The Multimedia Mul-ticast Channel

A sensing apparatus is disclosed for measuring the concentration of gas in a blood sample. The sensor includes a temperature measuring surface centrally enclosing a sensor head for measuring the indicator concentration. The temperature measuring surface has a low heat capacity and is electrically heated to a constant temperature by means of an electrical control device. A ring of a material having good heat conductivity is provided to form a measuring tray having a close heat contact with the temperature measuring surface. The measuring tray is in the form of a reservoir for the blood. The bottom of the reservoir is positioned adjacent the sensor head being separated only by a gas permeable membrane.