title: How to detect a sudden change in a time series plot in Pandas
body: <p>I am trying to "detect" a sudden drop in velocity in a series and I'm not sure how to capture it. The details and code are below:</p>
  
  <p>This is a snippet of the Series that I have along with the code to produce it:</p>
  
  <pre><code>velocity_df.velocity.car1
  
  Index   velocity
  200     17.9941
  201     17.9941
  202     18.4031
  203     18.4031
  </code></pre>
  
  <p>Here is a plot of the entire series <a href="https://i.stack.imgur.com/SqXjS.png" rel="noreferrer"><img src="https://i.stack.imgur.com/SqXjS.png" alt="enter image description here"></a></p>
  
  <p>I'm trying to detect the sudden drop from 220 to 230-40 and save that out as a Series that looks like this:</p>
  
  <pre><code>Index   velocity
  220      14.927
  221      14.927
  222      14.927
  223      14.927
  224      14.518
  225      14.518
  226     16.1538
  227     12.2687
  228     9.20155
  229     6.33885
  230     4.49854
  </code></pre>
  
  <p>I'm just trying to capture an approximate range when there is a sudden decrease in speed so as to use other features.</p>
  
  <p>If I can add any additional information, please let me know. 
  Thank you!</p>