Analog vs Digital Inputs — Basic but Very Important
Every PLC/DCS engineer must clearly understand this difference 
Digital Input (DI)
Reads only 2 states
ON / OFF
1 / 0
TRUE / FALSE
Examples of Digital Inputs
Push buttons
Limit switches
Proximity sensors
Motor run status
Signal is either ON or OFF
Analog Input (AI)
Reads continuous varying values
Not just ON/OFF
Actual measurement values
Examples of Analog Inputs
Temperature transmitter
Pressure transmitter
Flow transmitter
Level transmitter
Typical signals:
4–20 mA
0–10 V
Key Difference
Digital Input → Discrete state
Analog Input → Continuous value
Real Example
Tank Low Level Switch → Digital Input
Tank Level Transmitter → Analog Input
Important for PLC engineers
Digital signals are simple
Analog signals require:
Scaling
Filtering
Calibration
Simple understanding
Digital = YES / NO
Analog = HOW MUCH?
Every automation system is built using a combination of Analog + Digital signals
Video
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