Basic Oscilloscope Usage

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BK Precision 2120B Oscilloscope

This article aim's to provide a user with a basic intuition of how to use our oscilloscope. It will not be fully exhaustive of everything possible with the device but you should hopefully be able to help you get started.

Oscilloscope Breakdown

The BK Precision Oscilloscope in the lab is a dual trace scope. This means that you can view up to 2 signals at time as long as the signals themselves are not faster than 30 mega hertz. (For reference the clock frequency of an arduino uno is 16 MHz which means you view pretty much anything that the uno spits out)

There are several knob's and switches on the scope but if you know a few basic concept's of what the scope is doing it will not be overwhelming to figure out. The scope itself is just a window that let's you view how voltage change's over time.

Usually, all you need to worry about is making sure the timing, voltage, and triggering is configured.

Timing

So for example if we have a waveform we want to see that is about 1KHz. Then first determine the we know that at 1KHz frequency then one cycle is about 0.001 seconds or 1 millisecond. (More info and Frequency to Period Converter)

We can then turn the knob marked TIME/DIV to match the number we calculated (1 millisecond) to set each cell in the grid to represent 1 millisecond and since the display is a 10x8 grid. We will be able to see 10 milliseconds of the waveform.

Voltage

Next, we need to set the voltage per cell for the grid. Remember, there are 2 channels so we have to first make sure that we have selected to view the right channel which is marked as a switch on the oscilloscope marked "VERT MODE" The options for the switch are:

  1. CH1 - Meaning view channel one only.
  2. CH2 - Meaning view channel two only
  3. DUAL - View both channel's one and two
  4. ADD - View what happens when you add the inputs to channel's one and two together.

Once you have selected the right channel use the VOLT/DIV to set how much voltage each cell in the grid will represent vertically.

So for example if we set this knob to 1 volt then since the grid is 8 cells tall we will be able to see a signal around 8V peak to peak.


Triggering

Intuition

Something that confuses a lot of people is triggering.

When talking about triggering, we are just telling the oscilloscope to look for a particular event, that is, for the waveform to transition from low to high or high to low to draw it. This is helpful because as long as the waveform is periodic (or in other words always repeats after a certain amount of time) it will look as if the oscilloscope has taken a picture that doesn't change on the display. If the triggering is setup incorrectly, the oscilloscope won't know exactly when to start drawing the waveform and it will appear as if the waveform is erratic.

Here is an example of correct triggering of a sine wave

Here is an example of triggering failing on a sine wave

Setup

To actually setup the triggering. In the top right corner of the scope, there is a section for triggering. The main things to consider are the knob labeled TRIG LEVEL and the lever labeled SOURCE.

The first thing to consider is to make sure the SOURCE is setup correctly. This is simply selecting which channel the oscilloscope is listening on for the trigger. So if we have an input going into channel 2 and not channel 1 but we are listening for a trigger on channel 1. We will obviously never get it to trigger correctly.

Then the next question to ask once we know what channel we are listening on is, what should the voltage threshold be for the trigger? This is what the TRIG LEVEL knob indicates. When it is being adjusted, you should be able to see a thin green line moving up and down the screen as it searches for the waveform. If not, just roll the knob up and down until the waveform stops being erratic.