Explain equal instruction using example

Explain equal instruction using example

Application:-Explain Equal instruction in the PLC. Write PLC program for explanation using ladder diagram language.

Components:-Programmable logic controller, HMI panel, wires, 24 VDC lamp, 24 VDC power source.

Diagram:-

Explanation:-

Consider a simple example for explanation of equal instruction in the PLC. Here we have taken simple HMI (Human Machine Interface) for display and programmable Logic Controller (PLC) for programming. Take two value set value 1 and set value 2 for example. Here if both the value in the set value 1 and set value 2 equal then lamp will be ON. So we need to use == instruction for above example.

Enter 50 value in the set value 1 box and enter 50 value in the set value 2 box so lamp should be ON and if someone enter 25 value in the set value 2 box, lamp should not be ON.

PLC program:-

Write the ladder program for above application using ladder diagram language. Here for ladder logic we can use any supported PLC system like S7-1200, S7-300, S7-1500 or any other PLC which can support this instruction. For PLC logic we need digital inputs and outputs.

For our application lamp is digital output. Two set values from the HMI are input words.

Digital Output:-

Lamp=Q0.0

M Memory:-

Set value 1:-MW10

Set Value 2:-MW12

PLC program Explanation:-

In network 1 we tow values are compared with comparison instruction. Set value 1 (MW) is compared with Value 2 (MW12).Hence if both values are equal, lamp (Q0.0) will be ON.

In comparator instruction, two operands are compared, we can set data time in comparator instruction.

Latching and unlatching Circuit.

PLC Program for Latching and Unlatching Circuit

Problem Description:

In many basic conveying or water-filling systems, the operator manually controls a water pump to fill a tank. This requires the operator to:

• Start the pump manually and wait while the tank fills.
• Monitor the tank level continuously.
• Stop the pump manually when the tank reaches the High-Level sensor.

This approach is inefficient and prone to human error.

 

Automation Requirement:

The system should:

• Allow the operator to start the pump manually with a push button.
• Keep the pump latched ON (i.e., running continuously) after the button is released.
• Automatically stop the pump when the tank reaches the High-Level (sensor).
• Prevent the pump from restarting until the operator initiates it again.

 

Example Scenario:

Let’s consider a manual water conveying system where:

• A START pushbutton is used to begin pumping.
• A High-Level float sensor detects when the tank is full.
• A STOP condition is automatically triggered when the tank reaches this level.

Problem Diagram

Problem Solution

In this application, we consider a storage tank that is filled using a water pump. The system is equipped with the following components:

• One high-level sensor to detect when the tank is full.
• A control panel with:
• A START push button (PB) to manually start the pump.
• A STOP push button (PB) to stop the pump manually if needed.

The operation is as follows:

• When the operator presses the START PB, the water pump is energized to begin filling the tank.
• The pump continues to run until the high-level sensor detects that the tank is full.
• Upon detecting the high level, the sensor sends a signal to automatically stop the pump.
• This sequence is implemented using SET and RESET (Latch/Unlatch) instructions in the PLC to maintain the pump state between operator actions and sensor inputs.

Although the actual system includes a manual discharge valve for emptying the tank, it is not included in the logic control for this program.

Note: This same logic can also be implemented using relays in conventional control panels.

 

Program

Here is PLC program for Latching and unlatched circuit for output.

 

Network 1

 

Network 2

List of Inputs and Outputs

Input

Signal Description	Address
START Push Button	I0.0
STOP Push Button	I0.1
High-Level Sensor	I0.2
Low-Level Sensor	I0.3

 

Output

Signal Description	Address
Water Pump	Q0.0

 

Program Description

For this application, we are using a Siemens S7-1200 PLC programmed with TIA Portal software. The same logic can also be implemented using conventional relay-based circuits.

This program demonstrates a latching and unlatching circuit, commonly used in fluid control applications.

Network 1: Latching Logic (SET Instruction)

The START push button (I0.0) is used to start the water pump (Q0.0).

When pressed, it activates the SET instruction, latching the pump output (Q0.0).

A normally open contact of the Low-Level sensor (I0.3) is placed in series with the START PB to ensure the pump only starts if the tank is not already full.

A normally open contact of the Water Pump output (Q0.0) is also included to maintain the latched condition once the START PB is released.

 

Network 2: Unlatching Logic (RESET Instruction)

The High-Level sensor (I0.2) is used to stop the pump automatically when the tank is full.

A normally open contact of I0.2 is used with the RESET instruction to unlatch the output (Q0.0).

For manual stopping, the STOP push button (I0.1) is connected in parallel with the High-Level sensor input, providing an alternative way to reset the pump.

Runtime Test Cases

Inputs Condition	Output	Physical Result
I0.0 = 1 & I0.3 = 1	Q0.0 = 1	Water Pump ON
I0.1 = 1	Q0.0 = 0	Water Pump OFF (Manually)
I0.2 = 1	Q0.0 = 0	Water Pump OFF (Auto-Stop)

 

Explain greater than instruction using example

Application:-Explain greater than instruction in the PLC. Write PLC program for explanation using ladder diagram language in the Programmable Logic Controller (PLC).

Components:-Programmable logic controller, HMI panel, wires, 24 VDC lamp, 24 VDC power source, 24VDC temperature controller.

Diagram:-

Explanation:-

Consider a simple temperature controller example for explanation of greater than (>) instruction in the Programmable Logic Controller (PLC). Here we have considered simple HMI (Human Machine Interface) for display and programmable Logic Controller (PLC) for programming. Consider one temperature control which is displaying the temperature given by temperature sensor, here we haven’t considered analog signal calculation and scaling so we directly consider actual value in the PLC. Here if the actual temp value in the actual temp box is greater than set temp, temperature indication will be ON.

If set temperature is 100 degree and temperature read by temperature controller is more than 100 degree or consider 102 degree, lamp should be ON because 102 degree is greater than 100 degree.

PLC program:-

Write the ladder program for above application using ladder diagram language. Here for ladder logic we can use any supported PLC system like S7-1200, S7-300, S7-1500 or any other PLC which can support this instruction. For PLC logic we need digital inputs and outputs.

For our application lamp is digital output. Set temp is the input word.

Digital Output:-

Temp Lamp=Q0.0

M Memory:-

Set temp.:-MW10

Actual temp:-MW20

PLC program Explanation:-

In network 1 actual temperature (MW10) will be compared with set temperature (MW20). So if the measured temperature (MW10) is greater than set temperature (MW20), temperature indication lamp (Q0.0) will be ON

In greater or equal (>) instruction, two operands are compared, we can set data type in comparator instruction.

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