Modular I/O (input/ output) devices allow a large number of voltage, mA, temperature and digital signals to be monitored or controlled by a remote computer or PLC. This type of system uses a base or network adapter to provide the power and communication with up to 32 modules, but requires only one Ethernet or RS485 port.
Measurements are communicated using Modbus or ASCII protocols over Ethernet or RS485 to the remote computer.