How to Use an Oscilloscope to Measure DC Voltage

Oscilloscopes are machines that measure and show voltage signals over a period of time. They are used to monitor the changes in an electric signal over time.

Voltmeters, also known as voltage meters, are used to measure the potential difference between two points in an electronic circuit. Now, you might be thinking, can we use an oscilloscope as a voltmeter?

Well, if your oscilloscope is a Cathode Ray Oscilloscope (CRO), then the answer to this is yes, it can be used to measure potential differences between two points just like a voltmeter. But there are some factors you should be considering if you plan to do that. They are discussed below.

Why Oscilloscope instead of the Voltmeter?

Voltmeters have an analog display and can be considered as old fashioned. It is quite hard to pinpoint the voltage at short intervals, so it is difficult to monitor the voltage using a voltmeter.

On the other hand, oscilloscopes have a digital display, and it shows us the instantaneous voltage per second.

These instant responses are moreover displayed in a graphical manner, which makes it very easy to follow or find a trend.

Some oscilloscopes have more than one channel so you can connect two or more devices at the same time and compare the results.

Click here to check budget oscilloscope review guide.

Factors for Consideration

Nowadays, Digital Storage Oscilloscopes (DSO) are more widely used and popular compared to Cathode Ray Oscilloscopes (CRO). DSOs are the digitalized versions that offer more functions and are more preferable over CROs. So chances are even if you do own an oscilloscope, it is a DSO rather than a CRO.

CROs are generally more precise with an almost infinite input resistance; thus, they can be used as voltmeters. However, DSOs are simpler and more adequate to use unless you need to see the waveform, which in the case of measuring the potential difference between two electric points, is important.

Moreover, using CROs as a voltmeter is not very practical, and it is easier to just use a digital voltmeter instead. The only reason a CRO might be used as a voltmeter is as an experiment for students to get acquainted with the device and learn the basics of how it works. In the next section, I will briefly explain how to that.

Related Review: under $500 Oscilloscope Review

Procedure for a Simple Classroom Test

Procedure for a Simple Classroom Test

Note that we will be using a voltmeter as well in order to check validity since this is only a practice test. You will need the following things –

  • Three 1.5 Volt cells which are connected in a series
  • A voltmeter of 0-5 volts
  • A cathode-ray oscilloscope
  • A low voltage supply
  • Two leads, 4 mm measurement
  • Two leads, 4 mm measurement

How to Use Oscilloscope to Measure Voltage

Step 1: Setting up

Set up the oscilloscope with the gain as 1 volt per division; set the time-base off and switch to DC on the AC/DC switch.

Step 2: Connecting

Connect the CRO’s input across one of the cells and adjust the gain to make the deflection one division on the graticule. After that, connect the voltmeter in parallel to the oscilloscope across the cell.

Step 3: Testing

Now, connect across two cells & then across three cells and test the deflection on the oscillator’s screen. After you are done observing, do the same thing again but reverse the leads beforehand to observe the deflection across the three cells in the opposite direction. The CRO will act as a voltmeter here.

Step 4: Retesting

Disconnect the cells and reconnect after changing the output of the power to 2 volts. Do the same thing with 4 volts and 6 volts as well. In all of these observations, the CRO will act as a voltmeter; this will help you better understand the CRO and how it works.

Step 5: Final Results

Switch on the time-base of the CRO (1 ms per division) to show the trace spread out on the screen. This will show whether the power supply provides a steady voltage or not, which is the result of your experiment.

How to Measure DC Voltage Using the Oscilloscope

Below is the detailed procedure of how you can measure the DC voltage using an oscilloscope.

  • Turn the machine on.
  • In the front panel, there is a trigger section and switches labeled AUTO, NORM, etc. You have to switch on AUTO.
  • There is a horizontal section in the front panel. Among the many switches, there is a MAIN TIME/DIV knob. You have to set this to 0.1mS.
  • There is also a vertical section in the front panel with switches labeled as CH1, CH2, DUAL, ADD. Turn the switch to DUAL.
  • Around the CH1 (channel 1) area of the front panel, there are more switches labeled AC, GND, DC. You have to switch on the switch labeled DC.
  • Turn the CH1 VOLT/DIC knob to 1V.
  • Adjust the CH1 POSITION KNOB so that the trace is lined up at the bottom on the grid. You can see this happening on the screen as the green line will be moving as you adjust the knob. When it is at the bottom, we can say that it is the zero point for CH1.
  • Repeat the above steps for the CH2 (channel 2) area.
  • Finds the switches on the oscilloscope’s probes and set them to x1.
  • Connect the alligator clips on your circuit.
  • Decide the points on your circuit you want to measure the voltage from and connect probes there.
  • Measure the voltage fluctuations from the display.

Conclusion

That’s all, folks! The experiment ends here. I hope you were successful in using a CRO as a voltmeter. I hope you got the answer you were searching for. Thanks for reading.

Leave a Comment