Detailed Explanation of Digital, Analog, and Pulse Signals
Digital signals, analog signals, and pulse signals are three very common types of signals used in automation systems.1. Digital Signals (Discrete / Switching Signals)Digital signals (also called switching signals) have only two possible states:[*]0 or 1
[*]ON or OFF
[*]Presence or absence
In other words, there are only two results.Typical input examples
[*]Push buttons — pressed / not pressed
[*]Proximity sensors — object detected / not detected
[*]Limit switches — triggered / not triggered
[*]Counting detection — pulse received / not received
Whenever a signal has only two states, we use digital input.Typical output uses
[*]Motor start / stop
[*]Lamp ON / OFF
[*]Solenoid valve open / close
2. Analog Signals (Continuous Signals)Analog signals are values that continuously exist and continuously change.Examples:
[*]Temperature
[*]Pressure
[*]Weight
[*]Liquid level
[*]Speed (variable control)
You cannot say “temperature exists or not”; it is always present and changing.
Therefore it is called an analog quantity.How analog values enter a control systemPhysical quantities must be converted into electrical signals:Common standards:
[*]Current: 0–20 mA, 4–20 mA
[*]Voltage: 0–5 V, 0–10 V
ExampleA temperature sensor range: 0–100°C → 0–10 V
TemperatureVoltage
0°C0 V
30°C3 V
100°C10 V
So when the controller receives 3 V, it calculates the temperature as 30°C.Pressure, weight, and level work the same way.Analog output controlUsed when the target has adjustable levels:
[*]Valve opening: 0–100%
[*]Motor speed control
[*]Force control
[*]Heating power control
Example:
0–10 V controls valve opening
5 V → 50% open3. Pulse Signals (High-Speed Digital Signals)Pulse signals are actually a special type of digital signal —
but continuous and regular.Like a heartbeat: continuously ON and OFF in a regular pattern.Typical uses
[*]Encoders
[*]High-speed counting
[*]Position measurement
[*]Stepper/servo positioning
If 10 pulses = 10 units of movement
Receiving 10 pulses means the object moved 10 units.Speed control using pulsesSpeed depends on pulse frequency:
[*]Send 10 pulses in 1 second → fast movement
[*]Send 10 pulses in 1 minute → slow movement
So controlling pulse interval = controlling speedSummary
Signal TypeCharacteristicsTypical Use
DigitalOnly ON/OFFSwitches, sensors, start/stop
AnalogContinuous changing valueTemperature, pressure, speed
PulseRegular repeated digital signalCounting, position, encoder
Understanding these three signal types is fundamental in automation because every PLC system processes inputs and outputs using one (or a combination) of them.
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