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Allen-Bradley PLCs - A Hardware History

Allen-Bradley PLCs - A Hardware History

Credited with coining the name ‘PLC’, Allen-Bradley and parent company Rockwell Automation are major players in the world of control systems. Learn how the hardware platforms have evolved into the familiar modern configurations.


Understanding PLC Program Commands: Timers

Understanding PLC Program Commands: Timers

The timer is a fundamental function of ladder logic programming. In this article, we discuss on- and off-delay as well as retentive timers and define the inputs and outputs required to properly use them.


Power for Control Circuits: It’s Not Just Power Supplies

Power for Control Circuits: It’s Not Just Power Supplies

Power supplies tend to get a reputation as one of the most important power considerations of a DC control circuit - but we can’t ignore other key players: power filters, converters, and backup power modules.


Controlling Hydraulic Devices with Open and Closed Loop Systems

Controlling Hydraulic Devices with Open and Closed Loop Systems

What if you could control the end position and the speed of a hydraulic actuator accurately with just a simple signal? Some systems use simple open/close valves, but others require far more precision.


Variable Frequency Drives: Managing Network Outage Responses

Variable Frequency Drives: Managing Network Outage Responses

Even with the most reliable networks, network outages are inevitable for a host of reasons, and managing these outages in VFD systems becomes critically important.


How-To: Implementing a Data Highway Plus (DH+) System

How-To: Implementing a Data Highway Plus (DH+) System

Allen Bradley’s Data Highway Plus (DH+) networking ability is still found commonly in interfaces with legacy equipment. Understanding this network structure can bridge the gap between old and new systems.


Contactors versus Relays - Differences and Applications

Contactors versus Relays - Differences and Applications

Although the are similarities in operating theory, relays and contactors are used in industrial circuits for different specific applications, and should not be used interchangeably.


Hysteresis - Error and Compensation in Control Systems

Hysteresis - Error and Compensation in Control Systems

Hysteresis is a term introduced in basic control system courses and listed on sensor datasheets, but the terms is not often understood, with error deriving from both the system itself as well as the sensor.


Comparing Mechanical vs Hydraulic Forces

Comparing Mechanical vs Hydraulic Forces

In honor of May the 4th, Star Wars Day, we compare the sources and applications of the two most common force-delivery systems - mechanical and hydraulic.


Siemens SIMATIC PLCs - Hardware History

Siemens SIMATIC PLCs - Hardware History

In the first article of this series, we investigate Siemens as a major PLC manufacturer, learning about the hardware, software, and key applications of each product lineup.


Defining Scalar and Vector Control in VFD Outputs

Defining Scalar and Vector Control in VFD Outputs

Two common methods exist for driving induction motors with VFDs - linear scalar control, which is often labeled as V/f, and vector, or field-oriented control, which can be a bit more complex to understand.


Dynamic Braking Resistors for Motor Control Applications

Dynamic Braking Resistors for Motor Control Applications

Large DC and AC motor drives often provide terminals for installing a braking resistor. What are these resistors, and how do they slow down a machine? What hazards and cautions must be considered?


Introduction to Safety Relays

Introduction to Safety Relays

Redundancy and safety are often seen together in industrial safety systems. Safety relays monitor emergency devices to switch contacts based on status - but what makes them different from normal relays?


How-To: Programming with IO-Link Devices

How-To: Programming with IO-Link Devices

Advanced features such as programmable limits, diagnostics, and remote configuration are available with IO-Link devices. Learn how to connect an example IO-Link block into an actual PLC project.


Linear Position Sensors - Control is Only as Precise as the Feedback

Linear Position Sensors - Control is Only as Precise as the Feedback

Linear position sensors are used in electrical and fluid-actuated motion devices. They allow extremely precise position, velocity, and acceleration control, and provide feedback to ensure product quality and tolerance compliance.


Web-Based Industrial HMIs: What’s The Difference?

Web-Based Industrial HMIs: What’s The Difference?

With the increasing appearance of “web-based” HMIs, we investigate these devices, learn how they differ from the graphical HMIs, and see implications for our modern control system architecture.


DC Motors - Why Are We Still Using Them?

DC Motors - Why Are We Still Using Them?

AC motors are common throughout industry - easily controlled by VFDs and without the maintenance that comes with DC brushes. So then, why are DC motors still used in certain applications?


Info Byte: What’s the Deal With Debouncing Switches?

Info Byte: What’s the Deal With Debouncing Switches?

Before digital control systems, responses were fairly slow. Push a button, and a motor contactor engaged. These days, the speed of computers introduces some new challenges but brings solutions as well.


How-To: Building a PLC Project with Modbus Communication

How-To: Building a PLC Project with Modbus Communication

Modbus is a communication protocol stemming from the early days of Modicon PLCs, but is still common today. These two example implementations of Modbus transactions will get you started.


Info Byte: Preventing Relay Burnout with Flyback Diodes

Info Byte: Preventing Relay Burnout with Flyback Diodes

Inductive loads, such as solenoids and contactors, can cause arcs and failures back into electromechanical switching devices, causing costly downtime. The solution is cheaper than you think.