@grompvevo 

I do not get the error with Maple 2024.1. Which version of Maple do you use?

I would be interested in the invariant you intend to use to test solutions. The invariant could be used to test the symbolic solution below as well

pdsolve({pde, v(a, t) = 0, v(b, t) = 0, v(x, 0) = f(x + 5), D[2](v)(x, 0) = -eval(diff(f(x), x), x = x + 5)})

You could of course use this solution, which is independed from any physical context, for tests as well.

@Christopher2222 

Correct. Probes could be a way to plot variables over time. However:

Probes connect to ports of components. In the case of  a sphere contact only two variables are exportet: dummy (which gives an error) and R which is the radius of the sphere.