In-pipe diameter measuring device

The invention relates to the technical field of measurement, and discloses an in-pipe diameter measuring device which comprises a cart, a controller is fixedly connected to the cart, a motor is fixedly connected to the telescopic end of a second electric push rod on the cart, and an output shaft of the motor is fixedly connected with a bearing rod. The side wall of the bearing plate is fixedly connected with a servo motor, when the bearing plate encounters a protrusion on the inner wall of a pipeline, the protrusion extrudes a universal ball to enable a shell to move inwards, the shell drives a metal contact piece to make sliding contact with a sliding rheostat, resistance on the sliding rheostat is reduced, the sliding rheostat transmits current to an alarm lamp, and the alarm lamp is turned on. The alarm lamp can inform external personnel; the electromagnetic spring is powered on, the marking pen is pushed to make contact with the inner wall of the pipeline, the protrusions of the inner wall of the pipeline