In this lesson, you will:
- Learn what a multimeter can do for you
- Learn to use a multimeter
- Learn to use it safely
A multimeter is your best friend when playing with circuits. A typical multimeter can measure:
- Voltages in DC and AC
Advanced multimeters can do more than that. Some can measure temperature, capacitance, frequency of signals, etc.
Analog multimeters and digital multimeters
In multimeters, there are two kind of multimeters; digital and analog.
Digital multimeter is the most popular multimeter. The result is easy to understand, and some digital multimeters have automatic range detection. A digital multimeter measures values with digital circuits, by sampling multiple values in a very short time.
Analog multimeter is a multimeter with an analog meter. It is less popular these days, but sometimes it is still useful. Instead of displaying the result on digital screen, it has a analog meter and an indicator to point to a number. An analog multimeter measures values with analog circuits. The result is more accurate reflection of the reality. For example, digital multimeters cannot reliably measure a short pulse of voltage.
In this lesson, we will discuss about a digital multimeter.
Parts of a multimeter
A multimeter has a display that shows measurement. The display is usually an LCD display, sometimes, with a backlight LED so that you can see the result in a dark place.
A typical multimeter has a dial to change its functions. Functions available depends on products. With the dial, you choose what you want to measure and how much you expect, the range. When you measure a voltage in a small circuit with a microcontroller, you choose the voltage function, and its range. Typical small circuits operates on lower volts, such as 3.3 V, or 5 V. The range you should choose is more than the voltage. Some multimeters has auto-range detection feature, thus, they do not have ranges. Additionally, a dial in a position may point to multiple functions. In that case, you need to choose the function you want to use by pressing a “function” button. The display shows which function is selected.
A typical multimeter has three ports: a red positive port, a black common port, and another red port for large current, commonly labeled with “10A”. You usually use the former two ports. When you use the “10A” port, you must be very careful because large current will flows in to the multimeter and the circuit..
Probes are two cables, in red and black, with metal tips. When you measure voltage, the red one is connected to a point at higher voltage, and the black one is connected to a point at lower voltage. You may reverse the probes, and the multimeter displays negative results.
Selecting functions and ranges
The golden rules:
- Change the function of the multimeter only when it is not connected to anything
- Ensure to start from higher ranges
- Double-check the function and the range
Before using a multimeter, test the probes. Probes can degrade and they are are consumables. Degraded probes lead you to wrong conclusions, and might kill you.
- Select the Ohm meters on the selector dial (choose milli-ohm range)
- Plug the black probe into the common port
- Plug the red probe into the port labeled with “Ohm”
- Touch one tip of the probes to another
- The result on the display should be less then 1 ohm (the lower, the better)
If not, the probes are degraded. Replace probes with a pair of known good ones.
Other lessons in Electronics Basic Course: