Run and Stop samplingthread on qwt Oscillocope

hi everyone !!
I want to control the start of samplingThread on Oscillocope example
I 've created in MainWindow datei the Button "Run" and function startThread();

then I connected in MainWindow datei the button Run and the function startThread like this
connect(run, SIGNAL(clicked()), SIGNAL(startThread()));

finaly in Main datei I've Connected
window.connect( &window, SIGNAL( startThread( ) ),
&samplingThread, SLOT( start() ) );

now when I push on my Button "Run" , the curve (signal)does not appears anymore continuously but periodically
normally the Button Run is just just to trigger the beginning of the Thread

what is wrong ?
any help would be appreciated