Electrically isolated RS232 interface

The cable is by far the most widely used type of connection where electrical signals are to be exchanged between two pieces of equipment or larger systems. An inherent disadvantage of a cable is, however, that it brings the electrical potentials of the two systems in contact with each other, which can have many undesirable electrical as weil as electromagnetic effects. The latter, in particular, are not to be wavedaside, witness the recently enforced EMC (electromagnetic compatibility) regulations, aimed at reducing the levels of interference emanating from today's electrical equipment. With the aid of an electrically isolated interface it is still possible to exchange signals without a 'copper-to-copper' connection. Such an interface is described here: it is suitable for insertion into an RS232 link as used, for instance, in an automated, remote-Iogging data acquisition system, where it should help to reduce measurement errors caused by common-mode interference, which is always around.