Measuring Frequency With a Digital Multimeter

We have written about using regular Digital Multimeters (DMMs) to measurements common things such as Voltage, Current, Resistance and much more. Those post can be checked out here or here!

But in this post we will look deeper into an often overlooked, but quite handy function that’s part of many DMMs. Namely:

Frequency Measurement

Introduction

As earlier, will we be using a Keysight U1221A multimeter to show you this feature.

First we have to configure our DMM for Frequency Meassurement. How to do this depends on the DMM you are using, but on the U132A we are using here we have to:

  • Turn the rotary wheel to ~V (Hz in orange)
  • Press the orange button to change over from ~V to Hz
  • The display will show Hz when this is done correctly

Setting up the external signal

We used an old signal generator (GW GFG-8050) to create a rectangular pulse train.

The frequency we used varied, but the Vpp was always ~3 V.

We confirmed the signal on a regular oscilloscope and it looked like this:

To get this signal into the multimeter we used a regular BNC cable from the signal generator and a “Female BNC to Banana Plug Adapter”.

Results

First we applied the 20.022 kHz, and the result on the multimeter looked like this:


Going out of specifications

As you can read in the U1232A datasheet (here), is it specified an operating range form 99.99 Hz to 99.99 kHz. But what happens when we go outside this?

We started with turned down the frequency to under 2 Hz and the DMM outputted:

This was spot on what the signal generator said it was outputting, but how high can we go?

When we applied higher frequency than shown in the image above, the multimeter started showing lower frequency than the actual frequency.

But still: Way outside the specified operating range! So happy here 🙂

Final words

As we saw in the latest picture the DMM had a challenge keeping up with a signal higher than ~200 kHz. But that was no surprise. This is way beyond the specified operating range.

Within that range it was quite spot on!

But is frequency measuring useful in real life?

YES!

One of the most obvious one is measuring the AC frequency of your wall outlets.

In an upcoming post we will show you a project where multimeter frequency measurement is an important part!

So stay tuned 🙂

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