How to calibrate a digital multimeter
You have decided to buy a new digital multimeter. You wanted it for a very long time. And here it is, in front of you, in a box. You open the box and you are eager to test it, and so you begin testing your brand new multimeter. Although the multimeter shows data, it seems very wrong.
What is going on?
There is no reason for panic, your new multimeter probably only needs to be calibrated. Luckily, you came to the right place. Most new multimeters are not calibrated very precise. Especially if they are made in China and if they are somewhat cheap, you can be sure that they are not calibrated at all because they have only one potentiometer in them. If you have a more expensive multimeter worth one hundred dollars or more, then your multimeter is probably calibrated. More expensive digital multimeters come with three or more potentiometers.
Inbuilt potentiometers are used to calibrate the multimeter by extracting an average value. When you have three or more values, the average value is highly likely to be precise.
If you have a more expensive multimeter, great, if not, borrow it from a friend of yours, because although you probably have a cheap multimeter, it is possible to calibrate it to be as precise as an expensive one.
So, how do you calibrate your brand new digital multimeter?
You will need a calibrated or more expensive multimeter, new multimeter that you wish to calibrate, modular power supply and a screwdriver.
First, plug the probes in the multimeters. Turn the multimeters on and set them both to the same setting, depending on the type of power supply that you are using.
What you’ll want to do next is to unscrew the back of the uncalibrated multimeter. Take a look at the circuit board in the back of the multimeter and locate the potentiometer. Most potentiometers look like elongated screws with a huge gap in the middle. Most of them are also on a small pedestal.
Connect the probes (it is best to have clamps instead of probes, but you can do it with probes too) to the power supply and turn the power supply on. When I write „power supply“ I don’t mean the city electric grid. I mean the power output that you can buy, the type of power supply that runs on batteries. If you can’t or don’t know where to buy the power supply that runs on batteries, grab an old remote and carefuly extract the battery holder with wiring.
That is the safest type of power supply for this type of work.
So, after you have connected the probes or clamps, whatever you prefer, to the power supply, turn the power supply on – plug the batteries in and make sure that you have connected the clamps or probes to the correct wires (check the poles). Confirm that you have set the multimeter to the correct setting (for most power supplies – volts) and check the results of the measurement on the screens of the multimeters. You will probably notice that a somewhat large, oscilating difference in results exists.
Be absolutely sure that the multimeter that you are using as a reference is calibrated.
What you’ll want to do next is to take a screwdriver and turn the potentiometer slightly while looking at the results of both multimeters. You will find out that the results are changing according to the direction in which you are turning the potentiometer. Turn the potentiometer gently and precisely to the required direction in order to calibrate the multimeter as precise as possible. You will discover that it is impossible to calibrate your new digital multimeter one hundred percent. However, it is possible to calibrate the multimeter to ninety eight or ninety nine percent accuracy.
You shouldn’t attempt to calibrate more expensive multimeters such as Fluke 87V (see on Amazon.com) because most of them are already calibrated and because there is a very high risk of damaging or completely breaking the multimeter during the attempted calibration. I will explain why in the following paragraph.
I can’t emphasize the following enough:
Although you have been successful in calibrating this multimeter with one potentiometer, don’t try to calibrate multimeters with more potentiometers, not even the cheap ones. If you attempt to do so, the best outcome is damage to the multimeter, the worst outcome can be an explosion. As we need to have the back part of the multimeter open as we calibrate them, if the multimeter explodes, it could blow right in the operator’s face.
You now know how to calibrate your new multimeter.
I highly recommend that you adhere to all safety protocols while doing this and if I were you, I’d get those plastic safety glasses and have them all the time while calibrating. Just in case. Although your new multimeter is still not like the more expensive one in terms of safety, it can now measure as accurate and as precise as an expensive multimeter.