Multimeter buying guide

The multimeter is one of the most useful tools to anyone working with electronic or electrical devices or circuits. The basic multimeter is capable of measuring voltages, currents and resistances. A continuity test buzzer is also found on all current models. Many models, even cheap ones, are also capable of measuring temperatures, capacitances and frequencies. You can use a multimeter for something as simple as detecting a broken wire, measuring battery voltage or something more challenging such as finding a faulty transistor on a complex circuit. In this post I will share some essential information about multimeters and some advice for multimeter buyers. 

How multimeters work?

The working principle of a multimeters is really simple. Multimeters work by comparing external readings taken with two probe wires against an internal reference voltage. The result of the comparison is then shown on an LCD display in case of a digital multimeter or a panel meter in case of an analog multimeter. The accuracy of the multimeter measurements is directly related to the accuracy of the reference voltage. Most portable multimeters are powered from one 6F22/6LR61 9V battery or two AA 1.5V batteries.

Portable multimeters and bench multimeters
Multimeters can be of the portable or bench (fixed) type. A typical bench multimeter will have one or more bigger displays, bigger knobs and switches and more inputs. They are mains (AC) powered. In this post I will address portable multimeters.

Digital vs. Analog multimeter

Until the late 80's early 90's most multimeters where analog. The analog multimeter is easily identified by the meter panel with its big needle. Analog multimeters are fine, but they are less precise than digital ones and take more time to display the measurements. Nowadays digital multimeters are so cheap that anyone can afford one or more! 

Multimeter features

A basic multimeter will measure AC and DC voltages, DC currents and resistances. Most will also have a continuity test (buzzer) and a diode test mode. Many models will also feature temperature, capacitance and frequency readings. Some will have true RMS readings. Another useful feature is automatic data hold. One feature that is commonplace in cheap multimeters but not in more expensive ones is the transistor tester function. This is the case because it's a rarely used feature and cheap multimeter manufacturers try to offer as many features as possible to captivate potential buyers.

Multimeters are capable of taking measurements across a wide range of values. For measuring and display purposes this wide measuring range must be split into several narrower ranges. A multimeter with more ranges is more desirable than one with fewer ranges, because it will allow for better accuracy. Many digital multimeters have the autorange feature, which means that range selection is done automatically by the multimeter. Display resolution is limited by the number of digits of the display and the multimeter chip. A 3 1/2 digit display multimeter will display values between -199 and 199. A multimeter with a 4 1/2 or more digits display will allow for more resolution. If speed of measurements is important, higher quality multimeters usually are faster at taking readings.

Multimeter safety

Since most multimeters are capable of measuring high voltages and currents, they must protect the user from any accidental over-voltage discharge or over-current. The most basic protection is given by one ore more fuses on the multimeter inputs. Good quality multimeters will have other additional protection components like VDR's. For protection purposes multimeters are classed according to the level of protection built-in as CAT II, CAT III or CAT IV and a certain maximum voltage level. But, even if a multimeter is claimed as having CAT III or CAT II level protection, this might not be a guaranty of safety, specially with very cheap multimeters from unknown brands. I don't recommend connecting a cheap multimeter to the mains power without first opening the multimeter and checking visually the quality of the protection circuit, soldering and wiring. If you are going to use the multimeter for low voltage low current applications then, safety wise, any cheap multimeter will do the job.

Inside a 20 USD digital multimeter

Are cheap multimeters any good?

Yes and no. For starters it depends on your definition of 'cheap' and 'good' and what you expect from a multimeter. You can buy a very acceptable basic multimeter for low voltage applications for just under 10 USD! Build quality aside, generally a multimeter will be more expensive if it has higher precision and accuracy. It will also be more expensive if it offers better protection (safety!). You are not going to find a general purpose good quality multimeter for 10 USD, 20 USD or probably even 30 USD. However, if you are not going to measure high voltages or currents (like mains power), the level of protection found on a cheap multimeter is usually good enough. So, if you are not going to measure mains voltages but just low voltages, fear not buying a cheap multimeter.

Three cheap multimeters: 5 USD (left) and 20 USD (center and right).

A better multimeter: the Uni-T 61E.

How many multimeters should I have?

It is advisable to have at least two multimeters. There are several reasons but, for starters with two multimeters you can make measurements with two different devices, greatly reducing the possibility of inaccurate readings. If you only have one multimeter, a faulty multimeter might go unnoticed and trick you. If you have two or more multimeters you can immediately check one against the other and realize that one of them is faulty. It's also often necessary to check voltages in more than one point in a circuit at the same time. Or, you might need to measure voltage and current at the same time.

Final advice

There are many models of digital multimeters, with different features, various degrees of quality and prices. Usually you get what you pay for. Don't expect miracles, quality costs money. Check what's available. Make a list of the features you need or value more and those that are desirable. Choose a multimeter rated for the highest category you could be working in. Then, look for a voltage rating for that category matching your needs. Use Google to get the multimeter's full specs and, if possible, the user manual. Google for user reviews. Good luck!

Need to buy a multimeter?

I buy most of my electronics, tools and measuring equipment from Dealextreme and Banggood in China. They have low prices, friendly and helpful staff and will offer a solution if something goes wrong with your order. They have warehouses in Europe and the USA and can provide faster delivery for many of the items. I get a small fee if you buy from them through links in MakerCorner. So, please support my work by clicking on the following links. Thank you!

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