Measuring Resistance in a Circuit

This lesson explains how to measure resistance using the Microtrainer – Series and Parallel Circuit Trainer and a Fluke 15B+ multimeter. Resistance tells us how much a component restricts current flow, and learning to measure it correctly is a key part of electrical diagnostics.

What You Need

• Microtrainer board

• Fluke 15B+ or similar multimeter

• Leads connected to COM (black) and Ω port (red)

Understanding the Ω Setting

To measure resistance, switch your meter to the ohms (Ω) symbol.
This mode allows you to measure the resistance of components such as switches, wires, and resistors.

You may see OL on the screen.
This indicates:

• Over Limit / Overload

• The resistance is so high that the meter cannot register the value

• In most cases, this means an open circuit

Important Safety Step

Always disconnect the battery or power supply before measuring resistance.
Measuring resistance on a powered circuit provides false readings and can damage the meter.

Measuring Resistance on the Microtrainer

1. Measuring the Switch

• Set the meter to Ω

• With the switch OFF, the reading shows OL — very high resistance

• With the switch ON, the reading drops to about 0.5–0.6 Ω

• This low value indicates a good path (continuity)

A switch or wire should always have very low resistance when functioning properly.

2. Measuring a Fixed Resistor

The Microtrainer includes a 1 kΩ resistor.

Probing across it should display approximately 0.993 kΩ.
The k stands for kilo-ohms, which means:

• 1 kΩ = 1,000 ohms

Resistors have tolerance ranges, so a reading slightly above or below the printed value is normal.

3. Why LEDs Show OL

If you measure across the LED, the meter will show OL.
This is because LED resistance changes with applied voltage, and the LED requires forward voltage to conduct.
A separate video covers how LEDs behave with voltage and current.

4. Measuring the Resistance Blocks

The bottom section of the Microtrainer has resistors with different values and prefixes:

LabelMeaningExpected MeasurementmΩmilliohms (0.001 Ω)Very small; may not show accurately on basic meters1 Ωone ohm~1 Ω100 Ωone hundred ohms~100 Ω1 kΩone thousand ohms~1,000 Ω10 kΩten thousand ohms~10,000 Ω10 MΩten megaohms (10,000,000 Ω)~10 MΩ

Understanding the prefixes is essential when reading resistor values.

Series vs. Parallel Resistance

Series

When resistors are placed in series, the values add together.
Example from the board:

• Two 100 Ω resistors in series measure around 200 Ω

Parallel

When the same values are in parallel, the resistance decreases because current has two paths.
Example:

• Two 100 Ω resistors in parallel measure 50 Ω

A separate video explains this in more detail.

Key Takeaways

• Use the Ω symbol to measure resistance

• Disconnect power before testing

• Low resistance = good path

• OL = very high resistance (open circuit)

• Know your prefixes: Ω, kΩ, and MΩ

• Series adds resistance; parallel reduces it