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Summing amp to inject a signal onto AC?

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large_ghostman

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I cant remember much about this, so wild guess time.............

If I want to inject some digital signal onto a AC waveform, I can use a summing amp? Or inverting amp depending on the situation, is this correct or am I away on one?
 

JimB

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What digital signal, what AC waveform, why.

JimB
 

large_ghostman

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Sign wave 300Hz and just serial data short bursts.

Why............

One signal on a wind turbine panel is 24V 300Hz, it goes to the main control panel some distance away, no idea why wireless or cable isnt an option but it isnt. So I wondered if the data could be injected on top the sign wave. I dont know a huge amount about the turbine, its small and pretty old. I have absolutely zero idea why its 300Hz, but there you go. All it really needs to do is send information once an hour.

Hopefully I will get more info at some point, I was just looking for a way to do it without using another cable. I asked about wireless (my first option) but apparently no chance.
 

large_ghostman

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Oh and the serial data would be best if it could be sent at a different rate, kind of like 2-3 channels if you see what I mean. One for each sensor.
 

crutschow

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You can couple the sensor digital signal into the AC signal through a capacitor that's large enough to have a low impedance to the digital waveform but small enough to not significantly couple the 300 Hz back into the digital source driver.

At the receiving end you can use a similar capacitor to detect the signal.
You may have to put an inductor in series with the line at the receiving end that has a high impedance to the digital signal and a low impedance to the 300Hz to be able to recover a reasonable signal level.

As far as sending different signals, you can just send an initial word that identifies which sensor signal data is to follow.
All the housekeeping, and signal generation and recovery, could probably be done best with a micro at each end, using one of the standard serial digital protocols built in to the micro.
 

ChrisP58

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Is the 300Hz a low power signal, or is it the output power from the turbine?

If it's a low power signal, then your summing amplifier idea might work. But if it's the output power from the turbine, you'd need a power amplifier after the summing amp.
 

large_ghostman

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Its a low power signal, the original idea was some kind of information...detection system. The project was never completed properly so the actual control panel is half completed. The turbine is working and has been for ~8 years. Not 100% sure what they intend to do with it, but rules have changed and they want a read out from the sensors to the panel.

I have zero idea why the signal is, what it is or why it was done that way. But its the only cable or point within the panel, I could reasonably connect to. Thanks for the help, the micro idea might be a good option. The turbine is one from the site I used to look after, it was the old very small one they kept. My input at the moment was just to suggest a way of doing what they want, Although I am probably just unlucky enough to get picked to do it lol.

They also want 300 meter of the armoured cables removed from the turbine we took down. That will get stuck in the barn for rainy day :D.
 

MikeMl

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Is the 300Hz AC the main output for the turbine? i.e. is what carries the power from the turbine to some load? If so, it will require some special techniques to piggy-back a "rf carrier" onto what is very low impedance low-frequency circuit, otherwise the low-impedance will "short-out" the information you are trying to superimpose. I would need to know a lot more about the existing system before suggesting something...
 

schmitt trigger

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Data over powerline has been around for many years now. The reasoning is simple economics: if you already have a pair of wires in place, you can use them for communication, no need for the extra expense and difficulty of additional wires.

In the late 70s and early 80s there was a home automation protocol called X10 utilizing existing home power wires as data carriers. It was actually invented by a Scottish company, see here: http://buildyoursmarthome.co/home-automation/protocols/x10/

So perhaps what you are seeing is a variant of the protocol.

But as numerous web articles describe, the X10 protocol wasn't very reliable, and has been largely superseded by wireless protocols.
 

large_ghostman

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No Mike the 300Hz isnt mains, its 24V. I havnt been able to get to the actual turbine yet (really swampy between the site and panel). No one has any idea what the cable is for, the turbine panel never got finished so the cable just hangs inside it. The Turbine goes to a inverter near the turbine, apparently that is single phase (240V 50Hz). there is also 24V DC that goes back to the panel, but that is a power cable for some kind of 24V battery system.

This thing is over 12 years old, its also a mix of systems, or what they call a 'country job' around here :D. I have an awful feeling they will add to the turbines at some point, nothing including the turbine is connected to the national grid. But I do think somewhere it is connected to a battery bank, maybe the 300Hz has something to do with that. But I honestly dont know.

Waiting for the ground to dry a little (month or two), then I can get across to where the turbine and shed is.
 
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