Tars produced during the thermal conversion of coal or especially biomass is one of the major obstacles for the application of gasification systems. They limit the use of the producer gas in engines or turbines or, in further processes like in methanization or conversion to other secondary fuels or chemicals, without further gas cleaning. The determination of the tar content with conventional methods is very time consuming and does not allow continuous online monitoring of the gas quality. One approach to avoid these drawbacks is an automatic system developed at the University of Stuttgart that monitors the tar concentration in the producer gas online and semicontinuous during the gasification process. The technique is based on a flame ionization detector (FID) difference measurement of the hydrocarbons in the producer gas, where the condensable hydrocarbons—the tars—are condensed on a suitable filter material. This work shows the further development of the measurement technique, the choice of a suitable tar filter material for the underlying difference measurement, and a first verification of the system with real producer gas at a 20 kWth bench scale gasifier.