Module 1: DC Fundamentals – Voltage, Current, Resistance & Circuits

Welcome, industrial automation technicians! This module is your essential starting point for understanding how DC electricity powers and controls the machines around you. We'll strip electricity down to its fundamental concepts, learning the language of circuits and the basic components that bring them to life. A solid grasp of these principles is crucial for effectively troubleshooting, maintaining, and even designing basic control systems.

Warm Up

Connect to to prior knowledge about atoms and a system that is similar to electricity.

Imagine a network of pipes carrying water.

• Current is like the amount of water flowing through the pipes at any given time. If a lot of water is rushing through, the current is high. If just a trickle is moving, the current is low. In electricity, current is the rate at which electric charge flows past a point, usually measured in amperes (A). So, more amps mean more charge flowing per second, just like more gallons per minute means more water flowing.

• Voltage is like the pressure pushing the water through the pipes. If there's a big difference in pressure between two points, the water will flow more forcefully. Similarly, voltage, also known as electric potential difference and measured in volts (V), is the "push" that causes electric charge to move. A higher voltage means a greater force pushing the electrons, like a steeper hill causing water to flow faster.

• Now, think about something that might make it harder for the water to flow through the pipes, like a narrow section or some gravel inside. This is similar to resistance in an electrical circuit. Resistance is the opposition to the flow of electric current, measured in ohms (Ω). A higher resistance means it's harder for the current to flow for a given voltage, just like a narrower pipe restricts the water flow even with the same pressure.

So, to recap the analogy:

• Water flow (gallons per minute) is like electric current (amperes).

• Water pressure (pounds per square inch) is like voltage (volts).

• Narrow pipes or obstructions are like electrical resistance (ohms).

This analogy helps visualize Ohm's Law, which states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance. In our water analogy, if you increase the pressure (voltage), you'll get more water flow (current), assuming the pipes (resistance) stay the same. If you make the pipes narrower (increase resistance) but keep the pressure the same, the water flow (current) will decrease. Mathematically, Ohm's Law is expressed as:

V=IR

Where:

• V is voltage (in volts)

• I is current (in amperes)

• R is resistance (in ohms)

Resources

Lab 1

Review Questions

Lab 2

Review Questions

Lab 3

Skill Assessment

Review Questions

Quiz/Skill Check

I. The Building Blocks of Electricity

Electricity, at its core, is the flow of tiny particles called electrons. However, in the industrial world, we often use a convention called conventional current flow. This convention simplifies circuit analysis and aligns with how many electrical diagrams and standards are presented.

• Conventional Current Flow: Imagine positive charges moving from the positive (+) terminal of a power source, through the circuit, and back to the negative (-) terminal. This is the direction we will use throughout this course for all our circuit analysis.

Let's define the fundamental concepts:

• Charge (Q): The Quantity of Electrons
  
  

  • What it is: The fundamental property of matter that causes it to experience a force when placed in an electromagnetic field. Think of it as the 'stuff' that moves.

  • Unit: The Coulomb (C). One Coulomb is approximately 6.24times10^18 electrons.

• Voltage (V): The Electrical "Push"
  
  

  • What it is: Also known as potential difference or electromotive force (EMF). Voltage is the energy per unit charge that causes current to flow. It's the "electrical pressure" or "push" in a circuit.

  • Analogy: Imagine a water tank. The higher the water level (potential energy), the more "push" it provides to the water flowing out. Voltage is like that water pressure.

  • Unit: The Volt (V).

• Current (I): The Rate of Flow
  
  

  • What it is: The rate at which electric charge (our conventional current) flows past a point in a circuit. It's the amount of charge moving per unit of time.

  • Analogy: In our water tank analogy, current is the amount of water flowing through the pipe per second.

  • Unit: The Ampere (A), often shortened to "Amp." One Ampere is one Coulomb per second.

• Resistance (R): The Opposition to Flow
  
  

  • What it is: The opposition a material offers to the flow of electric current. Materials that resist current flow are called resistors.

  • Analogy: In our water pipe analogy, resistance is like the narrowness of the pipe or friction within it, which restricts the water flow.

  • Unit: The Ohm (Omega).

II. Materials and Their Electrical Properties

Not all materials conduct electricity equally. We classify them into three main categories:

• A. Conductors
  
  

  • Description: Materials that allow electric current to flow easily because they have many "free" electrons that can move from atom to atom.

  • Examples: Copper (most common in wiring), Aluminum, Gold, Silver.

  • Industrial Relevance: Used for wiring, bus bars, and circuit traces where current needs to flow with minimal loss.

• B. Insulators
  
  

  • Description: Materials that strongly resist the flow of electric current. Their electrons are tightly bound to their atoms.

  • Examples: Rubber, Plastic, Glass, Ceramic, Air.

  • Industrial Relevance: Used for wire coatings, electrical enclosures, and to prevent unwanted current paths (short circuits).

• C. Semiconductors
  
  

  • Description: Materials with conductivity between that of a conductor and an insulator. Their conductivity can be controlled.

  • Examples: Silicon, Germanium.

  • Industrial Relevance: The foundation of modern electronics, including transistors, diodes, and microchips found in PLCs, sensors, and HMIs. (We'll cover these more in advanced courses, but it's important to know their fundamental nature).

Key Takeaways & Self-Check Questions

Key Takeaways:

• Electricity involves the flow of charge, driven by voltage, and opposed by resistance.

• We use conventional current flow (positive to negative) in industrial automation.

• Every circuit needs a source, a path, and a load.

• Understanding open, closed, and short circuits is fundamental for safety and troubleshooting.

• Learning circuit symbols is essential for reading schematics.

Self-Check Questions:

1. If you increase the voltage across a circuit, what generally happens to the current (assuming resistance stays the same)?

2. Which unit measures the "electrical pressure" in a circuit?

3. You are troubleshooting a simple circuit with a battery, a switch, and a lamp. The switch is closed, but the lamp is off, and you measure 0 Amps of current. What is the most likely state of the circuit?

4. Draw the schematic symbol for a resistor and a normally open (NO) pushbutton.

5. Why is a short circuit dangerous?

Quiz