Analog Isolator

Check out these:

Make sure you sit down before looking at the price. Digikey has them in stock, singles cost over $80.

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Regards, Joerg

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Not to worry though, there are several application notes floating around the web for analogue isolators using ordinary opto-isolators.

Yes, but it depends on Howard's expertise, available time and whether it's for production. For a one-off unit I'd just buy it.

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Joerg wrote in news:PB%%j.2455$ snipped-for-privacy@flpi144.ffdc.sbc.com:

It does have the advantage of providing isolated power.

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Scott
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Yes, that's a neat feature. Although it's quite easy to do. Just take the output of a logic gate or if more oomph is needed take a gate driver chip and capacitively couple into one side of a LAN transformer, rectify and filter on the other side. In a pinch just wind some wire on a Fair-Rite #77 core.

I have done stuff like "borrowing" a LAN transformer out of a hub that didn't have all ports occupied (after getting client permission...). I bet it still has duct tape on that port :-)

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Or chop, send over a toroid and clamp to restore the DC-level on the other side. That what I always do. No feedback :-)

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You know that make them ready to go din rail mountable. They aint cheap however.!

If you're looking for something to make then use the Photo feed back optical couplers with

2 supplies and 2 separate op-amps. those track as close as the tolerance of the feed back diode.

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Well yeah, a PWM scheme works. We have some ready made units from KB that were originally designed to be used as a signal isolator to drive their cheap DC drives which don't have isolation from the bridge and mains. I find them all over the place in machines put there before my time at my current place of employment.

"

Thanks Joerg the AD215 looks very promising. I was looking for an analog isolator to replace a $349 isolator sold by National Instruments. Their isolator also required a $349 case. So $80 plus is a bargain. However, the isolator will be used by a novice and I am wondering if wiring to a SIP socket. adding gain resistors and a power supply might be to challenging. I would prefer an isolator that came in a package with screw terminals even it if costs twice what the AD215 costs. Once again this is a one of a kind item.

Howard

Try asking on sci.engr.control. This group is mostly aimed at folks like Joerg who stick chips on to boards, sci.engr.control would be a place for folks who buy boxes. I'm sure there are folks there who have purchased analog isolators, and may have some insight into the market.

--

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Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

In that case take a look at companies like this:

Much of this will be rack mounted though but in a heavy duty industrial environment that might actually suit better. Makes it easier to swap if something got hit by the forklift ;-)

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Please name a couple of suppliers of DIN rail mountable analog isolators. I want to give the user a choice between a more user required wiring type like the AD215 and a DIN rail mounted unit.

Thanks Howard

An example for DIN rail mounting would be these:

If slimline is preferred:

Also, check Johnson Controls.

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PWM works, but you need a reference voltage source on the sending side with which to compare the incoming voltage and and another voltage reference on the receiving side to turn the mark-to-space ratio back into an absolute voltage.

Joerg's transformer transmits an absolute voltage.

I once put together a scheme around a transformer with three windings

- you drove one winding and used local feedback to get exactly the desired voltage on second (local) winding, and monitored the voltage across the third (isolated) winding with a high-input impedance follower. Since there was very little current flowing through the second and third windings, the voltage was transferred very accurately (and cheaply).

You did need a sample and hold on the output to hold the output voltage while you wound down the flux through the core from time to time, so the bandwidth wasn't great.

-- Bill Sloman, Nijmegen

-- Bill Sloman, Nijmegen

Try Action in San Diego (now part of the same group as Eurotherm) or Wilkerson in central FL.

Best regards, Spehro Pefhany

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Not really. I never had voltage references on either side. Ok, except for the path that transferred isolated power. And even then only very occasionally.

On the other side you can clamp the DC level and, voila, there's the signal again.

I've transferred signals with spectral content up to 50MHz that way.

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The AD202 sounds like it might work and it's $40.00 cheaper.

What are they using to obtain such high common mode ranges,with so high an input impeadance? All the difference amp's I've seen with high common mode ranges have kohm input impeadances.

Well, the input part connected via isolated. Then you get tons of CM range.

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