A sensor unit adapted to measure a mass flow rate of a liquid hot-melt adhesive , comprising at least: a flow channel for the hot-melt adhesive , a first temperature measurement device positioned at a first position in the flow channel for measuring a temperature of the hot-melt adhesive at the first position in the flow channel , a second temperature measurement device positioned at a second position in the flow channel and a heating device assigned to the second temperature measurement device for heating the second temperature measurement device , the second temperature measurement device being used for measuring a second temperature at the second, heated temperature measurement device , and a control unit for controlling the heating device and for measuring the mass flow rate, which is designed and configured to adjust the temperature of the second temperature measurement device to a value and determine the heating power for heating the second temperature measurement device and to calculate the mass flow rate in the flow channel , characterized in that the sensor unit comprises: a sensor block , wherein 1) the first temperature measurement device and the second temperature measurement device are mounted on the sensor block ; 2) the first temperature measurement device and the second temperature measurement device are each planar and flat; and 3) the first temperature measurement device and the second temperature measurement device are arranged substantially parallel to each other in the flow channel . a flow channel for the hot-melt adhesive , a first temperature measurement device positioned at a first position in the flow channel for measuring a temperature of the hot-melt adhesive at the first position in the flow channel , a second temperature measurement device positioned at a second position in the flow channel and a heating device assigned to the second temperature measurement device for heating the second temperature measurement device , the second temperature measurement device being used for measuring a second temperature at the second, heated temperature measurement device , and a control unit for controlling the heating device and for measuring the mass flow rate, which is designed and configured to adjust the temperature of the second temperature measurement device to a value and determine the heating power for heating the second temperature measurement device and to calculate the mass flow rate in the flow channel , characterized in that the sensor unit comprises: a sensor block , wherein 1) the first temperature measurement device and the second temperature measurement device are mounted on the sensor block ; 2) the first temperature measurement device and the second temperature measurement device are each planar and flat; and 3) the first temperature measurement device and the second temperature measurement device are arranged substantially parallel to each other in the flow channel . 1) the first temperature measurement device and the second temperature measurement device are mounted on the sensor block ; 2) the first temperature measurement device and the second temperature measurement device are each planar and flat; and 3) the first temperature measurement device and the second temperature measurement device are arranged substantially parallel to each other in the flow channel . <EOS>