Behind every manufacturing process is an Industrial Control Panel.

Industrial control panels play a part in every aspect of your life. The device that you are reading this on was built in an automated assembly line. So was that glass holding your drink that you were reaching for. That food, even that delicious organic food, was touched by a manufacturing process on the way to your door. It has made people's lives better, expanding education to those who would otherwise have it, helping the elderly live independently, and has raised so many out of starvation and poverty.

Automation is a fascinating industry with so many aspects that it can be difficult to define just what it is because with the right combination of components, the possibility of what you can do is limitless. You can eliminate those dull, dirty and dangerous jobs. You can build cars and trucks, you can operate oil and gas refineries to fuel them, and assemble every accessory you could ever want for your car. You can analyze health trends, implement preventative measures to prevent long term problems, and develop assistive technology to help people adapt. And if you dream bigger, automation can put a person on the moon, put a rover on Mars, and send a probe into interstellar space.

With everything automation can do, it can leave you feeling that those gray boxes, the industrial control panels, are something that you can never understand. But the key is to understand the components inside of them and realize what you can do with each of them. Then it is simply a matter of selecting the right components for your application.

To the right is a guide to the devices on one of our PLC Trainers which is designed to get you familiar with the products you will encounter on a UL508A Industrial Control Panel. The following are very common terms that you will need to get familiar with.

PLC Programmable Logic Controller
Pilot Devices such as push buttons, selector switches, lights, potentiometers, and meters
HMI Human Machine Interface or Touchscreen
AC Drive or VFD Variable Frequency Drive and 3 Phase AC Induction Motor
Programming Software (not circled). Each device may have its own programming software such as Studio 5000 / RsLogix 5000, Connected Components Workbench CCW, etc
Sensors and IO Link which are called field devices
Motion Control, Linear Actuators, Pick and Place Systems, Gantries, Robots, and Cobots
Ethernet Switch

Below you will find a detailed description on each of these components.

PLC - Programmable Logic Controller. This is the brains of the machine. It collects information from the inputs of the machine and adjusts its outputs accordingly. There will be examples of inputs and outputs below but think of inputs as your eyes and your ears. Things that you use to observe our environment. And your voice would be an output because you use it to relay information based on what you see and hear. Notice how some items on your body are not clearly inputs or outputs. Take your fingers that you are touching the mouse with. You can use your finger to click the mouse button...an output...but you also can feel the mouse button with it...an input. Machines are the same way. Some items will be cut and dry whether it is either an input or output. Others will be a mix of both. You can program these in many different languages, the most common are Ladder Logic Diagrams, Function Block Diagrams, and Structured Text.

Push buttons, selector switches, lights, relays, variable switches, and meters. These are the basic items that you use to interact with the machine operator. Some are inputs so that the operator can tell the machine something and others are outputs so that the machine can tell the operator something. Some of these are digital or discrete or ON/OFF, binary, or simply a 0 or a 1. Others are variable or analog. You use analog when you wish to command or display some type of measurement. Examples of these devices can be found on the front and back of the PLC trainer with the label 2.

Digital Inputs and Outputs. These will be one of two values. ON or OFF. The type of contact determines when it is ON or OFF. A normally open contact (NO) means it is normally OFF and you will press the contact to turn it ON. A normally closed contact (NC) means it is normally ON and you will press the contact to turn it off

Push button. These are used to signal momentary commands and usually spring return when you release them.
Selector Switch. These come in many varieties but the most common two are 2 Position and 3 Position selectors.

2 Position Selector Switch. This will typically have one normally open (NO) contact block on it. When it is switched one way it will be ON and the other way it will be OFF.
3 Position Selector Switch. This will typically have two normally open (NO) contacts on it. When it is switched to the left one contact will close and the other will open, when it is switched to the right the opposite contact will close and the other will open, and in the middle neither contact will be closed.

Lights. These are used to signal to the operator the state of the machine. Is it running, is it in alarm, does it need a part loaded into it, etc. Sometimes these lights are combined into a stacklight where it can be mounted high for easy visibility.
Relay. These have many purposes. They can be used to signal between two systems that have incompatible voltages, switch loads that are higher amps than the pilot device contacts can handle, or switch loads that require multiple poles such as 3 phase motors. But they can also be used for basic machine logic. In fact, before the PLC, there were large cabinets of relays to sequence the steps of very complex processes such as assembling a car on an automotive assembly line.

Analog Inputs and Outputs. Sometimes we need more than a basic ON/OFF signal to make a decision. Examples of analog values are tank levels, distance, speed, volume, etc. Anything where you would need to measure something. Many of the devices described below are some variation of an analog signal. The following two are in label 2.

Potentiometer. These are used to vary a voltage signal. The most common one you have probably seen is a light dimmer. As you turn the dial, it varies the voltage to the light. In industrial applications, 0-10VDC is a common analog voltage signal.
Meter. A meter is a way to display a measured value. This meter will read a 4-20 mA or milliamp signal and display the value for you to read.

HMI - Human Machine Interface or Touchscreen. As control systems have become more complex, it has become necessary to relay more information to and from the machine operator. You can use the HMI for the same functions as the basic buttons and lights, but you can also display the actual alarm information instead of just illuminating a light, you can create trends (graphs) to display the performance of the machine, log data for data analysis, and send the information to the information network. Note that even though you can replace all your basic buttons and lights with an HMI, this is rarely done. Buttons are better for repetitive tasks and the operator can see a light from a much further distance than reading the status on an HMI. You will usually see them used together.

AC Drive or VFD Variable Frequency Drive and 3 Phase Drive. 3 Phase induction motors are the most common motors used in manufacturing. They are designed to run close to a speed based on the AC frequency or Hertz (HZ) that you apply to them. Many applications need to vary the motor speed and we use an AC drive or VFD to do this. The terms AC drive and VFD are used interchangeably. These drives can receive their speed command from an analog input, typically 0-10VDC or 4-20mA, or over a communications network such as Ethernet. While an AC drive can get the speed close to what you want, it is what we call open loop control which means it has no feedback to make sure that it is actually at the desired speed. To close the loop, you would use some feedback device such as the encoder described below.

Encoder. An encoder is used to measure position data. It could be a linear position or in the case of your PLC trainer, it is a rotary position. It is coupled to the 3 phase motor. It can measure both the rotary position and count how many revolutions it has made. Using this data, we can use the math instructions of the PLC to calculate the rate of how fast the motor is rotating. We can then compare this to the desired speed of the motor and adjust our speed command to correct any variations. This is called closed loop control. A very common way of doing this is with a PID Proportional Integral Derivative instruction. This is a very common equation used in process control to maintain a desired value. We go through this in depth in our PLC courses. Note while this may give us precision speed controls, this is not position controls. Look down at the Motion Control, Pick and Place, and Robots section.

Sensors and IO Link. These are the eyes of automated machines. In the early days, many machines ran based on timed logic and you “hoped” that everything worked correctly. As parts wore, the timing would have to be adjusted and many processes were not repetitive enough to successfully run based on time. This is where sensors come in. Basic sensors can check that a part is present or that a cylinder is in position. But as machines have evolved, so have the sensors. They can detect the type of material, the color, measure the part, and vision systems can examine parts for defects. As sensor technology has evolved, the way we collect data from sensors has as well. The most common way to collect sensor data is IO Link. This is a network that can collect basic sensor data such as if a switch is on or off, gather diagnostics information to let you know that you have a sensor failing, and even collect data from advanced devices such as the encoder above. Here are three basic sensors that you will commonly see

Photoelectric. This senses light. It can sense the presence of a part, tell you how far away the part is, or even tell you what color the part is.
Inductive Proximity. This senses materials that current can flow through such as steel, aluminum, brass, copper, etc.
Capacitive Proximity. While a crude definition, these sense items that electrons can agitate. While this obviously includes metal, it also includes you. Basically, non-insulated materials. What makes these great is that they can sense through insulated materials. The most common example is a sensor on the side of the tank to sense the water level.

Motion Control, Pick and Place Systems, Robots, and Cobot. These are used to do precise positioning. They may be a single axis linear actuator, two axis consisting of two linear actuators, a three axis gantry, a robot, or a cobot. They can all serve the same purpose depending on the application. You can use the to pick a part up and place it at the next station, reorient the part such as rotate it, or the part may stay in the same position and it may do some task on it such as applying glue, welding, machining, trimming, etc. A lot of people immediately think they need a robot or cobot when a basic pick and place actuator will do the job better. Start with the basic linear actuator. Once you understand it, the others are simply a combination of multiple actuators.

Ethernet Network. There are many industrial networks including Controlnet, Devicenet, Profibus, DH-485, etc but the most common one is Ethernet. It can run many protocols, Ethernet/IP, Profinet, and Modbus TCP are the ones to learn about first. You will use these to connect your devices together to the PLC and send data on to your office network or the cloud.

Other common industrial items that were not labeled on the picture

Enclosure or Panel. This is the “gray box” that all the components go in. They are not always gray but it consist of two parts. The enclosure is the “box” and the panel is the plate inside of it that all of the components are mounted to.

Disconnect. These are used to deenergize the main power coming into your panel. Common types are main breakers, fuses, and non-fused. There will then be some type of linkage that connects it to the outside of the door so that the power can be turned off without opening the enclosure.

Transformer. Transformers are used to convert one AC voltage to another AC voltage. Common main powers are 480VAC and 240VAC. Typically you would connect these to the primary of the transformer. 120VAC and 24VAC are common values that you want to get out of a transformer. You would wire these to the secondary.

24VDC Power Supply. This converts AC to DC or DC to DC. 24VDC is the most common control voltages but 5VDC may be used on high speed devices such as encoders.

Motor Starters. A motor starter is an assemble of a contactor (big relay), and some type of overcurrent protection (overload or Manual Motor Starter MMS). Some motors need to reverse direction, these would have two contactors.

DIN Rail. This is the universal mounting material for most lightweight control components. It stands for Deutsche Institut für Normung but don’t worry about memorizing that acronym. Most people with 30 years of experience don’t know what it stands for.

Wire Duct. Wire duct, sometimes called cable duct, is used to conceal the wires as they are routed through the control panel.

Terminal Blocks. Terminal blocks are used to make connections between wires in a control panel. Where in an electrical box, you may use a wire nut, in a control panel, we use these. There is a tremendous variety of these to make your panel building go smooth.

Wire Labels. Labeling is incredibly important when it comes to making sure you don’t make mistakes when building a control panel and for troubleshooting problems later. Every panel needs labels.

UL 508A. UL is one of several Nationally Recognized Testing Laboratories (NRTL). OSHA 1910 requires that control panels be certified by one of these NRTLs. This is NOT optional, even if you are building a control panel in house. This most common one is UL 508A

SCCR. The Short Circuit Current Rating is the maximum current a device or system can safely withstand for a specified amount of time or until a protective device such as a circuit breaker of fuse opens. This is not the same as the fuse or circuit breaker rating and is usually in kA or kiloamps.

Enclosure Ratings. This is an environmental rating or how much protection the enclosure gives the components inside against dust, moisture, water, and chemicals.