INSTRUMENTATION SIGNALS
The instrumentation signals are two types
•Analog signal •Digital signal
Analog Signal
Analog Input : DCS gets the input from field devices like transmitters.
Example: •transmitters like LT, PT, FT, TT etc
•VFD speed
•Vibration probe
•Gas detector
Analog Output : DCS sends command to control valve. Control valve positioner works at 0-100% and 4-20mA.
Example: •Control valve positioner
•Speed that we give to VFD
Digital Signal
Digital Input: It sends on/off signal in form of 0 and 1 to DCS.
Example: •Any type of switch like limit, pressure switch etc..
•Compressor run feedback it comes from MCC
•Hooters
Digital Output: DCS give 0 and 1 command to solenoid operated valve, which on or off it.
Example: •SOV-on or off
•Pump-start or stop
•MCC(motar control circuit)