constraining dependent variable

Good day:

I am trying to find the most effective method of implementing a constraint on a dependent variable.

I am solving a classical diffusion equation (using Equation based modeling)of concentration 'c' and I do not want my variable 'c' to exceed some value 'cmax' on the entire domain I am modeling on.

What is the most effective way that COMSOL allows this to be done?

Thank you for any help given in advance.