When it comes to the right tool for testing and troubleshooting, when should you choose an oscilloscope and when should you reach for multimeter? Comtest, local distributors of Fluke, which makes both types of instruments, sheds some light on the subject.
THE difference between an oscilloscope and a digital multimeter is simply stated as “pictures vs numbers”.
A digital multimeter is a tool for making precise measurements of discrete signals, enabling readings of up to eight digits of resolution for the voltage, current, or resistance of a signal. An oscilloscope is designed to visually depict waveforms to show signal strength, wave shape, and the value of a signal. But how does the difference between numbers and pictures translate to real-world testing or troubleshooting?
Why use a digital multimeter?
Handheld digital multimeters typically have 3.5 to 4.5 digits of resolution and good accuracy. They are portable and lightweight, used typically for front-line testing and general-purpose measurements. They also contain advanced functions for special-purpose testing, such as fast
- Min/max
- Conductance
- Relative reference
- Duty cycle/pulse width
Logging
You can also find high-accuracy (5 to 8 digits resolution), bench-type, line-powered digital multimeters that are not intended for field use. These digital multimeters are used in the lab, mostly for research and development or for production systems. An advanced bench precision digital multimeter can cost as much as a portable oscilloscope.
Why use an oscilloscope?
Oscilloscopes are designed for engineering work or troubleshooting systems that might contain complex signals that send at speeds much faster than a digital multimeter can capture. Scopes have much faster measurement engines and much wider measurement bandwidths than digital multimeters, but typically do not have the same accuracy and resolution strength as a multimeter. Oscilloscopes generally have a resolution equivalent to a 3.5-to-4-digit digital multimeter.
One of the advantages of an oscilloscope over multimeter is that oscilloscopes also have the ability to visually display complex signals (the “picture” part in the adage), able to show a transient signal that may pose a threat to a system can be displayed, measured, and isolated with an oscilloscope. It will also graphically show distortion and noise that may be present in the signal.
Oscilloscopes can be line powered or battery powered; they can be big or small. Battery power and smaller size, for portability, are typically required for field use. Some oscilloscopes have built-in multimeters like the Fluke 120B ScopeMeter, giving you both numbers and pictures. In many cases, these kinds of oscilloscopes can replace a multimeter.
Oscilloscope vs Multimeter
Make sure to keep your digital multimeter with you for any electrical work. Grab one to make high-precision checks of voltage, current, resistance, frequency, and other electrical parameters. If a red flag is raised with your multimeter, you may need to grab an oscilloscope or more powerful tool to diagnose further.
Reach for an oscilloscope if you want to make both quantitative and qualitative measurements. For general-purpose maintenance or general electronic testing, a digital multimeter is fine, but when testing or troubleshooting machine controls or other complex systems, or doing electronic design work, an oscilloscope is needed.
- Industrial electronic applications like automation and process control: an oscilloscope with two isolated inputs and 60 MHz, 100 MHz, or 200 MHz bandwidth is the choice.
- Industrial machine applications measuring three-phase power electronics, or three-axis control systems comparing and contrasting multiple signals: an oscilloscope with four isolated input channels and 100 MHz or 200 MHz bandwidth is ideal.
- Industrial network applications: some oscilloscopes add industrial network physical layer analog measurement algorithms to validate the network health.
