How to use a digital multimeter





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Published on Oct 5, 2011

Tony and Ian from Tektronix explain what is a digital multimeter, how to use a digital multimeter, and other digital multimeter basics, using a simple DC Circuit example.

What is a Digital Multimeter?
At its heart, a digital multimeter is a device that measures voltage, current, and resistance. Those are the basics, but modern digital multimeters can measure other things as well. Some digital multimeters can measure power and frequency, and some can make different kinds of measurements at the same time.

How to use a Digital Multimeter
Take an example of a simple DC circuit: just a battery and a couple of resistors. The resistors are marked the same, so they should have similar resistance. That means the voltage drop across the two should be about the same. With a 1.5V battery, expect the voltage across each resistor to be roughly half that: about 0.75V.

You can use a digital multimeter to measure voltage and compare resistance:

Measure Voltage
By adding a probe you can measure the voltage across each resistor and use your digital multimeter to see if the voltage really is the same. In the example shown, the voltages are close, but not identical. Having the digital display really helps you to see exactly what the voltage is. Also, if there is a difference in voltage, what the difference is. This is a big advantage of a digital multimeter over an analog multimeter.

Compare Resistance
A digital multimeter can measure resistance as well. You can put the digital multimeter into resistance mode and measure the resistance directly.

Digital Multimeter Basics
A digital multimeter has inputs where you connect your probes, a readout where you see the measurement results, and buttons to select the measurement type and range.

Here's a summary of each basic element:

Main Measurement Types
The featured digital multimeter supports several different measurements. The five main measurement types are: DC voltage, AC voltage, DC current, AC current, and resistance. Each measurement has its own units and range. Some measurements also have their own completely different connectors on the front panel.

The two inputs that are most commonly used are for voltage and simple resistance measurements. If you're measuring current, you'll use a completely different input for the high probe. This is because current measurement is fundamentally different from voltage or resistance: you're breaking the circuit. There are actually two different current inputs, depending on the maximum current you're measuring. It's important to use the correct connectors for your measurement.

Working with Ranges
The Digital Multimeter will measure up to 1000V. Digital multimeters don't just have just one single range because the number of digits of resolution you need depends on what you're measuring. If you're looking at a 100mV signal on a circuit board, you may need to know the voltage to the nearest microvolt. But if you're looking at something in the hundreds of volts (with safety precautions!), then you may only care about the nearest tenth or hundredth of a volt.

The featured digital multimeter supports ranges of 0.1V, 1V, 10V, 100V, and 1000V. You typically want the range to be the closest voltage above the signal you're measuring. So if you're looking at a circuit powered by a 9V battery, you could set the range to 10V (most digital multimeters will do this for you). All you have to do is put your digital multimeter into auto-range mode, and it will automatically select the voltage range based on the signal you're feeding into it.

If the digital multimeter sets the range automatically, why would someone use the manual range? If your signal is right at the boundary between one range and the next, and the digital multimeter keeps hopping back and forth between the two ranges, you'd probably want to put it in manual mode and just pick a range.

What is Zeroing?
All electronic components drift slightly over time and temperature changes. The components inside a digital multimeter are no exception. Zeroing is a way to adjust the digital multimeter to these changes. It also helps compensate for the resistance of the probe leads. To zero your digital multimeter, just apply an input of zero volts or ohms (depending on the mode you're in), and press the Zero button.

The Importance of Safety
The safe use of equipment is important. Using the wrong inputs for a signal, or applying a much higher signal than the device is rated for, can blow fuses, damage equipment, and endanger your safety. Please read the safety section of your digital multimeter manual before connecting any inputs to it.

For more digital multimeter tutorial support, check out http://www.tektronix.com/learning/dig...

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