An Elspec is an FTP server, so to link to PNPSCADA, it needs a static IP.
Alternatively, you can use DNS:
to load an Elspec on your system, the correct way is to have a Public Internet IP Address (that gets patched through to a private subnet IP address in the customer's network).
This is however very expensive, so as an alternative, you can use a service called DynDNS (a free one is here: http://www.dyndns.co.za/).
You need to register an account there.
The account name is then entered into the Elspec when it is set up.
Keep in mind that a free DynDNS may fall away at any time, and then you need to use another one and reprogram the Elspec.
Once this is done, you can enter the name provided by the DynDNS as the IP address when loading the Elspec.