how to compare a measured voltage signal with a reference signal which is a function of time in simulink?

i am working on designing a grid connected solar PV system. the problem is that i have to compare the measured grid voltage with a LVRT curve shown in picture. this comparison should start only when the measured grid voltage is below a certain threshold value. in other words, the task can be sumarised as:- measure grid voltage if grid voltage is found to be less than a certain value, then start comparing it with the LVRT curve. if it is below LVRT curve at any point in time, then trip the system. i have tried to program it using timer function, but it does not support code generation. can somebody suggest a simple solution or where i should look for solution?