How to Choose the Right MultimeterMay 12, 2020 by David Peterson
Most every engineer knows that there is no replacement for having the correct tool. This is especially important in testing and repair when every subtle characteristic of the tool may influence the readings.
Having a good multimeter is great, but it’s equally important to possess the correct accessories and attachments, or else the meter is useless.
Choosing the Right Test Leads
Nobody would ever buy a really expensive car and forget to include wheels. You’d never buy a nice new house and choose to ignore that it doesn’t have doorknobs. Likewise, it’s a terrible idea to invest in a quality multimeter and forget to consider the test leads - after all, it’s the only way the meter will connect to the outside world.
A whole assortment of various test leads and attachments.
When it comes to test leads, there is a surprising variety. Most meters will include the standard default set with a single set of red and black cable, each with a thin silver tip. It works sufficiently for most tasks, hence being the default choice, but it won’t work in all situations. As always, I cannot provide an overview of every test lead in existence, since I’m certainly not familiar with all cases and situations, but this article will share many of the common choices.
The Standard Set
Basic multimeter leads must always include a set of 2x cables, and most of the time one is red the other is black. They usually have about ¾ inch of exposed metal at the end, terminating with a pointed tip. About 1/4 inch away from the end is a small shoulder, used for anchoring the test lead inside some devices such as industrial terminal blocks, or attaching some extra cable which grabs the metal, giving it a point to connect without sliding off the end.
A few variations of this basic cable style exist, and one that I have found useful includes a very short threaded shoulder just as the metal tip begins. Many end attachments such as alligator clips and grabbers may use this thread to provide a great secure attachment. Although not always vital, it does provide some security in making measurements.
A close-up of several ‘standard’ meter leads. They include the default standard, the one with a small threaded section, and the insulated fine-point tips from left to right.
Another common option is close to the normal lead, but only a very fine point is exposed at the very end. When making measurements of very small points that are located close to each other, touching the two leads can cause a short circuit and instant irreparable failure. The tightly insulated leads help keep the circuit safer for those tiny measurements.
They resemble the mouth of an alligator. These clips are designed to securely connect to test points on circuit boards or exposed wire ends. With one lead securely clamped, it leaves one hand free to ensure that safety can be taken and the instruments and controls may be adjusted as necessary.
Most of the time, they will consist of small end attachments that simply slide or thread onto the end of a normal test lead.
Other times, it may be an external cable that clamps to both the test lead and to the circuit board, although I’m not a fan of this option. Too many times the cable has come off the end of the test lead. Harmless in all of my cases, but if the situation was expensive or potentially hazardous, I’m not going to take the risk.
A few alligator clip ends. Note that the exposed metal one usually has an insulated jacket over the top, but it’s been removed to show what it looks like inside.
A final option is sometimes the alligator clips are permanently located at the end of the test lead cables. In other words, it’s devoted to being alligator clips only. If you find that you need the clips a majority of the time, maybe the cables are a good investment.
These attachments are similar to the alligator clips, but the end is a small, spring-loaded hook. This is my preference for measuring values on a circuit board where the only access point is the wire end of a through-hole resistor or diode, barely exposed on the board.
They are limited to very small diameter wires, so they are ideal in situations that are too close-quarters, or too small for the alligator clips.
Mini grabbers, one integrated into the leads and the other is an attachment for the end of an extension cable.
Like the alligators, they can be found as external cables or as dedicated test leads. I even came across a set of end adapters with the grabbers at the end of a flexible 6 inch long tool for the end of an extension lead.
These jaws often look a lot like an alligator clip, but they are opened much like a syringe by squeezing the handle. They are usually much more precise than the alligator ends, made for precision work.
The syringe-style action of a jaw adapter for the end of an extension cable.
In most of my industrial and PCB testing, I haven’t used the jaws very much. When a hands-free, but very secure connection must be made, I wouldn’t always trust the standard alligators - but the jaw adapters will be a very trustworthy connection.
The extension cables open up all kinds of other possibilities. Both ends of these cables could fit into the meter base plug. So the other end is free to connect any of a variety of attachments. You could even mix and match depending on what the specific case called for.
An extension cable with similar connectors on both ends. Either end can connect to the meter, or to the attachments.
I have seen times where someone used normal ‘banana’ cables as an extension to a meter, but I would just add a cautionary note that these cables are not insulated like meter extension leads. The banana style does work, but care must be used, and probably not suited for precision work as the resistance characteristics are not designed for measurements.
A selection of several of the tips that can be added to the end of extension cables to increase capabilities when making very specific measurements.
The tips for the end can be of all sorts - standard test lead ends, or alligator clips, jaws, fine point tips, grabbers, spade terminals (for an even more permanent attachment), and I’m sure there are many others.
Be sure to have the right tool for the right job. If you are going to invest in the tools and learning how to use them properly, then you must also have the proper equipment for interfacing those tools with the real world. Considering that entire sets of leads and accessories can be commonly found for around 20 dollars or less, it’s an easy investment to ensure easy, reliable measurements.