EM0VE (John) wrote in message ...
serial cable adapter

Maybe it was a crossover cable? Most devices on ethernet need a
hub/switch/router between them. Device X Computer or Device=Hub=Computer, X
standing for crossover cable.
~John

I am sorry that my level of technical understanding is low.
Here is the description of the product from the Neptune Systems
webpage:

Ground Isolated Serial Connector
The ground isolated serial connector (SERIPC9) is used to break ground
loops between your PC and the AquaController. In some installations a
ground loop is formed when a serial connection is made and can cause
erroneous pH and ORP readings. This ground loop can be broken by
installing a GISC in the series with the serial cable from the
AquaController. If the serial cable is going to be permantly hooked up
to the AquaController, then the GISC is recommended. The GISC measures
1.5" x 1.25" x .65" and has one male DB9 connector and one female DB9
connector. Note that the GISC is only for use with the AquaController
or the AquaController 2.