The present invention discloses a ultrasonic method for indirectly measuring a pressure of a cavity of an injection molding machine, comprising: emitting ultrasonic wave to each pull rod along an axial direction of the pull rod respectively at the same time, detecting an ultrasonic wave echo time difference of each pull rod, and obtaining an average pressure inside a cavity of the injection molding machine. By the detection method and detection device of the present invention, the pressure inside the cavity may be detected in a certain state, the pressure inside the cavity in the injection molding process may be detected in real time, and the detection process is simple and the accuracy is high.

A waterproof pressure sensor includes a pressure detection element, a cavity package configured to be provided with a recess in which the pressure detection element is mounted and an edge provided around the recess, a cover member attached to the edge of the cavity package and to be provided with a pressure introducing hole having a diameter smaller than a diameter of an opening of the recess in a plan view at a position overlapping the recess, and a gel agent configured to be provided in the recess, in which an exhaust portion is provided at the cover member at least on the recess side, the exhaust portion being capable of discharging air in the recess to the outside when the gel agent is injected from the pressure introducing hole into the recess, and the exhaust portion is filled with the gel agent.

The present invention discloses a ultrasonic method for indirectly measuring a pressure of a cavity of an injection molding machine, comprising: emitting ultrasonic wave to each pull rod along an axial direction of the pull rod respectively at the same time, detecting an ultrasonic wave echo time difference of each pull rod, and obtaining an average pressure inside a cavity of the injection molding machine. By the detection method and detection device of the present invention, the pressure inside the cavity may be detected in a certain state, the pressure inside the cavity in the injection molding process may be detected in real time, and the detection process is simple and the accuracy is high.