The SPACOM devices, e.g. the relays and the annunciator units are connected to the fibre-optical SPA bus by means of bus connection modules. The bus connection module SPA-ZC22 converts the optical signals of the SPA bus to RS 485, SPA (+5 V) or RS 232 signals and vice versa. The bus connection module is provided with a built-in power unit allowing the SPACOM device to be disconnected from the bus connection module, for instance, for service without interrupting the data communication over the optical loop.
The bus connection module is provided with one 9-pin D type subminiature connector for RS 485 or SPA connections, one 25-pin D type to order, two or five opto-connector couples for fibre-optical cables. The fibre-optical links can be based on glass fibre cables, plastic core cables or both types mixed.
The bus connection module is mounted in a suitable place in the apparatus cabinet and the connection cable of the module is plugged to the D-type connector on the rear panel of the SPACOM device. The bus connection module type SPA-ZC22 connects to any SPACOM device provided with a D-type connector. The bus connection module can also be connected to the master units, such as substation level units SACO 148D4 and SRIO 1000M, of the communication system.