The invention provides an online monitoring instrument and method for the concentration and the height of a
urea solution of an automobile SCR
system. Based on the magnetic
coupling resonance principle, the monitoring instrument comprises a high-frequency
signal generation module, a monitoring mode selecting module, a
data collecting and
processing module, a coil design module, a
power module and an automotive
urea tank. Measuring coils are arranged on the bottom side of the
urea tank and arranged in a staggered manner and do not make contact with the urea solution. A self-
resonance mode and a
dislocation impedance matching technology of the coils are adopted, the sensitivity of the self-
resonance frequency and parameters S11 of the coils to the changes of the height and the concentration of the urea solution is improved, and therefore the
signal-to-
noise ratio of detection signals is increased. High-frequency
signal input is conducted on the coil design module through the high-frequency signal generation module, collection and
voltage conversion are conducted on the self-resonance frequency and the parameters S11 of the coils through the
data collecting and
processing module, and the
system development efficiency is improved. The self-resonance frequency of the detection coils is detected so that the height of the urea liquid level can be achieved, and monitoring of the urea concentration is achieved by detecting the parameters S11 of the coils.