Multimeters (Circuits for Beginners #4)

Summary

In this video, the presenter compares a benchtop multimeter with a handheld multimeter, explaining the key differences in functionality, design, and application. The benchtop model is larger, more expensive, and offers more precise measurements, while the handheld version is compact, cheaper, and simpler to use. The video covers how to properly measure voltage and current, emphasizing the importance of correct meter setup to avoid damaging the device. The presenter also highlights common mistakes when using multimeters and explains the significance of fuses and resistance for accurate measurements, all while demonstrating live examples and calculations.

Takeaways

• 😀 Benchtop multimeters are larger, more expensive, and offer more advanced features compared to handheld multimeters.
• 😀 Benchtop multimeters have multiple buttons, labels, and ports to measure different parameters like DC/AC voltage, DC/AC current, and resistance.
• 😀 Handheld multimeters are simpler, cheaper, and have a more compact design but with limited features and measurement capacity.
• 😀 Handheld multimeters usually feature three ports: COM (common), voltage/resistance/current, and a port for measuring higher current (10A max).
• 😀 It is essential to pay attention to current ratings to avoid blowing the fuse in a multimeter, especially for handheld models.
• 😀 For accurate voltage measurements, the multimeter should ideally have high resistance (almost infinite), so it doesn't affect the circuit.
• 😀 For current measurements, the ammeter needs to be inserted directly into the circuit path, as current flows through it like water through a pipe.
• 😀 A good ammeter should have very low resistance (close to zero) to minimize impact on the circuit while measuring current.
• 😀 A bad connection or incorrect setup, such as trying to measure current as if measuring voltage, can cause damage to the ammeter, often blowing the fuse.
• 😀 Benchtop multimeters tend to have smaller input resistance (or lower input impedance) compared to handheld models, making them more precise for sensitive measurements.
• 😀 A fuse blowing in a multimeter is often caused by improper current measurement setups, particularly when an ammeter is connected without breaking the circuit.

Q & A

What is the main difference between a benchtop multimeter and a handheld multimeter?

The main differences are size, price, and functionality. A benchtop multimeter is larger, more expensive, and often includes more advanced features, while a handheld multimeter is smaller, cheaper, and typically has fewer options.

What are the key symbols on a benchtop multimeter, and what do they represent?

The key symbols on a benchtop multimeter include: a straight line for DC voltage and current, a wavy line for AC voltage and current, the Omega symbol for resistance (Ohms), and a symbol for continuity check. Other buttons help in setting up the machine.

How does a handheld multimeter differ in its setup for measuring current compared to voltage or resistance?

A handheld multimeter has different ports for current and for voltage or resistance measurements. The current measurement ports typically have specific maximum current ratings, such as 400 mA or 10 A, with safety fuses in place to prevent damage from excessive current.

What happens when a current measurement exceeds the rated capacity of a handheld multimeter?

If the current measurement exceeds the rated capacity, such as 400 mA, the fuse inside the multimeter will blow, potentially damaging the device and interrupting the measurement.

What is the key distinction between measuring voltage and measuring current in a circuit?

When measuring voltage, the voltmeter is connected across two points without interrupting the current flow. For current measurement, an ammeter must be inserted into the circuit to break the current path and measure the flow.

How does the resistance of a voltmeter affect the circuit it's measuring?

A good voltmeter should have very high resistance, ideally infinite, to prevent it from affecting the circuit. If the resistance is too low, it can divert some current, potentially altering the voltage drop across other components.

What makes a good ammeter and how is it different from a voltmeter?

A good ammeter should have very low internal resistance (ideally 0 ohms) to allow current to flow freely through the circuit without significant resistance. In contrast, a voltmeter should have high internal resistance to avoid affecting the voltage measurement.

What would happen if an ammeter is incorrectly connected to a circuit?

If an ammeter is incorrectly connected, especially in parallel like a voltmeter, it can cause excessive current to flow through it due to its low internal resistance, potentially blowing the fuse inside the ammeter and damaging the device.

What is the role of fuses in multimeters and why are they important?

Fuses in multimeters protect the device from damage by breaking the circuit if the current exceeds the multimeter's maximum capacity. This prevents permanent damage to the internal components, such as in the case of excessive current measurement.

Why might there be a discrepancy between the current readings on a handheld multimeter and a benchtop multimeter?

The discrepancy could be due to a blown fuse in the benchtop multimeter. If the fuse is blown, the multimeter will not register the current correctly, while the handheld multimeter might still work properly, assuming it has not been overloaded.