A digital multimeter is an electric device that measures resistance, current, and voltage in an electrical appliance. Digital multimeters have the following features which make them a better option over the analogue multimeters;
- Their display is digitalized. It may be LCD or LED.
- It has buttons that will serve various functions, including the on/off switch.
- It also has a rotary knob or a dial to select measurement value.
- And have several Sockets where the probes are connected.
Purpose of a digital multimeter
Digital multimeters are used to measure voltage current resistance and continuity of both alternating current and direct current. If you are an electrical work enthusiast, a digital multimeter is a tool that you should not lack. When you meet the device for the first time, it may seem not easy because of the symbols and figures on its face. For starters, below is a list of the symbols and what they stand for.
- V-: when the multimeters knob is in this setting, it will be measuring quantities of direct current voltage, e.g., a battery. In other multimeters, it may be denoted as DCV that stands for direct current voltage.
- V~: the setting will measure voltages, resistance, current, and continuity of the alternating current. Some other multimeter will denote it as ACV, i.e., alternating current voltage.
- ~: the setting will measure the continuity of a circuit. Whether it is complete or broken. Other multimeters will have a diode symbol rather than a wave sign.
- Ω; the setting will measure the resistance in a circuit and electric components
- DCA; stands for direct current amperage and will let the multimeter give measurement in amperes instead of volts.
- hFE; the setting will test for transmittance and direct current gain. It is not frequently used as the continuity test will serve the same purpose.
- It would be best if you did not get overwhelmed by the symbols. Only a few of them will be frequently used. The other symbols to note are the labelling of the ports. A digital multimeter has three ports with labels as follow
- COM; it denotes common, and it’s the port where the ground or negative cable black in colour should be fixed.
- VΩMa; when measuring continuity, voltage, resistance, and current of 200mA and less, this is the port where you should connect your positive probe. Other multimeters label it as mAVΩ. It merely stands for current in milliamperes and voltage resistance.
- 10ADC: it is the port where you should fix your red probe if you are not sure of the current you are dealing with. It measures current higher than 200mA. Some multimeters will label it as 10A.
It is necessary to note that if you measure current higher than 200mA and the red probe is at the port labelled VΩMa, and your multimeter will blow. Some multimeter will have a specific port for current tests, and others will share a port to measure current and volts.
Now with the understanding of the symbol, you can simply conduct a test of your choice. The ACV is among the symbols, and it is what the article will focus on. Its application and the steps to follow when conducting resistance, continuity, voltage, and current in an alternating current circuit.
Dealing with alternating current
When you are conducting any test on alternating current, the setting of your multimeter should be at ACV. This is because the AC has no polarity. You will achieve the correct reading. In any case, if you use the DCV your multimeter will blow. Below is how to test for current, continuity, resistance, and voltage in an alternating current circuit.
The first step is to set your digital multimeter to measure ACV or V~ by turning the knob or the dial to measure alternating current. Some of the digital multimeters operate on an auto range mode, where they will select the range automatically. But you should note that they cannot choose alternating current or direct current. You will have to do it manually. They are capable of choosing a range according to the possible volts or current in the circuit. Preferably set it at best possible range to avoid overloading the meter or getting infinite values. Below are the steps that will follow
Testing with a Digital Multimeter
- Connect the black (negative) lead to the common socket (COM). Note that alternating current does not have polarity.
- Insert the positive lead in the voltage socket labelled (VΩ). After you are finished, you can turn on the multimeter and check if it is working by connecting the black and the red probes. The reading on the screen should be 0.5 and less for a proper functioning multimeter.
- Connect the probes to the circuit you want to test simultaneously. To get the correct reading, you should avoid any human contact or other external contacts with the tip of the probe.
- Note the reading on the screen, which is in volts. The reading indicates the number of volts between the two points.
- Withdraw the probes starting with the red one and then the black one.
The data you will get will be in volts. In this setting, you can test for resistance, continuity, and voltage in a circuit. For current, the reading should be amperes, and you have to change settings.
With the data now, a digital multimeter will help you analyze your test. It has a range button that, when pressed during the analysis, will select a fixed and specific range. The hold button will capture and record a stable reading. When recorded, you can access the readings after the test. A max/min button that will help achieve the highest and the lowest readings. You can also set a reference value for your multimeter by pressing the REL button.
Note when conducting a test on an alternating current circuit, you should avoid mistakes such as jacking the positive lead on the amperes port rather than the voltage port and interchanging the probes.
The features I have discussed above may be very different in a particular digital multimeter model. It is advisable to check on the manual provided by your model manufacturers because what I have given is just basics. After you have understood the concept, you will have a good time experimenting and conducting a test on your electric appliances by yourself.