METHOD AND DEVICE FOR TESTING A LIQUID

摘要

The invention relates to a measuring device (2) adapted to testing a liquid (4) used as reducing agent in connection with exhaust cleaning for exhaust gases from a combustion engine. The device comprises a temperature sensor (6) adapted to measuring the temperature in the liquid and an acoustic velocity measuring unit (8) adapted to measuring the acoustic velocity in the liquid. The temperature sensor is adapted to determining a first temperature T1 for the liquid and to delivering on the basis thereof a temperature signal (12) to a calculation unit (10); the acoustic velocity measuring unit (8) is adapted to determining a first acoustic velocity v1 for the liquid at the temperature T1 and to delivering on the basis thereof an acoustic velocity signal (14) to the calculation unit (10). The temperature sensor (6) is further adapted to determining a second temperature T2 for the liquid and to delivering on the basis thereof a temperature signal (12) to the calculation unit (10), which is adapted to calculating the absolute value of a temperature difference ?T between T1 and T2, i.e. ?T = ?T1-T2 ?, and to comparing ?T with a predetermined threshold value TTH. If ?T exceeds TTH, a control signal (16) is delivered to the acoustic velocity measuring unit (8) to determine a second acoustic velocity v2 for the liquid at the temperature T2 and to deliver on the basis thereof an acoustic velocity signal (14) to the calculation unit (10), which is adapted to comparing v1 and v2 with respective first and second velocity reference values vref1 and vref2 for a reference liquid at the respective temperatures T1 and T2. On the basis of the result of the comparison an indicating signal (18) is generated to the effect that the liquid is approved if the measured values v1 and v2 are within approved velocity ranges for the reference values, but not approved if v1 and v2 are not within a said approved velocity ranges.