1-Wire mains detection

Is there a 1-Wire(*) device that can detect the presence of mains? I suspect that the DS2413 might do it but ideally I'd like it to be galvanicly isolated so there is no chance of mains getting where it shouldn't and frying things.
The application is to monitor the various pumps and demands on the heating system here in conjunction with a scattering of 1-Wire temperature sensors.
(*) "1-Wire" as in using the same system as the cheap temperature sensors you can get from Dallas/Maxim.
--
Cheers
Dave.




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wrote:

Glue one of the temperature sensors you are already using to a suitably insulated resistor.
John
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Dave Liquorice wrote:

Volts or amps?
Only, volts on mains wiring is really hard to detect reliably with a high resistance isolation as it is so easy to pick up stray voltages.
How about something really simple, like a mains powered relay, an opto- isolator, or a home brew optoisolator using a photo-device pointing at a fully sealed mains LED unit?
--
Tim Watts

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On Fri, 06 Jan 2012 17:22:47 +0000, Tim Watts wrote:

Presence ie is something switched on? Loads are around 50W for circulation pumps or oil boiler. I've been half looking at hall effect switches to feed into a DS2413 1-Wire dual channel PIO device. But I haven't a clue about the field strengths that hall effect switches need or those that you'll find around a mains cable carrying 200mA or so.

I have a load of relays that could be liberated from the old control box but that just seems a bit over kill and "old fashioned" but does solve the isolation side. I can't help feeling that there must be something from the process control area for this but perhaps they don't come cheap...

Mains LED indiactor, opto switch into a DS2413 that's another way. Might be a fair bit of messing about with heatshrink to make light tight units though.
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Cheers
Dave.




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On Fri, 06 Jan 2012 21:42:06 +0000, Dave Liquorice wrote:
<snip>

There are voltage and current sensors available, but you probably don't want to pay the cost - especially for the current sensors! There are also little hall effect sensors at a more reasonable price. The problem is that they give an AC output around zero (and need a negative supply). I once used a system of connecting an opto-isolator & resistor to watch the voltage across series diodes (actually a bridge rec with + and - shorted), but you get a 1.2v or so drop and a pulsating DC signal to deal with. A relay to watch just the voltage is a lot easier!
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Mick (Working in a M$-free zone!)
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Dave Liquorice wrote:

Looks like a very handy device, that...
The only way I can think of doing a reliable non contact volt-detection is to do something like slip the conductor through a small bit of brass tube (the detector), then oversleeve that with some plastic, then oversleeve again with bigger brass tube which is earthed to provide some local shielding from other stuff - but then you'd probably need to amplify the signal which leads to a problem of power for the amp circuit.
Unless the DS2413 was sensitive enough to cope directly.
It mentions it has 1M input impedance and a max voltage of 28V on the IO pins - wonder if a signal diode->tiny capacitor+clamp zener+high-ohms bleed resistor could clean up the induced mains hum on the pickup (ie turn it into a DC signal) and still provide enough oomph to the chip???
If it could be made to work reliably, it would be elegantly simple, intriniscally safe and the pickup assembly could be made split for slipping onto the conductor with a finishing turn of metal foil sticky tape to complete the earth shield.
It's a massive conjecture because I've always been crap at analogue stuff...
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A Y rated capacitor voltage divider driving a fet would be far simpler and meet more legal requirements.
NT
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NT wrote:

That's effecitvely what I proposed, only the capacitor is formed between the wire's insulation and the plastic between the sensing electrode and and the earth shielding.
I was trying to meet the objective of total isolation, hence no direct contact with the conductor.
Interesting idea with the FET - that could help. Still need to convert the AC signal to a damped DC one though otherwise the chip is going to have a hard time deciding if the power is "on".
Cheers
Tim
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Your proposal lacked a Y rated dielectric or any approvals. Converting 50Hz to dc is fairly trivial, if necessary.
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NT wrote:

Are you saying that the conductor's insulation is untrustworthy?
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I'm saying its required by law to be a class Y dielectric
NT
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NT wrote:

Coming back to common sense, I'd feel happier with applying a detector sleeve over inulation that iteself meets the voltage requirement, rather than directly connecting a class Y capacitor. It's not the capacitor that's the risk, but engineering out other problems like, say, condensation getting on the PCB where the capacitor is mounted.
If you were manufacturing these, you'd test the prototype and probably apply coatings or potting to avoid this problem.
For a DIY solution, I'd much rather have a non contact solution as proposed, or use a relay in a box with space.screw terminals where I can visually confirm the isolation.
Saying the cap must be class Y is one thing, but it's meaningless unless you can verify the installation of it.
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Do you know what a Class Y cap is?
NT
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NT wrote:

Yes. What's that got to do with my argument?
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Tim Watts

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Anything capacitive will be horribly subject to transmitting any noise, usually many orders of magnitude more effectively than the signal you're actually interested in.
Use an opto-isolator, which mostly give you 4kV isolation and no differential grounding problems. If you select a part with darlington output, you can switch it with as little as 1ma driving the LED side, which you can easily derive from the mains with a dropper resistor, and some rectification or a protection diode, and a fuse for safety. If the DS2413 has an internal pull-up or pull-down, you could connect the opto isolator directly. Otherwise, you'll need to handle providing a pull-up or pull-down and micopower from the 1-wire bus.
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Andrew Gabriel
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4N25 is ancient and has poor gain by today's standards. I would look at something like TLP523 instead.
JEDEC covers case styles, and in some cases pinouts for common parts.

Looks interesting, but I've never used it.
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Andrew Gabriel
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On Sun, 8 Jan 2012 00:16:51 +0000 (UTC), Andrew Gabriel wrote:

The MID400 looks the way to go for this project I think. I've also noticed the 8 channel 1-Wire IO chip as well, there are at least 4 mains powered devices I want to monitor.
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Dave.




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On Sat, 07 Jan 2012 22:29:40 +0000, Dave Liquorice wrote:

Doesn't that just provide a convenient way of detecting that AC is available, rather than "being used by something"? (it's the latter I'm interested in, and I thought the OP too...)
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On Thu, 12 Jan 2012 13:45:32 +0000 (UTC), Jules Richardson wrote:

I am the OP and am happy to make the assumption that if there is mains on the wire directly connected to a pump that the pump is running...
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Dave.




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On Thu, 12 Jan 2012 16:52:45 +0000, Dave Liquorice wrote:

Yes, I got hung up on the "monitoring" side of it and missed the "detect the presence of mains" bit in the first paragraph :)
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