Parameter Initialization when Power UP

PLC Program for Automatic Parameter Initialisation on Power-Up

This document outlines a PLC programming solution for automatically initializing critical parameters upon machine power-up, preventing data loss due to power failures and enhancing operational efficiency.

Problem Description

In industrial applications, certain machine parameters (e.g., set speed, batch size, target position) often require specific initial values for proper operation. A common challenge arises when power interruptions occur, potentially causing these parameters to reset to zero or retain incorrect values. This necessitates manual re-entry of data by the operator every time the machine powers up or recovers from a power failure, leading to downtime, potential errors, and reduced productivity.

The objective is to ensure that essential machine parameters are automatically initialized to predefined values whenever the machine is powered on, eliminating the need for manual intervention in such scenarios.

Diagram:- 

Problem Solution Approach

To address this, we will implement PLC logic that automatically initializes parameters during the PLC's first scan after power-up. Additionally, a manual initialization button will be provided, allowing operators to reinitialize parameters during normal machine operation if needed.

For demonstration purposes, we will consider "Machine Set Speed" as the parameter to be initialized. It will automatically set to a default value on power-up, and an operator can manually adjust or reinitialize it via a button during runtime.

Hardware and Software

• PLC: Siemens S7-1200

• Programming Software: Siemens TIA Portal

List of Inputs/Outputs

Type	Address	Description
Input	I0.0	Parameter Initialization Button
Memory	MW10	Set Speed (from HMI/Display)
Output	MW12	Speed for Drive (Actual Speed Command)

PLC Program Description

The program utilizes the S7-1200's system memory capabilities, specifically the "First Scan" bit, to trigger automatic initialization. The system memory bits (Always ON, Always OFF, First Scan, Diagnostic Status Changed) are internal bits provided by the PLC for specific system states. Here, we configure M1.0 as the First Scan bit.

Network 1: Automatic and Manual Parameter Initialization

This network handles the initialization of the MW12 (Speed for Drive) parameter.

• We use a Normally Open (NO) contact of the First Scan bit (M1.0). This contact is active only for one scan cycle immediately after the PLC transitions from STOP to RUN mode (e.g., on power-up or after a manual restart).

• When M1.0 is active, a MOVE instruction is executed. This instruction moves the initial default value (e.g., 5 RPM) into MW12 (Speed for Drive). This ensures that the motor starts at a safe, predefined speed automatically upon power-up.

• Additionally, a Normally Open (NO) contact of the Parameter Initialization Button (I0.0) is connected in parallel. If the operator presses this button during runtime, it will also trigger the MOVE instruction, reinitializing MW12 to 5 RPM, providing a manual override.

Network 2: Manual Data Entry for Runtime Adjustment

This network allows the operator to modify the machine's set speed during normal operation.

• This logic enables the operator to enter a desired speed value into MW10 (Set Speed from Display) via an HMI (Human Machine Interface) or display unit.

• A MOVE instruction then transfers the value from MW10 (Set Speed from Display) to MW12 (Speed for Drive).

• For example, if the operator enters 100 RPM into MW10, this value will be moved to MW12, causing the motor to run at 100 RPM. This allows for dynamic adjustment of the speed during the running cycle, independent of the automatic initialization.

Runtime Test Cases

Input Condition	Expected Output (MW12)	Physical Element Behaviour
PLC Power-Up (First Scan M1.0 becomes 1)	5	Motor runs at 5 RPM (initial)
Operator enters 100 into MW10	100	Motor runs at 100 RPM
Parameter Initialization Button (I0.0) pressed	5	Motor reinitializes to 5 RPM