Using arduino with simulink to acquire an analog signal

I tried to acquire an analog signal (sinusoidal shape with a frequency of 50Hz) using MATLAB/SIMULINK and an analog input pin of ARDUINO MEGA 2560.
The model was run in external mode.
However, the visualised signal does not match the original signal
Thank you for your help
Best regards

However, the visualised signal does not match the original signal

Nor did you provide any code. Good luck.

Were you sampling it at Nyquist frequency or above in your Simulink model?