Method to determine or monitor the amount or the distribution of additional material present in a flow of a flowable substance

A method to determine or monitor the amount or distribution of additional material present in a flow of a flowable substance, said method comprising the steps of

• providing a flow of a flowable substance in an open channel, said flow of said flowable substance comprising bulk material comprising concrete or mortar and additional material comprising magnetic material;
• determining the volume flow of said flow of said flowable substance at one or more detection points X along said flow of said flowable substance;
• determining a signal caused by said additional material present in said flow of said flowable substance at one or more detection points Y along said flow of said flowable substance, said signal being proportional to inductance or magnetic properties, the inductance or magnetic properties being proportional to the amount of said additional material present in said flow of said flowable substance passing said one or more detection points Y, said one or more detection points Y being the same as or different from said one or more detection points X;
• converting said signal caused by said additional material present in said flow of said flowable substance into a signal per unit of volume of said flow of said flowable substance.