What OL Means On A Multimeter ( #1 Ultimate Guide)

Before we get into the details on what OL means on a multimeter, please have a read of the table below.

Why This Article On What OL Means On A Multimeter

The term OL is very common in the measurement tool space, especially on a multimeter. You will often hear it when operating and working with seasoned professionals, electronic practitioners and electricians. They will say things like “The meter reading is OL” or “not getting much, its giving me an OL”.

If you are confused and thinking, what on earth does OL even mean, then no worries. This guide will unpack these points for you and give you a lot more confidence when reading your multimeter. 

I have made it a point within this guide to really explain it in a bit more detail so you are technically equipped on all the parameters that actually cause the “Open Loop” reading on a multimeter.

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What You Need To Know About What OL Means On A Multimeter

The OL (Open Loop) on a multimeter practically refers to an open circuit. This means that there is practically no current flowing between the terminals of the multimeter. Hence the name Open Loop.

In reality this happens when the resistance is so large between the two terminals such that the multimeter can no longer measure this value. You will often find this exact resistance within the technical datasheet of your specific multimeter.

Just to further hammer the point above – the physical limitation of resistance measurement for your specific multimeter will trigger an open loop or OL reading on the LCD screen.

For example if you look at the Fluke 87-V Industrial Multimeter you can easily see that the maximum resistance it can measure is 50 MΩ. Anything above this and the meter will read “OL”.

How Does A Multimeter Measure Resistance And Why Do The Limits Differ?

You might (or may not) be surprised that a multimeter is actually a current measuring device and via the use of the famous ohms law as seen below. What is very important to pick up on this equation it the fact that if you have two of the three parameters you can easily determine the other.

V (Voltage) = I (Current) x R (Resistance)

This formula practically explains how voltage, resistance and current are related, and more importantly for our specific us case showing the direct linear relationship between resistance and current.

So back to the previous point. The multimeter is a current measuring device. This current gets generated from the battery and travels through the test leads when you are measuring resistance.

The actual quantum of moving charge (current) is minimal but enough to determine whether the multimeter is reading an Open Loop or there is some form of continuity.

If the resistance between the two test leads is greater than the multimeters maximum resistance, then the meter will return and OL.

That’s that – quite simple.

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The Difference between OL and Continuity On A Multimeter

Given that the measurement of OL is well defined and adequately understood, there still remains the small issue of understanding key differences between the OL measurement and continuity.

Keep reading, as I explain these below.

Continuity is practically the opposite of the open circuit (represented by the OL). In a continuous circuit all components of the circuit are interconnected creating continuous loop.

What this basically means, is that when measuring resistance via your multimeter, the multimeter will run an internal calculation to ultimately determine a minimum resistance value.

Once the actual resistance goes below this value (in most high end multimeters we are looking at something along the lines of around 20Ω). Then the multimeter will return a reading of continuity.

If you have been using multimeters for some time, this measurement is often characterized by the famous audible beeping sound.

Furthermore, continuity is a fantastic parameter to be used when troubleshooting circuits. Especially when operating on electronics.

As I reiterated above. This exact minimum value of resistance can be determined for your specific multimeter as read from the individual datasheet.

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Step by Step Guide to determining OL on Multimeter

Step 1: Setup your multimeter to measure resistance

Most multimeters have a know, however more and more these days there are meters that utilize digital touch buttons. Whatever the manufacturers preference, setup your multimeter in such a manner as to ensure that you are measuring resistance.

Step 2: Install the test leads

Once you have completed step one, it is time to install the test leads. Add the black lead into the common terminal typically labelled “COM” and the red lead into the positive terminal.

This positive terminal also is typically labelled with a “V/Ω”.

Step 3: Measure circuit

Now that everything is setup you can go ahead and test whatever circuit you wish.

What I typically do to ensure that the meter is actually functioning correct, I connect the two leads together. Checking for a beeping sound and continuity. If the multimeter is continuous – then I know it is functioning.

You can then go ahead and test your specific circuit. If you see a resistance reading then the circuit is not an open loop and there is some form of continuity.

If the circuit you are measuring has a resistance that is in fact above the measurement tools threshold, then it will return the famous “OL”.

That is that.

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Final Thoughts On What OL Means On A Multimeter

I hope after reading this article you feel better equipped in understanding what the OL means on your multimeter. Also how to go about using it effectively.

As I have shown you – OL without fully grasping and understanding continuity does not really make sense. Hence why I also provided a broad explanation and quick step by step guide to help you practically use your new found knowledge.

All the best and happy measuring.