Dear Maham,
After installing MATLAB/Simulink there is no 'NIT SIT' block. However you can download this block from this NI website.
If you like to connect a sensor to your simulink model, you could also use a microcontroller (i.e. Arduino uno) and install software to connect the arduino to Simulink. At this Mathworks website, you can read how to do this.
For a complete overview which possibilities there are to connect hardware to MATLAB/Simulink, you can find here: www.mathworks.com/hardware-support/home.html
Kind regards, Christiaan van Ommeren
