The importance of selecting high- vs low-impedance multimeters

[ruxton.stanislaw]

The choice between a high-impedance and low-impedance multimeter depends on the specific application you're working on. Here's a breakdown of the importance of each type to help you decide:

High-Impedance Multimeter:

• High Input Impedance: This means the meter draws very little current when measuring voltage. This is crucial when measuring circuits with high resistance, like logic circuits or amplifiers. Even a small amount of current drawn by the meter can alter the voltage being measured in high impedance circuits.
• Advantages:
  • Accurate Voltage Measurements in High Impedance Circuits: Minimizes the impact of the meter on the circuit being measured.
  • Safe for Sensitive Circuits: Low current draw prevents damage to delicate electronic components.
  • Wide Range of Applications: Suitable for measuring voltage in various circuits, including digital electronics, batteries, and sensors.
• Disadvantages:
  • May Not Be Ideal for Low Voltage Measurements: High impedance can lead to inaccurate readings on low voltage circuits due to voltage drops within the meter itself.
  • Susceptible to Ghost Voltages: Stray electrical fields or poorly shielded cables can induce small voltages that the meter might pick up, leading to false readings.

Low-Impedance Multimeter:

• Low Input Impedance: Draws a higher current compared to a high-impedance meter. This can be beneficial in some scenarios.
• Advantages:
  • Better for Low Voltage Measurements: The lower current draw helps to minimize voltage drops within the meter, leading to more accurate readings in low voltage circuits.
  • Can "Load" Circuits: The current drawn by the meter can be used to test how a circuit behaves under load. This can be helpful for troubleshooting purposes.
  • Less Prone to Ghost Voltages: Lower impedance is less susceptible to picking up stray electrical fields compared to a high-impedance meter.
• Disadvantages:
  • Can Alter High Impedance Circuits: The current drawn by the meter can affect the voltage in high impedance circuits, leading to inaccurate readings.
  • May Not Be Safe for Sensitive Electronics: Excessive current draw can potentially damage delicate components.

Choosing the Right Multimeter:
Here are some guidelines to consider:

• Circuit Type:
  • For high impedance circuits (logic circuits, amplifiers): Choose a high-impedance multimeter.
  • For low voltage circuits or circuits where you want to test under load: Consider a low-impedance multimeter (use caution with sensitive components).
• Measurement Range: If you'll be working with a wide range of voltages, a high-impedance multimeter with a good low voltage measurement range might be the best option.
• Additional Features: Some multimeters offer switchable input impedance or have features that help minimize the impact of the meter itself on the circuit being measured.

Remember:
The best multimeter for you depends on your specific needs and the types of circuits you'll be working on. Consider the factors mentioned above to make an informed decision.

 

[LarryFine]

I use a solenoid tester (Knopp K60) for 99% of troubleshooting because it eliminates phantom voltages.

I only use a voltmeter when I need to know the specific voltage, and make sure it's while under load.