Inst ToolsInst ToolsInst Tools
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Erection & Commissioning
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
  • Request
Search
  • Books
  • Software
  • Projects
  • Process
  • Tools
  • Basics
  • Formula
  • Power Plant
  • Root Cause Analysis
  • Electrical Basics
  • Animation
  • Standards
  • 4-20 mA Course
  • Siemens PLC Course
Reading: Safety Considerations in PLC System Design
Share
Font ResizerAa
Inst ToolsInst Tools
Font ResizerAa
  • Courses
  • Design
  • PLC
  • Interview
  • Control System
Search
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Erection & Commissioning
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
  • Request
Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Inst Tools > Blog > PLC Tutorials > Safety Considerations in PLC System Design

Safety Considerations in PLC System Design

In this article, we will learn the safety considerations in a PLC system design such as power supply, earthing, interlocks, alarms, etc.

Last updated: August 27, 2023 2:29 pm
Viral Nagda
PLC Tutorials
No Comments
Share
6 Min Read
SHARE

PLC is a very important part of industrial automation. It is the base of automation and every PLC programmer or automation engineer must design it properly so that it works properly. It is not just about programming, but ultimately how you design the PLC system.

Contents
Safety Considerations in PLC System DesignPower SupplyEarthingCritical Digital Input SignalsManual Mode InterlocksAlarms

Safety Considerations in PLC System Design

Safety Considerations in PLC System Design

We all think that if write a program properly with all the interlocks, sequence, and flow properly, then our PLC system is ready to use. But, it must be noted that one of the most important parameters in designing any system is safety. So, similarly, a PLC system must be designed considering safety in mind. In this article, we will learn the safety considerations when designing a PLC system.

Power Supply

This is the first and foremost parameter in considering PLC design. There are two types of power supplies in the panel – DC and AC. DC is usually 12-24V DC and AC is usually 110V AC or 230V AC.

PLC is powered up by either of the supplies and the field instruments too are powered up by either of the supplies. If a panel has a single SMPS or 230V single bus bar, then it becomes easy for designers to wire the system. If a panel has multiple power supplies, then there are chances that you will connect a positive wire from one supply and a negative wire from another supply by mistake. This will instead complex your system and make troubleshooting harder. So, a single power supply also minimizes line interference and prevents faulty input signals coming from a stable AC source to the power supply and CPU.

Multiple power supplies are unwanted and also create more chances of short circuits and frequent breakdowns. So, power supply design is a very important factor for safely operating the PLC system.

Earthing

Earthing, as we all know, is required to pass any leakage current to the ground. This prevents electric shock, noise, and electromagnetic interference. The standard neutral to earthing voltage must be less than 0.5V in industrial areas.

A slightly higher side of 1V is acceptable, but if it is above that, then it means the earthing is not proper and leakage happening in electrical signals will hamper the performance. PLC power supply, and IO channels, must be properly grounded and connected to the earth bus bar in the panel.

Also, instrument earthing and power earthing must be separate; otherwise, any merge in the earthing will create short circuits or interference in signals.

Critical Digital Input Signals

Every PLC system must have critical inputs like emergency stop, panel power failure, and air pressure. Also, all these signals must be connected in NC (normally closed) format.

The emergency stop is used to stop the system suddenly when an operator presses this button, panel power failure is used to stop the system when there is any problem in the phase power supply, and the air pressure signal denotes whether air is required to operate valves or other pneumatic outputs is proper or not.

All actions should stop immediately if any of these inputs fail. In some large systems, it is also observed that if the emergency is pressed, then instead of stopping the whole system, provide an emergency stop for individual large rating outputs. Due to this, the operator can isolate every system easily and operate other systems instead of stopping the whole system.

Manual Mode Interlocks

Programmers always take manual mode logic lightly. Just turning on or off the outputs is their motive. However, it must be noted that any irregular operation of outputs manually can hamper the system’s performance. If the system is very critical, then it can cause life-threatening issues to the personnel nearby.

So, it is recommended to apply alarms or other critical interlocks in manual mode too. This prevents the operator from operating the system randomly. Also, the safety of the PLC system is ensured due to this logic.

Alarms

All alarms given in a control logic document are usually taken by the programmers in the program. However, PLC programmers must provide some additional safety alarms in the system, according to IO’s taken in the PLC.

These are usually run feedback alarms, trip feedback alarms, over or under travel alarms, sensor failure alarms, PLC channel failure alarms, thermal overload alarms, thermostat alarms, over or under voltage alarms, etc. These alarms vary from system to system, based on the actual inputs taken.

But, if any of these inputs are not there, then it is recommended that programmers suggest the same to customers for considering them. This prevents the system from operating in a malfunctioning way.

In this way, we saw some general safety considerations when designing a PLC system.

If you liked this article, then please subscribe to our YouTube Channel for Instrumentation, Electrical, PLC, and SCADA video tutorials.

You can also follow us on Facebook and Twitter to receive daily updates.

Read Next:

  • Motor Faceplate in Graphics
  • HMI and VFD Control System
  • Update PLC Firmware Version
  • PLC Sorting Machine System
  • PID Controller Control System
Don't Miss Our Updates
Be the first to get exclusive content straight to your email.
We promise not to spam you. You can unsubscribe at any time.
Invalid email address
You've successfully subscribed !

Continue Reading

PLC Programming Example on Multi-Motor Control for Beginners
Sorting & Distribution Line PLC Programming – Advanced Logic
PLC Ladder Logic Example
Single-acting Pneumatic Cylinder Operation with Limit Switch
PID Controller Output Types – PID_PWM and PID_Output
How to Solve Electrical Ground Loop Problems?
Share This Article
Facebook Whatsapp Whatsapp LinkedIn Copy Link
Share
Leave a Comment

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Stay Connected

128.3kFollowersLike
69.1kFollowersFollow
210kSubscribersSubscribe
38kFollowersFollow

Categories

Explore More

PLC Ladder Logic Example based on Set Coil and Reset Coil
PLC Motor Logic with START, STOP, TEST Push buttons
Wiring Diagrams of PLC and DCS Systems – DI, DO, AI, AO
PLC Programming Example on LED Control
Ladder Diagram Example using Memory Bits and Set Coils
Difference between Signal Cables and Control Cables
How to Read the PLC Datasheet? – Important Notes About PLC
PLC Program for Positive Edge Pulse Output for One Scan Cycle

Keep Learning

Simple Conveyor Control PLC Program

XG5000 Example of Simple Conveyor Control PLC Program

Automatic Car Washing Process using PLC Ladder Diagram

Automatic Car Washing using PLC

PLC program Permissive Circuit

PLC Electric Motor Interlocks

4-20mA Current Loop Components

Why Use a Current Loop?

In this article, we will learn the difference between Machine Expert Basic and Machine Expert software in Schneider PLC.

Difference between Machine Expert Basic and Machine Expert – Schneider PLC

Delete Siemens CPU Memory

How to Delete the Siemens CPU Memory?

Automatic Lamp Control in Storage Facility

PLC Program for Automatic Lamp Control in Storage Facility

PLC Program for Automatic Oil and Water Separation Process

Oil and Water Separation Process using PLC Programming

Learn More

Why Grounding

Generating Station Grounding Principles

Instrumentation loop Diagram

Instrumentation Loop Diagrams

Critical Factors to Consider for Engineering Students to Ensure a Smooth Path

Critical Factors to Consider for Engineering Students to Ensure a Smooth Path

Controlling of Tank Level Using Proportional Controller in PLC

Controlling of Tank Level Using Proportional Controller in PLC

What is Poppet Valve?

What is Poppet Valve? When we Use a Poppet Valve?

Types of Interrupts Organization Blocks in Tia Portal

Types of Interrupt OB in Siemens Tia Portal

Power System Protection Quiz

Electrical Power System Protection Quiz

What is a Time Delay Relay

What is a Time Delay Relay? Principle, Advantages, Disadvantages

Menu

  • About
  • Privacy Policy
  • Copyright

Quick Links

  • Learn PLC
  • Helping Hand
  • Part Time Job

YouTube Subscribe

Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Welcome Back!

Sign in to your account

Username or Email Address
Password

Lost your password?