How to measure Overshoot in PicoScope 7

What is Overshoot?

An overshoot is a short term spike or transient in a waveform which rises above the Top or drops below the Base levels of a waveform. See Top And Base Measurements article for definitions of Top and Base. Typically an overshoot occurs at the top of a fast rising edge or at the bottom of a fast falling edge, like we see in a square wave.

An overshoot on a rising edge will typically rise for a very short time (relative to the pulse width) above the Top level then may oscillate or ‘ring’ with reducing amplitude above and below the Top level, until finally settling at the Top level. This is called a Positive overshoot.

Similarly, an overshoot on a falling edge will typically fall for a very short time below the Base level then oscillate about the Base level until finally settling at the Base level. This is called a Negative overshoot.

The following screenshots illustrate these two types of overshoot:

positive and negative overshoot diagram

Positive Overshoot

The Positive overshoot measurement measures the difference in the Maximum and the Top as a percentage of the Amplitude and so the calculation is (Maximum – Top) / (Top - Base) x 100.

Negative Overshoot

The Negative overshoot measurement measures the difference in the Base and the Minimum as a percentage of the Amplitude and so the calculation is (Base - Minimum) / (Top - Base) x 100.

Automated Measurement

Setup and configuration

The Positive and Negative overshoot measurements can all be found in the Amplitude category of measurements. After adding the measurement, it will default to measure the whole trace but can be further constrained to only measure between the time rulers, the cycle at ruler 1 or the cycle at ruler 2 using the settings popup.

These screenshots show where these measurements can be found within the application and the settings popup window used to configure the area to measure:

Overshoot automated measurement selection

overshoot measurement area popup

Interpreting results

Positive and Negative overshoot measurements results are shown in their own respective measurement lozenge in the Measurements viewport. By default the measurement is calculated over the whole trace but this can be changed to other options selected in the settings popup which is accessed from the measurement lozenge itself. The measurement lozenge also provides other statistical calculations about the measurement, e.g. maximum, minimum, standard deviation, mean and number of measurements taken.

The following screenshots illustrate both the Positive and Negative overshoot measurements:

Calculation and algorithm

The Positive overshoot measurement is calculated as the difference in the Maximum measurement and the Top measurement as a percentage of the Amplitude, i.e.  (Maximum – Top) / (Top - Base) x 100.

The Negative overshoot measurement is calculated as the difference in the Base measurement and the Minimum measurement as a percentage of the Amplitude, i.e. (Base - Minimum) / (Top - Base) x 100.

See Top, Base and Amplitude article for details on the Top and Base algorithms.

Math channel

The Positive and Negative overshoot Math channels use the same calculation algorithm as the Positive and Negative overshoot measurements, that is (Maximum - Top) / (Top - Base) x 100 for Positive overshoot and (Base - Minimum) / (Top - Base) x 100 for Negative overshoot. Like other Math channels, the result is calculated per cycle rather than for the whole trace. The Maths channel waveform will therefore move up and down to follow any changes in the main waveform.

Note that the Maths channel waveform may not start from the very start of the graph if it can’t find a whole cycle at the start. Likewise for the end of the graph where the Maths channel waveform may fall short if it can’t find a full cycle at the end.

To configure a Positive or Negative overshoot Math channel we use the Math channel creation Wizard, available from the Math channels options panel. Selecting the + button on the Math channels panel will open the Wizard to Add a new Math channel.
 

The Positive and Negative overshoot Math channel options are found in the Scientific functions section of the Formula page (first page) of the Wizard. Simply select the +overshoot or -overshoot channel as required, then select the source channel from the available Channels, e.g. A, B, C and D as shown in the screenshot shown below:

An example of a Positive overshoot Math channel waveform is shown below. It is showing a value of around 19%.
 

Note that when creating the Math channel, its range defaults to 0 - 100%. This can be seen on the 2nd page of the math creation wizard:


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