Isolated IO modules

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 link).

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 isolator.

Ltd.

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 posting.

Good luck!

Al Cohen

Trevor Bart> We're building a system that in its prototype form needs to isolate