Export equivalent circuit for not nominal design does not work

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Using the example provided on the PyAnsys website to simulate striplines with Q2D, I cannot export the equivalent circuit for design variations that are not nominal.

The example is on this page

I am just adding the following command 

q.export_equivalent_circuit(file_name='test.ckt', 

              sweep='sweep1',

              variations=['sig_bot_w:75um','sig_gap:100um'],

              matrix_name='diff_pair')

But I get the error: "pyaedt ERROR: Provided variation value doesn't exist."

How should I define the variations parameters? It is not clear to me.

Thanks,

Nicolas