How to add variable to dynamic parameter file

Hi,

I want to include the following dynamic parameter file

pset paramset{

time     temp

0          25

10m     70

20m     temp_xxx

}

The variable temp_xxx has been created in variable of the test. 

But when i run the sim,  it reports the error about temp_xxx. " ERROR (SPECTRE-8525): The parameter 'temp' in paramset 'pset' cannot be of type string. Redefine the parameter and rerun the simulation. "

One the other hand, i can directly input those content in the dynamic parameter setting in the tran sim. There is no problem about temp_xxx. 

Anyone knows some clue?

BR