Powering the Phase Dock Trainer: A DigiKey Lab

Education
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This document is the first in a series of hands-on industrial control and automation experiments featuring relays and small Programmable Logic Controllers (PLC). In this installment, students prepare the Phase Dock 1010 base and an associated switch plate that will accept 22 mm switches and indicators. They install and then wire a DIN rail power distribution system featuring a compact 24-position Weidmüller terminal block. At the lab’s highlight students explore the limits of a bench type DC power supply along with the limits of the DIN rail mounted circuit breaker. A series of questions and critical thinking questions are included to reinforce the lab’s concepts.

Figure 1: Image of the Phase Dock 1010 trainer with DIN rail circuit breaker and power distribution block. The 24 VDC is provided by an external B&K Precision 1550 DC power supply.
Figure 1: Image of the Phase Dock 1010 trainer with DIN rail circuit breaker and power distribution block. The 24 VDC is provided by an external B&K Precision 1550 DC power supply.981×736 84 KB

Figure 1: Image of the Phase Dock 1010 trainer with DIN rail circuit breaker and power distribution block. The 24 VDC is provided by an external B&K Precision 1550 DC power supply.

Tech Tip: The designation of More Knowledgeable Other (MKO) is used throughout this lab to indicate the collaborative relationship between the learner and others who act as instructor, mentor, supervisor, coach, or even the advanced student familiar with the material. A good MKO knows when to provide assistance, when to let the student struggle with independent learning, and anchors the topics into a greater framework of learning.

Learning Objectives

The lab objectives include:

  • to construct DigiKey’s relay and small PLC trainer
  • use of hand tools to construct a physical assembly
  • to use DIN rail
  • to wire a circuit breaker
  • to wire a power distributions block
  • to operate a bench power supply in constant voltage and constant current modes
  • to observe and then differentiate a circuit breaker’s thermal trip from a magnetic trip

Measurable Assessment

Students will demonstrate mastery of the lab via these measurable assessment:

Assessment 1: MKO inspection of the assembly built as shown in the accompanying photographs. Hardware is not overtightened. DIN rail-mounted components have the proper orientation.

Assessment 2: Student can demonstrate the constant voltage and constant current modes of a bench power supply using a voltmeter. They can do so without assistance and without damaging the power supply or the meter (no blown fuses).

Assessment 3: Student can describe and demonstrate a circuit breaker’s thermal trip (delayed) and a magnetic trip (immediate).

Required Materials

The required materials are shown in Figure 2. A complete description of each component may be found in the Guide to Selecting Components for Industrial Education. The parts checklist for this portion of the project includes:

  • Common hand tools such as screwdriver, nut driver, wire cutter
  • DC power supply capable of 24 VDC at up to 2 A with ability to automatically shift between constant voltage and constant current mode
  • Phase Dock 1010 trainer
  • Phase Dock 4-position switch plate
  • DIN rail
  • Variety of pre-cut and ferruled wires
  • 2 ea terminal blocks
  • 1 ea end plate
  • 2 ea end stops
  • 6 ea hex standoff
  • 6 ea screw 8x32, ½ inch
  • 6 ea nylon screw

Tailgate / Toolbox Safety Brief

Before starting this lab, the student and MKO should conduct a tailgate briefing to review lab safety, objectives, and procedures. This checklist guides the conversation:

  • Ensure that the experiment is conducted using an isolated 24 VDC current limiting bench power supply. While this is generally considered safe, always turn off the power supply when making adjustments to the circuit.
  • Do not overtighten the Phase Dock hardware, as you will crack the acrylic base.
  • Review the operation of a circuit breaker including the specifications for AC and DC interruption.
  • Review circuit breaker tripping curves.
  • Review the characteristics of a circuit breaker’s magnetic and a thermal trip.
  • Review the operation of the bench power supply with a focus on the constant voltage and constant current functions.
  • Review DIN rail fundamentals including the concept of “this way up” with an introduction to the hook on top and latch on the bottom.
  • Review the operation of industrial screw and spring terminals.

Procedure

  1. Work with the MKO to construct the hardware assembly as shown in Figure 2. Be sure to include the screw-feet that came with the Phase Dock 1010 base to increase mechanical stability.

  2. Work with the MKO to install the DIN rail components as shown in Figure 3. Refer to First Steps for DIN Rail Hardware for additional information.

  3. Work with the MKO to operate the wire to spring connections on the Weidmüller terminal block.

  4. Wire the circuit breaker and power distribution block as shown in Figure 3.

  5. Work with the MKO to configure the external power supply to deliver 24 VDC with a current limit of 0.5 A.

  6. Demonstrate the power supply’s constant voltage and constant current modes using a voltmeter to measure voltage and current respectively.

  7. Turn off the circuit breaker.

  8. Short circuit the power distribution block by placing a wire directly between the 24 VDC and return.

  9. Turn on the circuit breaker and verify that the power supply has entered a constant current mode and is delivering 0.5 A.

  10. With stopwatch in hand, quickly ramp the power supply to 2 A and determine the time it takes to trip the circuit breaker.

  11. Compare the trip time to the Phoenix Contact TMC71C01A datasheet tripping curves

  12. With the power supply current limit still set at 2A, attempt to reactivate the circuit breaker. Verify that it trips immediately.

  13. Work with the MKO to complete the measurable assessments.

Figure 2: Completed Phase Dock base with DIN rail and a 4-position switch plate to accept 22 mm industrial pushbuttons and indicators.
Figure 2: Completed Phase Dock base with DIN rail and a 4-position switch plate to accept 22 mm industrial pushbuttons and indicators.927×695 60.4 KB

Figure 2: Completed Phase Dock base with DIN rail and a 4-position switch plate to accept 22 mm industrial pushbuttons and indicators.

Figure 3: Close up image showing the wire connections for the trainer’s DC power distribution. Blue wire is used for +24 VDC while white with blue stripe is used for the return.
Figure 3: Close up image showing the wire connections for the trainer’s DC power distribution. Blue wire is used for +24 VDC while white with blue stripe is used for the return.986×739 84.4 KB

Figure 3: Close up image showing the wire connections for the trainer’s DC power distribution. Blue wire is used for +24 VDC while white with blue stripe is used for the return.

Related Information

Please follow these links to related and useful information:

Follow up

Please reply using the button below if you have any questions about this DigiKey lab or the components used in this lab.

Questions

The following questions will help reinforce the content of the article.

  1. What is the purpose of the Phase Dock feet located underneath the acrylic base?

  2. What is a circuit breaker tripping curve? For full credit, identify the horizontal and the vertical axis.

  3. True / False: A 1 A circuit breaker will quickly trip when a 1 A load is applied.

  4. True / False: A 1 A circuit breaker may or may not trip when a 2 A load is suddenly applied. Provide a 1-word explanation.

  5. What color wire is used for 24 VDC and what color is used for return?

  6. Closely inspect Figure 1, is the system grounded or floating? Hint: Benchtop Power Supply Ground Connections

  7. Suppose the power supply’s delivered current was insufficient to trip the circuit breaker. Describe how this presents a safety hazard. For full credit use a residential circuit breaker as an example.

  8. Research and then describe the advantages and disadvantages of wire ferules.

  9. Research “thermal trip” and “magnetic trip” concepts as they apply to a circuit breaker. Use this knowledge to describe the observed operation of the circuit breaker. Specifically, why was it slow to trip when the 2A load was gradually applied but tripped immediately when the 2A load was suddenly applied.

Critical thinking questions

These critical thinking questions expand the article’s content allowing you to develop a big picture understanding of the material and its relationship to adjacent topics. They are often open ended, require research, and are best answered in essay form.

  1. Support or refute this statement, “It is criminally negligent to bypass or install an incorrect fuse into a voltmeter.”

  2. Research the grounding methods associated with the Class 2 power supply often used in industrial control panels. Are these systems grounded or floating? What are the advantages of each configuration?

  3. Research the wire color code used in industrial control panels. Which standard is being used for this trainer with blue for 24 VDC and white with blue stripe for return?

  4. Research and describe UL 508A. How does this standard relate to this trainer?

About this author

Aaron Dahlen, LCDR USCG (Ret.), is 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 further enhanced by 12 years of interwoven teaching experience. 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 instructed military technicians in the art of component-level equipment repair. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys bridging the gap between application and theory.