Measuring system consisting of a measuring device for measuring the flue gas components of a gas sample with a control unit and a measuring gas probe for taking the gas sample in a hot, dust-containing gas atmosphere, wherein the measuring gas probe comprises - a flange for placing the measuring gas probe on a furnace inlet chamber containing the gas to be measured, - a tubular, coolant-cooled probe body having a tubular outer wall , a bottom closing one end face and a cover closing the other end face , - with coolant supply and coolant return so that coolant can flow in the interior of the probe body , - a first sampling tube which extends in the interior of the probe body parallel to the longitudinal axis of the probe body and passes through the cover , wherein an end of the sampling tube remote from the cover is bent laterally so that the end is formed as a first sampling opening for gas extraction laterally from the tube outer wall , - a second sampling tube extending substantially parallel to the first sampling tube and of identical construction to the first sampling tube and having a second sampling opening , - whereby the two sampling tubes are cooled by the coolant, - and the sampling tubes pass through the cover for connection to the measuring device , wherein the two sampling tubes of the measuring gas probe are connected to the measuring device via gas lines, characterised in that - that gas shut-off valves are provided for the selective connection of one of the sampling tubes to the measuring device and tube back-flushing devices are provided for flushing the sampling tubes, - and in that the control unit is arranged to control the measuring gas probe in such a way that the gas sample is taken through one of the two sampling tubes and during sampling, the other sampling tube is cleaned by the tube back-flushing device. - a flange for placing the measuring gas probe on a furnace inlet chamber containing the gas to be measured, - a tubular, coolant-cooled probe body having a tubular outer wall , a bottom closing one end face and a cover closing the other end face , - with coolant supply and coolant return so that coolant can flow in the interior of the probe body , - a first sampling tube which extends in the interior of the probe body parallel to the longitudinal axis of the probe body and passes through the cover , wherein an end of the sampling tube remote from the cover is bent laterally so that the end is formed as a first sampling opening for gas extraction laterally from the tube outer wall , - a second sampling tube extending substantially parallel to the first sampling tube and of identical construction to the first sampling tube and having a second sampling opening , - whereby the two sampling tubes are cooled by the coolant, - and the sampling tubes pass through the cover for connection to the measuring device , wherein the two sampling tubes of the measuring gas probe are connected to the measuring device via gas lines, characterised in that - that gas shut-off valves are provided for the selective connection of one of the sampling tubes to the measuring device and tube back-flushing devices are provided for flushing the sampling tubes, - and in that the control unit is arranged to control the measuring gas probe in such a way that the gas sample is taken through one of the two sampling tubes and during sampling, the other sampling tube is cleaned by the tube back-flushing device. <EOS>