Abstract: In order to determine a property of a given substance, the latter and a reference substance are alternately fed, by a suitable pump, for example, into and through a receiver in which each substance remains for a given time increment before the other substance is delivered thereto. The receiver is permeable to predetermined radiation which travels through the receiver and the substance therein to be absorbed to different extents by the given substance and the reference substance. The radiation travelling beyond the receiver is measured to derive therefrom alternate measurements resulting from the radiation travelling through the given substance and the radiation travelling through the reference substance, this radiation being derived from a suitable source which directs the radiation through the receiver and the substance therein. These alternate measurements are compared to determine the property of the given substance.

Abstract: An arrangement for measuring conditions within a cement kiln in which the metallic body of the kiln is used as a wave guide for radio waves used for the measurement. An antenna with radio frequency energy applied thereto, runs through the kiln, and measuring antennas are located at predetermined points along the length of the kiln. The prevailing field strength measured by the measuring antennas is indicative of the conditions, particular temperature, which prevail within the kiln. Each of the measuring antennas may lie in a plane perpendicular to the kiln access, and a stationary link is inductively coupled to each measuring antenna. The stationary link travels around the kiln in a plane perpendicular to the axis thereof.