A method and an apparatus of obtaining measurement data from a chemical process in a mass in a space, such as the charge in a blast furnace, is disclosed where the mass passes through the space from an inlet to an outlet and chemical and/or mechanical change in the mass takes place as it passes through the process. Sensors implemented as individual, unconnected units are mixed into the mass at the inlet, each sensor being equipped with a transmitter of acoustic or electromagnetic type, and with one or more sensing means connected to the transmitter for sensing the properties to be measured. The transmitter sends signals with information on the properties detected by the sensing means. Reception means for taking up acoustic or electromagnetic signals are placed outside the space with spreadout placing over the defining surface of the space. The position of the sensors inside the space is calculated with guidance from a property such as signal strength, time position, field direction or the like, of the signals sent by the different sensors and received wirelessly by said reception means. The properties of the surroundings measured by the sensing means of the sensors are finally presented for each sensor as measurement data for the calculated position of the sensor.