Recently, Somebody Somewhere wrote these words
> Hi everybody,
>
>
>
> It is suggested to our company to make a design of some test equipment
> for
> testing functionality of data acquisition systems for industrial
> automation
>
> (from different suppliers).
>
>
>
> The systems that must be tested can have, in particular:
> 1) 4..20mA inputs;
> 2) Inputs for RTD sensors, 3-wire and 4-wire.
> So we must have in our test equipment 4..20mA outputs, and some
> circuits, that will simulate RTD. I hope, that we can solve both of
> these problems.
> But we are not sure that in the case when our outputs are not
> galvanically isolated from each other, we do not run into problems
> with some systems.
> From the other side, galvanically isolated outputs will be more
> expensive and will have less precision. It is much better to have
> isolated groups of channels.
> Can somebody help to solve this dilemma?
>
> May be, it is impossible or very rear case, when the equipment for
> industrial automation will not work with single ended 4-20mA outputs
> or RTD's that are connected with each other? I suspect, that it is
> true, but am not sure.
>
You are in effect asking us what your design specifications are. You
have them. Read!
The problem here is that you will design what _you_ think the customer
wants, which is rarely what _the_customer_ thinks he wants, which is
only very rarely what the customer _actually needs_.
This is the joy of being a designer. Have fun. I think you need
galvanic isolation. To hell with the expense.
--
With best Regards,
Declan Moriarty.
--
Author: Declan Moriarty
INET: [EMAIL PROTECTED]
Fat City Hosting, San Diego, California -- http://www.fatcity.com
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