Device for online calibration of differential pressure liquid level meter and calibration method

The device comprises a base, a calibration part and a reference part, the calibration part comprises a spring, a displacement transmission mechanism and a limiting plate, the spring is connected with the base, the spring, the displacement transmission mechanism, a supporting column and a mounting platform are sequentially connected, the limiting plate is arranged in the middle of the displacement transmission mechanism, and the displacement transmission mechanism is connected with the supporting column. A limiting plate fixing platform is arranged at the top of the support, a through hole penetrates through the limiting plate fixing platform, and a limiting plate moving groove and a limiting plate clamping groove are formed in the side edge of the through hole. The reference part comprises a test reference supporting rod, a displacement adjusting mechanism and a test reference mechanism, the displacement adjusting mechanism is connected with the test reference supporting rod, one end of the test reference mec