Passing analog signals to floating platform?

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Liam David
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Passing analog signals to floating platform?

Post by Liam David »

I need to pass analog signal(s) to electronics floating at high voltage (100kV). Anyone know of cheap (<~$100) simple ways to do this? Optical USB cables exist but they tend to be expensive. The floating electronics are battery-powered.
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Richard Hull
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Re: Passing analog signals to floating platform?

Post by Richard Hull »

Are these DC analog signals? If so, you would have to employ a VFC (voltage to frequency converter) then, in theory, you could capacitively couple this to a FVC (frequency to voltage converter). Not a tough task as many IC's exist to do this. The beauty is that the analog DC level is set by the frequency, thus a 1 volt P-P signal sent through a capacitor or fiber optics arriving as a .25 volt P-P signal would still give an accurate DC level at the down convert receiver. DC levels at the VFC can be set at the output of the FVC. Did this a few times at work when there were no IC's to do the job with ease. Had to hand wire with discrete components at each end back in the 70's. Still, for the time it was not a tough project, just a time consuming one as all were one-off projects and not an OEM effort for market.

If the analog signal is FM frequency modulated just a capacitor would do.

Fiber optics is the way to go in a monstrously noisy environment.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Liam David
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Re: Passing analog signals to floating platform?

Post by Liam David »

Thanks for the suggestion Richard, I like the idea. You're correct in that I meant DC analog signals. I'll definitely be using fiber.
Justin Fozzard
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Re: Passing analog signals to floating platform?

Post by Justin Fozzard »

A few years ago I needed to monitor the voltage and current supplied to the cathode heater of a magnetron while it was being pulsed at 60kV (100A, 10us/1000pps).

I used some LM331 voltage to frequency converters to drive Agilent Versatile Link fibre optic connections and found the method to be surprisingly linear and accurate over the whole 20V/20A filament supply range.
The prototype transmitter was housed in a small diecast box and ran off AA batteries so that it could be floated at 60kV.
Here are schematics for the device:
Heater Monitor Circuit - Transmitter.pdf
(438.26 KiB) Downloaded 26 times
Heater Monitor Circuit - Receiver.pdf
(428.57 KiB) Downloaded 28 times
Heater Monitor Circuit - Transmitter.jpg
Heater Monitor Circuit - Receiver.jpg
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Richard Hull
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Re: Passing analog signals to floating platform?

Post by Richard Hull »

Sounds like Justin has just supplied a modern solution using more modern components, all pretty cheap and easy to get.
Simply adapting, as needed, his circuit is the way to go.
This is a real share where a need is solved. Thanks Justin.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
richnormand
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Re: Passing analog signals to floating platform?

Post by richnormand »

There also exist solutions (industrial mostly) where you can use the average light intensity (or even a different light wavelength from the signal carrier) via the fiber to supply the needed DC voltage at the other end from the photodetector. This would eliminate the need for batteries at the HV end.
depends on how complicated you want/need to go.
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Liam David
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Re: Passing analog signals to floating platform?

Post by Liam David »

Thank you all for the suggestions! I have some work ahead of me.
richnormand
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Re: Passing analog signals to floating platform?

Post by richnormand »

just another thought:
You could also use two fibers. One for signal and one with a more powerful laser and photodetector to generate the DC needed at the other end and eliminate the batteries.
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Re: Passing analog signals to floating platform?

Post by Oscar Anderson »

The easiest way to do this is using verstile link (or even cheap toslink) fiber optic transceivers. There are a number of ways to do PWM generation, probably the easiest for beginners is with an Arduino, but it can be done with any number of SMPS controller ICs or even discrete transistors if you feel so inclined.

On the receiver side, you just need a low-pass filter - no frequency-to-voltage converter. The dynamic range and bandwidth aren't anything too spectacular, but it's good enough for power supply control and basic instrumentation, and it's simple, robust and cheap.


For floating isolated power, the method that's been used for many of the NBI systems I've encountered is to use a 20 kHz power oscillator, roughly 15 - 20 V in amplitude, driving a transformer wound using HV cable. The core is ferrite (typically), and running at 20 kHz allows you to get the number of required turns down. Use fast recovery rectifiers on the secondary side. The 20 kHz power oscillator can be implemented pretty easily using a 74HC14 oscillator and a couple of gate drivers.
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Liam David
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Re: Passing analog signals to floating platform?

Post by Liam David »

Thanks Oscar, all good ideas and it's always nice to know how the 'pros' do it. I'm working on testing a simple toslink-based system.
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Re: Passing analog signals to floating platform?

Post by John Futter »

I've done the analog v to f and f to v over fibre optic but there are bluetooth / wifi and other options now
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