We are going to learn how to use a digital multimeter: manual and auto ranging types. After gaining 15 years of experience with several digital multimeters I can guide you with exact information you need to know about a digital multimeter and what things can go wrong as a beginner while using one.
So, you brought a brand new multimeter or planning to buy your first digital multimeter and you want to know how to use one and how difficult or easy it would be; if so you landed on the right place.
We will see:
- How to use a multimeter to measure AC / DC voltage.
- How to use a multimeter to measure current.
- How to use a multimeter to measure resistance.
- How to use a multimeter to test continuity.
- How to use a multimeter to test a diode.
- How to use a multimeter to measure other electrical parameters like frequency, capacitance, transistor gain and temperature.
- What are hold, backlight and auto power off function in a multimeter?
- For how long can you trust your multimeter?
How to use a multimeter?
Fundamental steps for any multimeter usage:
- Insert the probe’s banana plug into appropriate sockets of the multimeter.
- Turn the range selector switch from off position to the desire function and range gently.
- Hold the probes with two hands well above the two metal prongs.
- Touch the sharp metal tips of the probes to the desired points of a circuit or a source.
- Wait for a moment to get a stable reading on the multimeter and take note of the measured parameter.
That’s how easy to use a multimeter.
How to measure voltage using a manual range multimeter?
Let’s measure voltage of a 9V battery.
- Banana connector position: COM and “mAV ohm”.
- Turn the range selector to the DC measurement and since we are going to measure 9V, we cannot use 200mV or 2V range; so the next highest range is 20V. With 20V range you can measure voltage up to 19.9V.
- Now touch the battery terminals with two probes, battery voltage will appear on the display.
Please note that we did not use 200V or 600V range, higher the range we select lower the accuracy we get. This is true for any parameters in a manual range multimeter.
If we swap the probes we will get (–) with the reading which we need not to worry about and the voltage readings will be still the same.
How to measure voltage on an auto range multimeter?
The advantage of having an auto ranging multimeter is that we no need to select a range; instead we just need to select the function which we are about to measure.
- To measure DC voltage on an auto range multimeter select “V”. Take a note on the banana connector position. The display will show “DC” and unit “V” and mode “Auto”.
- Now place the probes on the battery terminal, voltage will be displayed.
AC measurement on manual range multimeter:
We don’t recommend measuring any high voltage AC circuits as a beginner, but for illustration purpose we are showing you how to measure AC mains.
- The place where I live, the supplied voltage is 240V AC. To measure 240V, 200V range cannot be used so we have to select any other range greater than 240V using the selector switch. Here the next highest is 600V.
- Now insert the probes of the multimeter to live (or hot) and neutral. The polarity of the probes doesn’t matter here.
Caution: You should hold the probes firmly while measuring AC mains voltage. I couldn’t do because I had to hold the camera.
AC measurement on Auto range multimeter:
- Select “V” and by pressing the yellow button once, multimeter switches from DC to AC. By inserting the probes to live and neutral, you can measure AC mains voltage. The banana connector position is same as DC.
- The way of switching from DC to AC measurement may change from multimeter to multimeter (brand).
How to measure current using multimeter?
Current measurement in any circuit with any measuring device is done by connecting the measuring device in series with the circuit, as illustrated below:
Current in a circuit can be measured only when a load is operating, only then you can determine how much current the load is consuming right now.
Very important note: You should not connect a multimeter in ammeter mode in parallel with any power source, if you do so you are effectively short circuiting the power source.
Most multimeters have a separate socket (to insert red color banana plug) to measure high current. If you look at the current measurement socket, it will be mentioned 10A, 15A etc. which means you can measure 10A max or 15 max etc. some times with a time limit like 10 sec max, 15 sec max etc. So you can only measure up to the current limit mentioned, till the specified time, beyond which you will damage the multimeter.
You can also measure current using “mAV ohm” and “COM” sockets but only up to 200mA for this particular multimeter, if you try to measure beyond the specified limit, fuse will blow. Once the fuse blows, other functions like voltage, resistance etc. may not work till you replace the fuse.
Current measurement using manual range multimeter:
- If you don’t have a rough idea how much current is flowing, select the maximum current range i.e. “10A” using range selector switch and insert the banana plug to 10A socket.
- Connect the multimeter in series with the load; here we are using a 6V incandescent bulb.
- The multimeter reads 0.25A or 250mA, which is well beyond the range of socket “mAV ohm” can handle. If we directly used “mAV ohm” socket, fuse would have blown.
This is how we measure current for AC and DC. This particular multimeter did not feature an AC current measurement function.
Current measurement using Auto range multimeter:
Again the steps are same as mentioned above. Since I already know that this bulb consumes around 250mA and this particular auto range multimeter can accept up to 600mA with “VmA ohm” port, I am going to measure current without inserting the red probe to 10A socket.
- Turn the selector switch to “mA” position, to measure current in mA (up to 600 mA limit).
- Or Turn the selector switch to “A” only if you are inserting the red probe to 10A socket to measure current above 600 mA and the measured value will be in ampere.
Banana connector position:
- Connect the auto range multimeter in series with the load.
The multimeter measures 265.2 mA. This procedure is same for AC current measurement as well but you need to switch from DC to AC measurement by pressing the yellow button.
How to measure resistance using manual range multimeter:
Let’s try to measure the value of a resistor using manual range multimeter, we are going to measure 10K resistor as sample.
- Plug the banana connectors to “COM” and “VmA ohm” sockets.
- Select 20K range using range selector switch.
- Touch the metal tips of the probes at two terminals of the resistor.
- Wait for a moment so that readings get stabilized and take a note of the reading.
The multimeter reads 9.79K ohm for a 10K resistor.
How to measure unknown resistance using manual range multimeter:
In the above case we had a known resistance value of 10K, but what to do if the resistor color rings are not visible or you don’t know how to read resistor value by decoding color code to select appropriate range on multimeter.
You can measure an unknown resistance value by:
- Turn the range selector switch to the maximum resistance, in this multimeter it is 2M or 2 mega-ohm.
- Measure the resistance. Lower the range to 200K if you think 2M is not a suitable range and the reading displayed is single digit.
- Now try measuring using 200K range, if the reading shows (say) 10K or 15K, you can select a lower range 20K because it is the nearest range to the measured value.
- By selecting 20K you will get the precise resistance value.
- Say if you read 25K ohm with 200K range, it is a common sense that you cannot select 20K range for 25K ohm resistance. Even if you try to measure, multimeter will show “1” or “OL” meaning the readings are out of range and you need to select a higher range.
In conclusion if you have an unknown resistance first select the maximum range and lower the range gradually and stop when you find the suitable range for the unknown resistance.
How to measure resistance in auto range multimeter:
It is very easy to determine resistance using an auto range multimeter.
- Select ohm symbol using selector switch.
- In this auto range multimeter several functions are clustered together at a point.
- To select resistance, I had to press the yellow selector button few time to bring the multimeter to resistance measurement mode out of other functions.
- The way for selecting resistance mode may vary from multimeter to multimeter.
- Now by touching the metal tips of the probes at to two terminals of a resistor, the value will be directly shown with a suffix “K” for kilo or “M” mega or no suffix if the resistance is below 999 ohm.
- The auto range multimeter reads 9.88K ohm.
How to use a multimeter for continuity testing:
Continuity test is an important function in a multimeter, using which we can debug many several issues in a circuit. A multimeter in continuity mode, when two probes touches each other or made contact with a wire / PCB trace that completes current path between two probes, the meter will show zero resistance and beeps loudly, indicating there is low resistance path between two probes.
If there is some resistance between two points the meter won’t beep but shows resistance reading. A manual range multimeter can show up to 2K ohm resistance in continuity test mode.
As an example I am going to trace PCB tack using a multimeter:
- You need to turn the range selector switch and point towards the buzzer symbol. It will show “1” meaning the resistance between two probes are out of measuring range (above 2K ohm).
- When the two probes come in to contact electrically the meter reads 1 ohm and beeps, indicating that the PCB trace is in good condition.
Continuity test using auto range multimeter:
It is same as manual range multimeter; it beeps and shows the resistance.
- You need to point the selector where the buzzer symbol is located and it is with the cluster of other functions, press the yellow selector button to select the continuity function.
- When continuity is made the resistance between two probes are 0.3 ohm and beep, indicating the PCB trace is in good condition.
How to use multimeter to test diode:
Diode test mode can be used for testing semiconductors like diode obviously, LED and transistor. When diode mode is selected the probe outputs DC voltage around 2V.
When you touch the probes with a diode in forward bias, it will show the voltage drop across the diode, meaning how much voltage lost due to voltage passing through diode.
- A healthy silicon diode shows voltage drop of 0.5V to 0.8V.
- A healthy germanium diode shows voltage drop of 0.2V to 0.3V.
- If the diode is reverse biased it should show “1” or “OL.
- A bad diode (shorted) will not show any voltage drop in both directions (0V).
- Bad diodes also show “1” or “OL” (open circuit) in both directions.
- A diode can be considered bad if there is any abnormal voltage drops other than specified values in the data sheet.
Diode test using manual range multimeter:
- Turn the selector switch towards diode symbol and touch the tips of the probe on both terminals of diode as illustrated.
- If the meter shows “1” which means the diode is reverse biased, reverse the probe it will show some readings in “mV”
- The below shown multimeter reads 922 which is 0.922V or 922 millivolt.
Note: The above shown reading is incorrect this is due to low battery as indicated in the multimeter display. It is very important that you should replace the battery as soon as the meter shows low battery symbol because it will interfere with the accuracy of the reading.
Diode test using auto range multimeter:
- Turn the selector switch towards the diode symbol and touch the probes at both terminals of the diode. If the diode is reverse biased it will show “OL”
- If the diode is forward biased it will read some voltage drop. Here we are getting 0.5V drop which indicates that this silicon diode is healthy.
Till here we saw how to measure voltage, current, resistance, continuity and diode testing. These functions are always available on all digital multimeters. Now, we are going to see some additional functions of multimeter that may or may not exist in your multimeter.
Transistor tester on multimeter:
On some low-end multimeter you can find a socket where you can insert a transistor (NPN and PNP) and the meter will show you the gain of the transistor.
Before you insert the transistor, you need to know what type of transistor it is and its pin diagram. You can find details of transistor in its data sheet.
- To know the gain of a transistor, turn the selector switch to “hFE”. We no need multimeter leads (probe) in this mode.
- Insert the transistor in its correct socket type i.e. NPN or PNP.
- Wait for a second or so to get stabilized reading.
- Here the multimeter shows 855 as gain of this BC 547 NPN transistor, which is very close to its data sheet specification (800). So this transistor functions correctly.
The problem with this method of testing transistors is that not all transistors fits in this socket and in many cases you need to test a transistor on a PCB which is soldered on to. Another issue is it is very difficult to memorize the gain of 1000s of transistors that at-least fits in this socket and a loose or damaged socket or a rusted transistor terminal will give you incorrect readings.
Professionals don’t use this function, instead they use diode test mode and multimeter leads to test a transistor properly. In this method, gain of the transistor will not be known, but we can determine whether the transistor is in good condition or not.
Explaining this method of testing transistor here will be out of scope of this article, you can Google it.
Thermometer on multimeter:
Temperature measurement feature is available on some mid-range multimeters. You will get a temperature probe which is basically a thermocouple (a wire junction of two dissimilar metals) which produces a tiny voltage on heating on one end; this voltage is converted to temperature readings. You can measure temperatures well above +200 degrees Celsius or below 0 degree Celsius and you can even switch between *F and *C.
To measure temperature:
- Insert the temperature probe as shown above.
- Turn the selector switch towards *C/*F position.
- You can see the room temperature instantly.
- By touching the surface of heat sink or any solid material with the end of the probe, you can measure the temperature of the material.
- Don’t use this probe for measuring temperature of any liquid; this type of probe is suited only for dry measurement.
Frequency measurement on multimeter:
On some mid-range multimeters we can find a function which can measure frequency and duty cycle. But this is not substitute for an oscilloscope and you should not use this for measuring high frequencies for some serious measurements. You can definitely use this for hobby and learning purposes.
You should not use a multimeter to measure frequencies above 100 KHz because accuracy of the reading may get compromised and yes, accuracy may vary multimeter to multimeter a little bit.
Here I am going to measure frequency of square wave from astable IC 555 oscillator.
To measure frequency on a multimeter:
- Turn the selector switch towards “Hz / %”.
- Connect the black probe to ground supply and red probe to the output pin.
- Wait for a second to get stabilized reading. Here the multimeter shows 142.1 Hz.
- By pressing the yellow button on this particular multimeter we can measure duty cycle.
Caution: Do NOT measure frequency of 230V / 120V AC supply directly unless the multimeter is specified to do so. You should step down to 12V or below using a transformer and take measurement.
How to measure capacitance on a multimeter:
Again, on some mid-range multimeters we can find capacitance measurement feature. From our testing the multimeter was doing a good job of figuring out the actual capacitance of a capacitor. You can measure capacitors values ranging from pico-farad to nano farad to micro-farad or above.
Capacitance can be measured by:
- Discharge the capacitor completely by short circuiting the terminals for low voltage capacitors. For high voltage capacitors use a resistor with value around 100 ohm rated for at-least 2 watt for 5 seconds and then short circuit. If you short circuit a high voltage capacitor when it’s fully charged you may get violent sparks.
- A capacitor must be removed from the PCB before measurement, only then you will get accurate measurement.
- Now, turn the selector switch towards the capacitor symbol.
- The red probe is +Ve and black probe is –Ve.
- For electrolytic capacitors the red probe should touch +Ve terminal and black probe should touch negative terminal. For un-polarized capacitors, meaning no specified +Ve and –Ve terminals the probes can touch in any polarity.
Touch the terminals of the capacitor steadily with probes until the reading get stabilized. Multimeter will charge the capacitor while measuring so, it will take few seconds.
The multimeter reads 10.52 uF for a 10uF / 16V rated electrolytic capacitor.
We have concluded all the important features of a manual and auto range multimeter. Now we are going to see some common features that are available on almost all multimeters and can be handy while using a multimeter.
This feature is handy while working in less lit environment. When you press backlight button once it will light-up the display for 5 seconds usually, some multimeter keep the backlight ON for 10 sec or more. The backlight goes off after pre-programed time in the multimeter, you can press again of you want.
In most of the multimeters we can see a hold button and to be honest it is a useless function. When you press hold button the readings on the multimeter will freeze. You may ask what’s wrong with this function. Well let me explain.
Most inexpensive multimeters are trying to emulate a feature that only high end multimeters have, that costs hundreds or even thousands of dollars.
Hold function is used when your hands and eyes are busy on the circuit and you need a person to read out the readings. The hold function’s job is to eliminate the need for a second person’s help by automatically locking the readings after few seconds when readings get stabilized.
But with inexpensive multimeters when your hands and eyes are busy on the circuit, you need a third hand that doesn’t exist to press the hold button.
Auto Power Off:
Auto power is an important feature for a multimeter; we can assure that no matter how perfect you are; you will forget to turn off your multimeter at some point. If your multimeter doesn’t sport auto power off feature you battery will go drain soon.
Multimeters that sport auto power off feature would have mentioned on the multimeter. Very cheap multimeters don’t sport this feature.
Fuse and battery replacement:
You need to replace the battery as soon as your multimeter shown a battery symbol on the display. Using your multimeter with low battery will give you unreliable readings.
To replace battery you need to unscrew the battery compartment as shown below and replace with same type of battery:
To replace battery on some multimeters you need to unscrew the whole back cover as shown below and replace the battery of same type:
In case multimeter fuse pops, you have to replace with exact same fuse type and ratings. Most of the time fuse pops when you try to measure current beyond the capability of the selected range. Most beginners pop the low current fuse often.
Once the fuse popped none of the functions will work until you replace it. Don’t DIY hack or use thin conductive wire to bridge the fuse connection. If something goes wrong again your multimeter will malfunction instantly or a violent small to medium explosion could occur if you are measuring high voltage / current.
For how long a digital multimeter can maintain its accuracy?
Like any other electronic measuring instruments, multimeter will lose its accuracy overtime. Several instruments are re-calibrated during its life time, but multimeter is not user calibratable in general.
So how long a multimeter can be trusted?
We are giving this answer based on our experience; some dirt cheap multimeter can only last 6 months to a year. An inexpensive yet decent multimeter like shown in this article can last up to 3 years if handled softly. The auto range multimeter came with a calibration certificate and they claimed its accuracy can lasts up to 2 years. Branded and hi-end multimeters can last 4 years or more if handled according to manufactures recommendations.
You can also find how long your multimeter’s accuracy lasts in its user manual or in its calibration certificate that came along with multimeter. If you soft handle the meter, it may outlast the manufacturer claim.
If you have any questions regarding multimeters, you can ask us in the comment. You can anticipate a guaranteed reply from us.