The field current is a programmable parameter that varies depending on the motor size,speed ,capacity, etc. The motor nameplate will give you some information. The Autotune is used to tune the armature. If in fact you can get the Autotune function to work. You had to remove the choke coil and the capacitor-resisters from the Armature loop and then try an Autotune. Later models worked better than earlier ones.