Problem in Reading Excel file for looking at threshold values.

I Have some data in my excel and i want read them as below:
look for the first value in ch1 above the criteria and name it as t1.
Look for the last value in ch1 above the criteria and name it as t2.

Here I am using my tcreteria as 300V.

I have attached by excel sheet..so please kindly help me as soon as possible.

Thank you.