Isolated IO modules

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We're building a system that in its prototype form needs to isolate
a couple of 0-10V analogue signals from the outside world, at a
bandwidth of about 20-100kHz, low-voltage isolation only <1000V,
only for fault protection for a very expensive DSP.

The real system will have some stuff integrated on a board somewhere
but for the prototype testing I'd like to cobble something together from
some sort of pre-build modules, at reasonable cost.  I guess I can
get DIN-rail mounted modules that need a power supply and have 0-10V
inputs and outputs, but never having used them before I don't really
know where to start looking except in a random fashion through Google,
and that doesn't really give much of an indication of quality!

Digital IO would be nice, too, but I could get by with a bit of veroboard
and a few optos.  I don't really want to go that far with the analogue
stuff, though, if I can avoid it.

Does anyone who has used that sort of thing before have any suggestions,
please, preferrably for stuff available in the UK?


Trevor Barton
Isotek Electronics Ltd, 9 Clayton Wood Bank, Leeds, LS16 6QZ, UK.
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Re: Isolated IO modules

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Take a look at the HCPL7800 optically isolated analogue amplifier. They
are quite innexpensive and will isolate to 2.5kV IIRC (will have to check
the datasheet to be sure). Even so, I would consider adding further
protection networks around this on both sides of the barrier.

(stitche the above two lines back together as a sibngle line for a direct

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Re: Isolated IO modules
I usually isolate at the digital side.
If you use a serial ADC and digital isolation, this is easy.
The last time I did it I used LTC1860 12 bit serial ADC and HCPL-09XX family

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Re: Isolated IO modules
Isolating after digitizing is what's generally done, as inexpensive
optoisolators are much happier being digital than being analog.  This is
particularly cost-effective if your A/D converter is serial out.

Analog isolation is usually a bit expensive, but may be cheaper than
using a bunch of digital optoisolators if your A/D converter is parallel
out.  I just took a look at Digikey here in the US, and the isolation
amplifiers with 1kv isolation look to be as inexpensive as US$12.00 or
so.  The other issue with isolation amplifiers is that they tend to have
behaviors that may cause trouble if you're not experienced and careful.

As to *precisely* how to do this, in your instance, it depends on the
rest of your circuit.  Also, and unfortunately, I'm not familiar with
the parts availability in the UK.

Sorry to be vague, but it's a pretty large topic to answer in a short

Good luck!

Al Cohen

Trevor Barton wrote:

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