PLC Steps – Your Guide to Industrial Automation

This chapter presents two real-world examples using Functions (FC) in TIA Portal to demonstrate basic logic handling and analog value scaling using SCL.

• In the first example, we use a BOOL input to set two status outputs.
• In the second example, we process an analog signal using NormX and ScaleX instructions, with additional logic for alarm thresholds.

Example 1 – Digital Input to Online/Ofline Status

Objective

Create an FC that:

• Accepts a BOOL input (e.g. a connection status).
• Outputs two BOOL signals: Online and Ofline.
• Logic
  • If the input is TRUE, Online := TRUE and Ofline := FALSE.
  • If the input is FALSE, Online := FALSE and Ofline := TRUE.

Block: FC_DeviceStatus

Interface

Name	Type	Data Type
Connected	IN	BOOL
Online	OUT	BOOL
Offline	OUT	BOOL

Logic (SCL or Ladder):

Example Implementation – Choose One Method SCL or Ladder, not Both

Call FC to OB1 (drag and Drop) – Set PLC tags from Input and Output

Input = False, Online= False, Ofline = True

Input = True, Online= True, Ofline = False

Example 2 – Analog Scaling with Alarm Levels

Objective

Create an FC that:

• Takes an INT input representing a raw analog value (e.g., from 4–20 mA input).
• Uses NormX and ScaleX to convert the raw signal into a scaled value (0–100).
• Sets:
  • Alarm := TRUE if the scaled value is less than 20
  • Warn := TRUE if the scaled value is between 21 and 30

Block: FC_AnalogMonitor

Interface

Name	Type	Data Type
RawInput	IN	INT
ScaledValue	OUT	REAL
Alarm	OUT	BOOL
Warn	OUT	BOOL
normVal	Temp	REAL

Logic (SCL):

Example Implementation

Summary

FC	Purpose	Key Concepts USed
FC_DeviceStatus I	Basic digital logic	F, BOOL output control
FC_AnalogMonitor	Analog scaling + alarm thresholds	NormX, ScaleX, IF, REAL math

These examples demonstrate the power and flexibility of using Functions (FC) with SCL to encapsulate

These examples demonstrate the power and flexibility of using Functions (FC) with SCL to encapsulate.

Status Healthy

Warn Present

Alarm Present

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