The scope voltage and time settings determine the size of our waveform on the scope screen. We can zoom out, displaying more waveform at a smaller size, or zoom in, magnifying a portion of the waveform for closer analysis. Vertical size is controlled by the voltage adjustment; horizontal size by the time adjustment.

This month, we look at voltage adjustments.

Scope Voltage Settings

Digital scopes commonly use push buttons or rocker switches to assign voltage and time values to grid divisions. Our generic DSO has a rocker switch that allows us to increase or decrease the voltage assigned to each division.

DSOs display the Volts/Division numbers on screen, digitally. Here we see that Channel A is DC coupled, and that the Volts/Div is set to 2 Volts/Division. Channel B is turned off.

 

The list below shows a range of Volt/Div adjustments we might see on a scope, and the maximum voltage that can be displayed on screen for each setting. The range of adjustment and individual voltage levels depend on the scope design. The maximum voltage that can be displayed is calculated by multiplying the number of vertical divisions times the voltage setting, e.g. 8 divisions x 2 volts = 16 volts.

 

 

V/DIV and Screen Display

Volt/Div Setting	Max Voltage on Screen
.050V (50mV)	400 mV
0.1V (100mV)	800 mV
0.2V (200mV)	1.6V
0.5V (500 mV)	4V
1V	8V
2V	16V
5V	40V
10V	80V
20V	160V
50V	400V
100V	800V
200V	1600V

 

Volts and Millivolts

Scope voltage is displayed in volts and millivolts.

To better understand millivolts, divide one volt into 1000 equal pieces. Each "piece" equals one millivolt.

• There are 1000 millivolts in one volt.

• 500 millivolts equals 1/2 volt

• Traditional zirconia style oxygen sensors operate in a 0-1 volt range. The waveform in the illustration above shows voltage activity from an oxygen sensor. The waveform is created as the voltage generated by the sensor fluctuates up and down to indicate changes in the amount of exhaust oxygen. The computer uses this input to adjust fuel delivery.

 

Voltage Adjustment

Voltage adjustments allow us to zoom in and out to con­trol how much of a waveform is displayed on screen.

Here is a repetitive waveform. We have shown the wave­form extending beyond the scope window on both sides. This illustrates that the waveform is continuous.

 

Right now, our scope is adjusted to a 10 Volts/Division setting. If we count the number of divisions the signal rises, we see that the signal's vertical voltage spike rises 6 complete divisions. Mul­tiplying volts times the number of divisions tells us the spike's amplitude.

6 divisions x 10 volts = 60 volts

 

In this instance, a Volts/Div set­ting of 10 volts allows us to fit the entire height of a waveform with an amplitude of 60 volts on the screen.

 

Zooming in by Decreasing the Volt/Div Settings

Sometimes we want to zoom in for a closer look at a waveform. It's like putting the wave­form under a magnifying glass.

To zoom in on an image, decrease the voltage per division setting.

Here we are zooming in to take a closer look at part of the waveform.

Scope voltage is set to 5 Volts/Div.

• At this setting, we can fit a waveform on screen with a maximum 40 volt ampli­tude (8 vertical divisions times 5 volts = 40 volts maximum dis­play).

• Our waveform has an amplitude greater than 40 volts, so part of the waveform does not fit on screen.

• Right now we don't need to see the entire waveform. Instead, we want to zoom in closer to take a measurement in the area visible on the screen. It's like viewing something under a magnifying glass. We see less of the object, but the magnified area is enhanced and contains more detail.

Practice, Practice, Practice
Get your scope out and start sampling signals. Adjust the voltage per division setting and see how it changes the appearance of the waveform on the screen.

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