The GQS 400 is a compact gas analysis device with a microthermal sensor in combination with a critical nozzle. From the signals of the sensors the quantities calorific value, relative density, methane number and Wobbe index can be determined by a correlative method. The GQS400 is suitable for fuel gases with calorific values between 7.8 kWh and 14 kWh. It operates without carrier gas or other auxiliary gases. Due to the short measuring cycle time of approx. 30 seconds, the GQS 400 is perfectly suited for control tasks.