my application is going down after some time of running

Hello Everybody,

         I am Mohamed,  I need to draw a real time gaph in chart. now i face a problem  in draw it.my application slowed automatically when i start to draw the graph.i need your help.i attcahed a application below

 

 

 

i am using 3 button

1.START-used to start the chart

2.STOP-Used to stop the chart

3.Clear-Used to clear the collection of points.when i press the CLEAR button after slowdown of application again the application is working properly for just 1 min after that it will slowed.