Motor Operation Based on Time Cycle Sequence

A Practical Guide for Automation Professionals and Students

In industrial automation, motors are the backbone of countless processes—from conveyor systems and pumps to mixers and compressors. While many motor operations are triggered by sensors or manual inputs, time-based motor sequencing offers a powerful method for controlling multiple motors in a predictable, repeatable pattern. This approach is especially useful in applications where operations must follow a strict timeline, regardless of external conditions.

This article explores the concept of motor operation based on time cycle sequences, its implementation using PLCs, and its relevance in modern automation systems. Whether you're a student learning the basics or a professional designing control panels, this guide will help you understand and apply time-based motor control effectively.

What Is Time Cycle-Based Motor Operation?

Time cycle-based motor operation refers to the activation and deactivation of motors according to predefined time intervals. Instead of relying on external triggers like sensors or switches, the system uses timers to control when each motor turns ON or OFF.

This method is particularly useful in:

• Sequential operations (e.g., mixing, filling, packaging)

• Load distribution across motors

• Preventing simultaneous startup to avoid current surges

• Repetitive tasks with fixed durations

Example Scenario: Three-Motor Sequence

Let’s consider a simple example involving three motors (M1, M2, M3). The goal is to operate them in a specific sequence over a 30-second cycle:

Time Interval (sec)	Motor 1 (M1)	Motor 2 (M2)	Motor 3 (M3)
0–5	ON	OFF	ON
5–10	ON	OFF	OFF
10–25	OFF	ON	OFF
25–30	OFF	OFF	ON

This sequence repeats continuously as long as the system is active.

PLC Implementation: Ladder Logic Approach

To implement this logic, we use a Programmable Logic Controller (PLC)—such as Siemens S7-1200 or S7-300—with ladder logic programming. The system includes:

• START and STOP push buttons

• Timers (TON or TP)

• Motor output coils (Q0.0, Q0.1, Q0.2)

Visualization: Time Cycle Diagram

To help students and professionals visualize the sequence, a time cycle diagram is essential. It shows the ON/OFF status of each motor across the timeline, making it easier to understand and debug

Time (sec) → 0   5   10   25   30  
M1         → ────ON─────OFF────────  
M2         → ────────ON─────OFF────  
M3         → ON────OFF────────ON────

This diagram can be included in training kits, SCADA screens, or HMI interfaces to enhance clarity.

Real-World Applications

Time-based motor sequencing is widely used across industries. Here are a few examples

1. Conveyor Systems

In packaging plants, different conveyor belts may need to run in sequence to move products from one station to another. Time-based control ensures smooth transitions.

2. Pumping Stations

In water treatment facilities, pumps may operate in cycles to balance load and prevent wear. Time sequencing helps automate this process.

3. Mixing Operations

Chemical or food processing units often require ingredients to be added and mixed in a timed sequence. Motors controlling mixers and feeders follow a strict time cycle.

4. HVAC Systems

Fans and compressors in HVAC systems can be staged based on time to optimize energy usage and reduce peak loads.

Educational Value

For students and trainees, this topic offers a hands-on way to learn:

• Timer functions in PLCs

• Ladder logic programming

• Sequential control design

• Visualization and debugging techniques

It’s also a great opportunity to introduce real-time monitoring, HMI integration, and SCADA visualization, making the learning experience more industry-relevant.

Tips for Implementation

Here are some best practices when designing time cycle motor operations:

• Use retentive timers if the cycle needs to resume after power loss

• Label time ranges clearly in your code and diagrams

• Include manual override options for safety and maintenance

• Test with simulation tools before deploying on actual hardware

• Document the logic for future troubleshooting and training Integration with SCADA and HMI

To make the system more interactive and user-friendly, integrate the motor sequence with SCADA or HMI platforms. This allows operators to:

• View motor status in real time

• Adjust time intervals dynamically

• Start/stop the cycle from a touchscreen

• Receive alerts if motors fail to operate as expected

Platforms like WinCC, FactoryTalk, or InduSoft can be used to build intuitive interfaces.

Selective execution of the application

Automatic door system

Controlling of conveyors with interlock

PLC Program: Conveyor Sequence Control and Interlocking

Problem Description

A feeder drops material onto Conveyor 1, which then transfers the material to Conveyor 2 for further processing. The system must function automatically—conveyors should start based on material detection using load cells. The system must ensure sequence control and interlocking to avoid collisions.

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System Components and Setup

• PLC Type: Siemens S7-300

• Software: TIA Portal

• Material Detection: Load Cells (preferred over proximity or limit switches for higher reliability)

I/O List

Inputs

Address	Description
I0.0	START Push Button
I0.1	STOP Push Button
I0.2	Load Cell 1 (Conveyor 1)
I0.3	Load Cell 2 (Conveyor 2)

Outputs

Address	Description
Q0.0	Cycle ON Indicator
Q0.1	Conveyor 1 Motor
Q0.2	Conveyor 2 Motor
Q0.3	Feeder Motor

Ladder Logic Program Description

Network 1: System Start Logic

• When START (I0.0) is pressed and system is not in STOP mode (I0.1 not active), Cycle ON (Q0.0) is latched to keep the system running.

• This also starts the Feeder Motor (Q0.3) to begin dropping material.

Network 2: Conveyor 1 Activation

• If Cycle ON (Q0.0) is active and Load Cell 1 (I0.2) detects material, then Conveyor 1 Motor (Q0.1) turns ON.

Network 3: Conveyor 2 Activation

• When Load Cell 2 (I0.3) detects material (i.e., material has transferred from Conveyor 1 to Conveyor 2), then Conveyor 2 Motor (Q0.2) turns ON.

Network 4: Emergency Stop Logic

• If STOP Button (I0.1) is pressed, all outputs are turned OFF by resetting the Cycle ON (Q0.0) latch.

Functional Sequence (Interlocking Logic)

1. START Button Pressed (I0.0 = 1):

   • Q0.0 (Cycle ON) = 1

   • Q0.3 (Feeder Motor) = 1

2. Material Detected on Conveyor 1 (I0.2 = 1):

   • Q0.1 (Conveyor 1 Motor) = 1

3. Material Transferred to Conveyor 2 (I0.3 = 1):

   • Q0.2 (Conveyor 2 Motor) = 1

4. STOP Button Pressed (I0.1 = 1):

   • All outputs reset (Q0.0–Q0.3 = 0)

Runtime Test Cases

Inputs	Outputs	Physical Behavior
I0.0 = 1	Q0.0 = 1	Cycle ON Lamp turns ON
I0.2 = 1	Q0.1 = 1	Conveyor 1 Motor starts
I0.3 = 1	Q0.2 = 1	Conveyor 2 Motor starts
I0.1 = 1	All Q outputs = 0	System stops

Conclusion

This PLC program ensures automatic sequencing and interlocking of conveyor belts using load cell feedback. It minimizes manual intervention, improves reliability, and provides a robust material handling solution using Siemens S7-300 and TIA Portal.

Would you like me to also draw the ladder diagram or generate an image of the conveyor setup for better

 

Explanation of Motor Speed Initialisation Logic (Using First Scan Cycle, Initialisation Button, and Display Input)

Explanation of Motor Speed Initialisation Logic (Using First Scan Cycle, Initialisation Button, and Display Input)

This program controls how the motor speed value (MW10) is initialized and updated during PLC operation. It uses two special inputs—First Scan Cycle (I0.0) and Initialization Button (I0.1)—to determine when the system should load a default motor speed value. Under normal operation, motor speed is taken from the operator display (MW8).

Inputs and Memory Words Used

Signal / Memory	Description
I0.0	First Scan Cycle input (activates only once when PLC transitions to RUN mode)
I0.1	Initialization push-button (allows operator to reset motor speed)
MW8	Motor speed value coming from HMI or display
MW10	Final Motor Speed Word used by the PLC to control the motor

Ladder diagram for the first scan cycle.

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FBD diagram for the first scan cycle.

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Program Description

The main function of this program is to determine what value should be written into MW10 (Motor Speed) under different conditions:

A. Initialization Conditions (I0.0 or I0.1 active)

• If the First Scan Cycle (I0.0) turns ON
  OR

• If the Initialization Button (I0.1) is pressed

→ The PLC will load a default motor speed value of 10 into MW10.

This ensures that:

1. On PLC startup, the motor always begins with a known safe speed.

2. On operator demand, the motor speed can be reset to the same safe/default value.

B. Normal Operation (None of the initialization conditions active)

When neither I0.0 nor I0.1 is TRUE:

→ The motor speed is read from MW8 (HMI/Display Input) and written to MW10.

This allows the operator to modify motor speed from the HMI during normal running conditions.

Why This Logic Is Important

✔ Prevents unpredictable motor start-up values
✔ Ensures safety by assigning a known speed after startup or reset
✔ Allows operator control during normal running conditions
✔ Provides priority for first scan and reset operations

Final Explanation (Compact Version for Documentation)

This program ensures that MW10 (Motor Speed) is properly initialized and updated. During PLC startup or when the initialization button is pressed, the value 10 is moved into MW10. This sets a safe, predefined motor speed. If neither I0.0 nor I0.1 is active, the motor speed is taken from the operator display (MW8) and written into MW10. Thus, the logic provides automatic startup initialization and operator-controlled speed during normal operation.

Cyclical Program Execution 

In a Programmable Logic Controller (PLC), the logic written by the programmer does not run randomly or continuously by itself. Instead, the PLC follows a repetitive, continuous cycle known as the scan cycle or cyclical program execution. This cycle ensures that all input signals are read, processed by the logic, and the appropriate outputs are updated in a predictable and deterministic manner.

This concept is fundamental to understanding how PLCs behave and how control logic executes in real-time industrial systems.

What Is Cyclical Program Execution?

Cyclical program execution refers to the method by which a PLC constantly repeats a sequence of operations. The PLC reads all input values, executes the program, updates output signals, performs system tasks, and then starts again—continuously and cyclically.

This loop happens very fast, usually in milliseconds, ensuring the system responds to changes almost instantly.

The PLC Scan Cycle (Step-by-Step)

A standard PLC scan cycle consists of the following stages:

Step 1: Input Scan (Reading Inputs)

• The PLC reads the status of all input devices connected to digital or analog input modules.

• These include:

  • Sensors (proximity, limit switches, photoelectric)

  • Push-buttons (Start/Stop)

  • Analog sensors (temperature, pressure, flow)

• Input values are stored in a memory area called the Input Image Table (or simply Input Memory).

Key point:
PLC uses the stored input memory during the entire scan, not the real-time input state—inputs are locked in for that cycle.

Step 2: Program Execution (Logic Scan)

• The PLC executes the user program line-by-line, rung-by-rung.

• It uses the input values stored during the input scan.

• Instructions such as:

  • Contacts (XIC, XIO)

  • Coils (OTE)

  • Timers, counters, comparison

  • Mathematical and logical operations

• The results of the logic execution are stored in the Output Image Table (output memory), not directly written to the physical outputs yet.

Key point:
Outputs during execution are still virtual—they are not actuated until the next stage.

Step 3: Output Scan (Updating Physical Outputs)

• After executing the logic, the PLC updates the actual physical output modules.

• Output devices include:

  • Motors

  • Valves

  • Relays

  • Indicators

• The PLC writes the values from the Output Image Table to the output terminals.

Key point:
Only after this step do real devices respond to logic changes.

Step 4: Housekeeping and Communication Tasks

The PLC performs internal tasks such as:

• Diagnostics (checking module or CPU faults)

• Communication with HMI, SCADA, PCs

• Updating internal clock

• Memory management

• Background tasks, interruptions, high-priority operations

After completing these tasks, the PLC returns to Step 1 and repeats the cycle.

Why Cyclical Execution Is Important

✔️ Predictability and Determinism

Industrial systems need predictable timing. The scan cycle ensures consistent system behavior.

✔️ Fast Response

Scan times are typically 1–10 ms, ensuring real-time response.

✔️ Simplified Programming

Engineers can assume that logic executes in a consistent loop.

✔️ Reliable Automation

Input → Logic → Output happens in the same order for every scan, ensuring stable and safe operation.

Example of Cyclical Execution (Motor Control)

Consider a Start push-button (I0.0) and Motor (Q0.0):

1. Input Scan:
   PLC reads Start = 1 (pressed).

2. Logic Execution:
   Rung evaluates true → Motor coil (Q0.0) = 1.

3. Output Scan:
   Motor output physically turns ON.

4. Housekeeping:
   Communications with HMI updated, etc.

Next scan begins; even if Start is released, the latch holds Q0.0.

Factors Affecting Scan Time

• Program size (number of rungs, function blocks)

• Number of instructions (math, PID, communication-heavy)

• Amount of I/O

• Communication load (Modbus, EtherNet/IP, HMI, SCADA)

• CPU performance of the PLC

Scan time can be viewed in diagnostics tools in PLC software such as CCW.

Special Cases: Interrupts & Immediate Instructions

While PLCs normally follow cyclical scanning, some operations break this rule:

Immediate Input/Output Instructions

• Read/write physical I/O directly, bypassing scan tables.

Interrupt Routines

• Triggered by events such as:

  • High-speed counters

  • Communication triggers

  • Timed interrupts

• Run outside the normal cyclic scan.

These ensure high-speed or time-critical operations.

Summary

Cyclical program execution is the core method by which PLCs operate. Each scan cycle includes:

1. Input Scan – Read inputs

2. Program Execution – Execute logic

3. Output Scan – Update outputs

4. Housekeeping – System tasks

This predictable, repetitive cycle makes PLC-based automation stable, reliable, and responsive.

Types of automation topologies & Components of automation

Configuration of SITRANS TH300 in SIMATIC Manager

Description:

SITRANS TH 300 with HART protocol is designed to support all common thermocouples, resistance and milli-volt sensors

Setup is quick and easy with SIMATIC PDM

It works on DC voltage sources

Configuration of SITRANS P300 in SIMATIC Manager

Description:

It is a pressure measuring Instrument which is generally use for Absolute pressure measurement.

It can measure with accuracy ≤ 0.075%

It can work within limit of 1.3 bar pressure.

Silicon oil is used in Fluid filling in case in use of food industry edible oil is used because silicon is hazardous to human health.

 

Explanation:

First of all the mounting of instrument is done as per requirement.

When the pressure is applied in the valve of the instrument pressure is applied on Diaphragm so that it bends and piezoelectric plate is mounted on it.

When the piezoelectric plate bends the resistance is decrease in it so that when electric signal transmit on it difference can be shown on display that is measured pressure.

The readings in different units can be found using this instrument.

We can connect the equipment to the computer using PC/PD coupler and CP5711 via Profibus PA and Profibus PD can be analyzed on Simatic PDM. 

Schematic Diagram:

                                                                           

Configuration Steps:

Connect SITRANS P 300 to PC via Profibus and PC\PD Coupler.

Set the parameters of SITRANS P 300 using Mode button

Open SIMATIC PDM

File > New Project

View > Process Device Network View

Options > Set PG\PC interface [Select CP5711 Profibus 1<active>]

Project > Insert new object > Networks

Networks> Insert new object > Communication network > assign device type <Profibus network>

In profibus network Give the address of instrument i.e. 1-126 any number and assign instrument SITRANS P300

Open device > Open Project <upload \download to PG\PC>

Observe the result in process variable.

Conclusion:

Proper Commissioning of Device leads to accurate pressure measurement.

Position and Place of mounting is should be proper to get accurate output.

For Safety of the plant and workers this instrument is necessary.

We can conclude that by using this instrument we can maintain the pressure by setting higher and lower limit in equipment such as boiler, pressure vessel etc. and proper safety measures can be achieved.

                         
                                                                                                                 By Kartik Pandav