The invention discloses an external ultrasonic level gauge with a sound velocity self-
calibration function. A DSP and an
OLED display screen are connected with a temperature sensor, the DSP is connected with an ultrasonic driving and receiving module, and the ultrasonic driving and receiving module is connected with a
storage tank to be detected through an ultrasonic
transducer. The measuring method includes the steps that (1), a measuring probe and a self-calibration probe are externally attached to the bottom and the wall of a tank body to be detected respectively; (2), the DSP is started, the ultrasonic level gauge is in a double-probe measuring mode, reference sound velocity is directly calibrated through the self-calibration probe, or the reference sound velocity is indirectly calibrated by using a temperature and sound velocity data table; (3), after the speed velocity is calibrated, a blind area position is detected; (4), an ADC module is used for collecting an ultrasonic
signal to obtain wave backing data of the medium to be detected, and round tip time of ultrasonic
wave transmission is calculated; (5), according to the reference speed velocity and the
transmission time, the height of the liquid level is calculated; (6), a calculated liquid level value is used for stabilizing the liquid level; (7), the display result and 4 mA-20 mA output of the liquid level of the
OLED display screen are updated, and the latest liquid level value is stored in FLASH.