind of price tag:

https://www.grainger.com/product/SCH...-Monitor-7DE30
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Old 12-04-2018, 03:06 PM
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benman94 benman94 is offline
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The primary usage is in medical equipment, not terribly sure why you would need or want one for old TVs and radios...

MEG and EEG equipment is commonly connected to line-isolating equipment, and there are numerous fail-safes in place within the circuitry of equipment itself that keep an EEG from becoming an unexpected trip to the electric chair. The risk with MEG is minimal as you're essentially wearing an enormous dewar on your head and there's no electrical contact to begin with. EEG there's a real risk if strict isolation of the leads and amplifiers from the power supply isn't maintained at all times. The same goes for EKG equipment...

It also helps keep the noise and BS from Edison out of the power supply, which is a great advantage when trying to amplify such incredibly small signals.
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Old 12-04-2018, 03:25 PM
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Unless you have a heart condition failure of the isolation on your repair bench should only result in a strange tingling, mild pain that subsides in a few seconds of letting go of equipment, and the release of some foul language... assuming safe bench practice. Test equipment.damage.is possible too.

Safe bench practice is only touching one potentially conductive object at a time (some recommend keeping one hand in your back pocket). Remember on a hot chassis TV or radio that uses a double you can have around 320VDC at lethal current levels....An isolation transformer will NOT save or even help you if one hand is touching B+ and the other is touching B-....no amount of equipment can cover for bad bench practice.
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Old 12-05-2018, 12:37 PM
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Have you considered an inexpensive ground fault circuit interrupter?

https://www.amazon.com/s/ref=nb_sb_s...d=83BKEWGQMK9Q

not affiliated,
jr
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