How to Send an Analog Value to an Actuator in PLC Programming

How to Send an Analog Value to an Actuator in PLC Programming

One of the most important concepts in industrial automation is controlling actuators using analog outputs. Unlike digital outputs that are simply ON or OFF, analog outputs allow precise control of speed, position, flow, pressure, and temperature.

This infographic explains the complete process of converting an engineering value into an analog signal that an actuator can understand.

Step 1 – Determine the Required Signal

Most industrial actuators use:

4–20 mA

0–10 V

These signals are commonly used by:

Frequency Converters (VFDs)

Control Valves

Burner Controllers

Variable Speed Fans

Heating Systems

Step 2 – Create the Engineering Value

The PLC first calculates the required output value.

Examples:

• Motor Speed = 75%

• Valve Position = 40%

• Burner Capacity = 65%

These values are usually stored as REAL variables.

Step 3 – Scale the Value

The PLC converts the engineering value into a raw output value that the analog output module can process.

Example:

75% Speed

↓

20736 Raw Value

↓

16 mA Output Signal

Proper scaling is essential for accurate control.

Step 4 – Write to the Analog Output

The raw value is written to the analog output address.

Examples:

QW64

QW66

QW68

QW70

The analog module then generates the corresponding 4–20 mA or 0–10 V signal.

Step 5 – Control the Actuator

The actuator receives the analog signal and responds proportionally.

Examples:

VFD runs the motor at 75% speed

Valve opens to 40%

Burner operates at 65% capacity

Real Industrial Examples

The infographic demonstrates practical applications including:

• Frequency Converter Speed Control

• Control Valve Positioning

• Burner Modulation

• Process Control Systems

• PID Applications

Signal Flow

HMI Spoint

↓

PLC Logic

↓

Scaling

↓

Analog Output

↓

4–20 mA / 0–10 V

↓

Actuator

Key Principle

The PLC does not directly send percentages.

It converts engineering values into raw output values that are transformed into electrical signals by the analog output module.

Proper scaling and correct wiring are critical for reliable and accurate control.

Understanding analog outputs is essential for every PLC programmer working with process control, VFDs, valves, burner systems, pressure control, flow control, and advanced automation projects.