Current and Voltage Display in DCS

"Are this signals are analog signals?"

The signals would be considered analog signals as opposed to discrete (on/off). The type of telemetry employed will depend on the capabilities of your metering/monitoring devices. GE Multilin and ABB (all manufacturers these days) relays and metering devices have 2 possibilities;

1. The use conventional 4-20mA outputs from these devices in which case each signal will require its own pair of wires on which to transmit the signal to the DCS (as an analog input).

2. The sue of serial (modbus) communication in which case the appropriate cable is required and the slave devices can be multi-dropped (daisy changed) with one cable connected to a serial interface on the DCS, ofcourse there will be a limit to the number of devices than can be connected via one line (i.e. to one serial input) but this will be defined by the DCS manufacturer. This usually takes some effort since addressing and configuration is critical but there are significant advantages.

Serial communication is widely accepted and ideal for this type of application since these are mainly indication loops on your system and so are deemed non-critical to plant operation and up-time.