Want to know what the multimeter symbols actually mean?
Great stuff, you are in the right place.
In this ToolsGaloreHQ.com guide, I will show you:
- All the different symbols
- What they represent and measure
- Some key hacks when using these symbols
- And so much more!
Before I get into the details on what each symbol represents and does, please review the table of contents below.
What The Multimeter Symbols Mean
Without wasting any of your time, let’s get into each of the symbols in more detail.
1. True RMS
The True RMS tag on a multimeter basically informs the user that the multimeter is capable of providing Root Mean Square Values irrespective of the shape of the AC waveform.
To fully understand why this is significant, we need to get a grasp of how most multimeters measure and show AC signals.
For a purely sinusoidal waveform all multimeters capture the Root Mean Square (RMS) value. This is what is depicted on your LCD display.
The RMS value of any sinusoidal signal is determined by taking the square root of an instantaneous value, averaged over a period of time.
All multimeters do this – the challenge comes when the alternating signal is a square wave, triangular wave or an AC signal that has a very large harmonic component.
These types of signals are typically found within HVAC applications and variable speed drives to name but a few.
To give you an example, a normal RMS multimeter will provide a 10% measurement uncertainty. Meaning that if the actual measurement is 230 Vac. Your multimeter will show a value of anything from 207 Vac to 253 Vac.
A True RMS multimeter on the other hand has a 0.5% measurement uncertainty at low frequencies (50 or 60 Hz) and up to 2% for frequencies in the 1 to 5 kHz range.
Therefore the real value of the TRUE RMS measurement capability comes when you are measuring non-sinusoidal AC voltages or currents.
2. Range Button
The Range Button is typically found within auto-ranging multimeters. This button is very useful because it allows the user to practically select the measurement range of an anticipated value.
Hence basically operating the multimeter in manual mode.
The reason anyone would want to do this is because, whenever you use the multimeter on autoranging, there is a period and portion of time whereby the multimeter will need to perform internal calculations to determine the range automatically.
This takes up bandwidth and by simply using the multimeter in manual ranging mode, you completely reduce the need to this additional computation period
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3. AC Voltage
This is the signal for measuring Alternating voltage. Most multimeters have a range and an accuracy for their AC measurements so please consult the datasheet to get concise information.
4. Auto Backlight Switch
This button serves to turn the backlight on or off. It is very helpful in circumstances when you are using the multimeter in poorly lit areas.
Such as the bonnet of a car or within the panel of an HVAC system.
5. DC Voltage
This is the standard DC measurement voltage port. Setting the knob at this location will provide you with a DC
6. millivolts (DC)
This is the selection for the millivolt measurements. If you know that the maximum voltage will be less than 1V. Then this is the correct setting to use as it will provide the most accurate measurements.
This is the knob selection for measuring resistance. Most multimeters have a resistance range that can be recorded. Consult the datasheet of your specific meter to get the most out of it.
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8. Continuity Beeper
This is the selection for the continuity beeper. It will typical sound a high pitched and audible sound when there is continuity between the two terminals.
In the Fluke 117 multimeter as an example, continuity is determined when the resistance is less than 20 Ω, whilst the beeper will turn off at anything greater than 250 Ω.
For your specific multimeter be sure to consult the user manual for specific operating conditions of the continuity beeper.
This is the selection for when you want to test a diode. Important to note is a forward biased diode will typically have a voltage drop ranging between 0.2V and 0.8V based on the type and make up, when in operation.
When the diode is bad, the multimeter will show an “OL” on the LCD display, which basically means that the diode is operating like an open circuit.
10. Input Terminal
This is the first of the input terminals. It is for measuring the voltage, capacitance, frequency, diode and continuity. This is typically the terminal through which you would install your red lead.
11. Safety Rating
As you can see in the image above, this multimeter has a CAT III (600V) rating. What this practically means is that between the Input Terminal (11) and the Common Terminal (12), the multimeter can handle a steady state voltage of up to 600V.
According to the standards IEC 61010-1 a multimeter CAT III (600V) should be able to measure equipment for three phase distribution systems, single phase commercial systems and all lighting applications (including for industrial plants).
12. Common Terminal
The Common Terminal can be thought of as the ground, it is the common point through which all the internal components within the multimeter join completing the circuit.
13. Input Terminal
The Input Terminal for Number 13 is basically for measuring either the AC or DC current.
Most multimeters have a limit on the maximum current that can be measured. On the image of the Fluke 117 – this can be seen by the “10 A Fused”.
This means that under normal conditions you can measure currents up to 10A, beyond that the safety fuses will blow.
14. DC Current
This selection is practically for the reading of the DC current measurement. Depending on your individual multimeter you will have different ranges and accuracies. These are to be confirmed via the product manual or datasheet.
15. AC Current
This selection is for the measurement of AC current. The ranges, resolution and accuracies are to be confirmed via each individual multimeters datasheet.
16. OFF Button
This button selection serves the purpose of turning off the multimeter completely.
17. HOLD Button
The HOLD button practically ensures that a value is kept frozen on screen. This feature is very helpful when you need to capture a measurement. As opposed to needing to remember it via memory.
18. MIN/MAX Button
By enabling this button you will be able to capture the minimum and maximum measurement values over a specific period of time. This is very helpful in instances were you are trying to determine the magnitude of transients, such as motor start up current.
Additional Multimeter Symbols
This function is not a feature of the above Fluke 117 multimeter and hence why is was not shown. However when you go more to the higher end of the spectrum you will often come across various multimeters with a REL button. See the image below – I am pretty sure you have come across it before.
What this Button does is allow for the capability to perform RELATIVE measurement.
For example let’s say you are in the process of measuring the voltage difference in your home between the distribution box supply and the main’s wall socket.
There are two ways you can go about this, you can carry around a pen/paper or even a digital device like a phone and record each and every measurement in relation to the distribution board supply.
Then after measuring perform some basic mathematics to see the voltage drop between each socket in relation to the mains supply.
Another (and arguably more simpler method), is to set the REL button whilst you are measuring the mains supply.
What will happen is as you are measuring the mains supply you will get a voltage typically within the range of 120 Vac. By pressing the REL button. This value get’s stored and your multimeter resets to zero.
Now by going to a wall socket and measuring 117 Vac for example, you multimeter will actually show -3V.
The reason being that the measurement is now being viewed in relation or relatively to the original 230V.
The beauty of this function or symbol is that you can then go and test all other voltages in relation to the 230V.
Most people have seen this REL button but very few ever fully exploit it’s full potential.
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Final Thoughts On Multimeter Symbols
As you can see from the images and the explanations above that the various multimeter functions all serve a distinct purpose.
I used the Fluke 117 simply because it provides over 90% of the various multimeter symbols anyone could come across. I also provided an explanation on the often under utilized REL button.
I had a lot of fun creating this article and I hope that you have learnt something that you might have not known otherwise. Please feel free to share this article on social media and let’s get more people familiar with what all the different multimeter functions actual mean.