Guide to Selecting Industrial Component for Education

This page provides supports a larger topic involving trainer for relays and small PLC.

How do we select industrial components for a PLC and relay trainer?

This document identifies components appropriate for a first course in relay control and Programmable Logic Controllers (PLCs) suitable for electrical and mechanical technicians and engineers. This is a continuation of the industrial control relay and small PLC trainer. We have attempted to remain supplier neutral. However, you the educator, require a specific list to build out your shopping cart. This cannot be resolved without selecting specific components from specific suppliers. To resolve this dichotomy, please consider these high-level overall objectives:

  • Safety: Components are designed to work within a 24VDC system ensuring general safety for your students. An external bench type power supply provides current limiting.

  • Cost: These are not necessarily the lowest cost components, but components that are designed to work well together to maximize the educational experience.

  • Educational experience: The components are chosen to be student friendly. As an example, consider the Altech momentary pushbuttons shown in Figure 1. These switches are highly modular and easy to assemble. The clear markings and color are especially useful for students as they learn to distinguish the difference between normally open (green) and normally closed (red) switch blocks. Another education-based decision is found in the chosen relays. Students will encounter a variety of relays with regards to wire connections, freewheeling diode, and a variety of forcing mechanisms.

  • Enhanced experiments We have included additional sections for PLC selection and other components such as a motor starter to enhance the learning experience. Selection of a PLC is a complex multifaceted exercise. This section is expanded to explore some of the selection decisions.

You are encouraged to review the list and mix and match to meet your educational needs. As a starting point, we have identified the component and offered a specific example.

Please refer to this page for additional education contact pertaining to many of the devices featured in this list.

Figure 1: Components such as these 22 mm pushbuttons are immediately identifiable as normally open or normally closed by virtue of their green and red color respectively.

Tech Tip: The components listed on this page may be reused in capstone projects for electrical and mechanical technicians / engineers. Be sure to inventory your classroom kit to ensure the components find their way back at the end of the semester.

Core components

This section contains a core selection of components for industrial control and automation students. It begins with the core of the trainer and then identifies DIN rail mounted components along with 22 mm switch and panel indicators.

Trainer base and hardware

  • 1 ea Phase Dock 1010 workbench base
  • 1 ea Phase Dock 1010 Switch Plate featuring 4 ea 22 mm holes for panel mount switches and indicators
  • 1 ea American Electrical TS3575SL steel DIN rai cut to 9 inch length
  • 6 ea Keystone 2221 hex standoff
  • 25 ea Keystone 9907 1/2 inch 8-32 Phillips machine screw
  • 10 ea Keystone 9603 hex nut
  • 25 ea Keystone 3363 nylon flat washer
  • 6 ea Essentra 090832050TB nylon thumbscrew

Power block and circuit beaker

  • 1 ea Weidmüller 2506340000 power distribution block
  • 1 ea Phoenix Contact 1019972 Circuit breaker 1A

Terminal block and associated material


  • 3 ea Altech S1 normally open switch body
  • 2 ea Altech S2 normally closed switch body
  • 2 ea Altech 2AF4 red pushbutton, momentary
  • 2 ea Altech 2AF3 green pushbutton, momentary
  • 1 ea Altech 2AS2-1 selector switch, On-Off maintained


  • 1 ea Phoenix Contact 2903350 DPDT relay (spring terminal)
  • 1 ea Phoenix Contact 2905291 DPDT (spring terminal) relay with integral flyback diode and test lever
  • 1 ea Finder Relays 58.P4.9.024.0050SPA 4PDT relay (spring terminal)
  • 1 ea Selec Controls 600XU-A-1-CU-ROHS multifunction relay

Panel lights


  • 1 ea Alpha Wire 3053 BL005 blue 100- foot spool
  • 1 ea Alpha Wire 3053 WU005 white with blue stripe 100-foot spool

Power supply

An external 24 VDC power supply is required. The typical electronics lab is already equipped with a benchtop power supply.

Programmable Logic Controller (PLC)

The trainer is ideal for introducing relays as well as small PLC. It’s difficult to select a specific PLC as there are many options, each with unique capabilities and programming environment. As you select a PLC please consider these attributes:

  • Ladder logic programming is recommended for a student’s first PLC experience. This is an important consideration to reinforce the hardware (relay) based thought process with the software equivalent. There is also an argument for the enduring importance of ladder logic.

  • Select a PLC that is popular with manufacturers in your area therefor providing your students with job ready skills. This is a good conversation to have with your industrial advisory board.

  • It is difficult to identify a single “best” PLC for an academic setting as there are so many options. However, as a starting point please consider:

    • Arduino: The Arduino Opta is a relatively new option offered as part of the Arduino PORTENTA Pro product line. The Opta has unique advantage from a programming perspective as it may be programmed using the traditional Arduino C++ dialect as well as all of the IEC 61131-3 languages. Consequently, the learner may ease into industrial control applications by leveraging their prior Arduino experience.

    • Schneider Electric: PLCs such as the Modicon nano TM221CE16T are new product to the DigiKey line. The TM221CE16T PLC features semiconductor (sourcing) outputs which will enhance learning by forcing students to use interposing relays to drive larger loads. Also, the PLC may be programmed in the following IEC 61131-3: Ladder Diagram, Instruction List, Grafcet (List), and Grafcet (SFC).

    • Siemens: The LOGO! PLC family offers many options. Devices such as the 6ED10521MD080BA2 feature a built-in character display and pushbuttons. A variety of expansion modules are also available. The LOGO! is programmed using LOGO! Soft Confort which is dialect of function block.

    • Crouzet: The Millenium Slim is one of the physically smallest devices in the DigiKey line. This particular device features solid state (sourcing) outputs. It is programmed using a combination of function block and sequential function chart. The Millenium Slim may be configured to you a cell phone as the Human Machine Interface (HMI).

    • Phoenix Contact: The Smart Programmable Relay provides a unique introduction to programmable logic by combining PLC module that plugs into discrete relays. The result is a flexible compact system that may eliminate the need for terminal blocks. The system is graphically programmed.

    • Other: DigiKey offer other introductory PLC and programmable relays that may be if interest including those by Altech, Delta IDEC, Panasonic, Selec, Sfera, and others. Please see this link for the lasted update as DigiKey adds additional products.

Please leave comments in the space below if you have question about selecting a PLC to meet your specific needs.

Wire Ferrules

Items such as wire and associated ferrules are considered consumables. There is a balance between using pre-cut / ferruled wires and the need to cut wires to specific length. The construction philosophy of this engineering brief emphasizes ease of connection over neatness; this is why there is no wire duct on the trainer. However, all students must develop the skill of measuring wire to the proper length and attaching single as well as twin ferrules.


  • 100 ea Weidmüller 9019400000 Ferrule Connector Single Wire
  • 100 ea Weidmüller 9037200000 Ferrule Connector Two Wire
  • 1 ea Hand Crimper for ferrules; Weidmüller 1445070000

Tech Tip: The ferrule crip tool is the single most expensive component on this page. It is important to match the crip tool to the chosen ferrules as outlined in this article. While not strictly necessary from an education perspective, this match-to-manufacturer-specifications is a fundamental requirement for a UL 508A certified panel shop. To save cost, it may be beneficial to purchase one crimp tool for your lab. You can use the tool to construct pre-cut wires. Then, on an individual bases, students can use the crimp tool for custom wire lengths and twin ferrules connections.

Components to enhance learning

The previously mentioned components will facilitate a solid introduction to relay-based control systems along with introductory PLC programming. From this point forward there are many learning opportunities. However, all students would benefit from an expanded understanding of the magnetic motor starter and an expanded understanding of common commonly used panel components.

Motor Starter

  • 2ea Schneider DPE09BL 3-phase contactor
  • 1ea Schneider DPER06 thermal overload block adjustable 1 to 1.7 A
  • 1ea Schneider DPEAN11 auxiliary contact block

Lights and Switch



  • 1 ea Panasonic GX-F12A-P inductive proximity sensor
  • 1 ea Carlo Gavazzi CD50CNF10PO capacitive proximity sensor

Next Steps and additional resources

DigiKey continues to expand a list of associated training material. Here are a few examples for your consideration. These pages are written as freestanding education materials. Some pages contain a list of questions to enhance student learning.

Be sure to visit the Industrial Control and Automation Index. DigiKey continues to the number and scope of the education content.

Parting thoughts

This document presents a cohesive collection of parts suitable for the relay and small PLC trainer described in this article.

Your feedback is most welcomed. For example, do you have a preferred set of classroom components? We are especially interested in any classroom challenges associated with general electronics or industrial control and automation.

Best Wishes,


Return to the Industrial Control and Automation Index.

About the author

Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (interwoven). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing articles such as this. LinkedIn | Aaron Dahlen - Application Engineer - DigiKey