Proposed is a fluid metering device including a mixer receiving fluid in a storage tank, a metering tank metering and supplying the fluid to the mixer, a first transfer device transferring the fluid from the storage tank to the metering tank, a second transfer device transferring an input of the metered fluid to the mixer, a sensor measuring a fluid mass in the metering tank, and a controller stopping the first transfer device and activating the second transfer device with the initial remaining fluid greater than the input, and allowing the second transfer device to transfer the amount of input from the metering tank to the mixer, based on the fluid mass from the sensor and preset first and second metering set values, so that it is possible to quickly input a desired amount of fluid step by step, and to precisely adjust a fluid input into a final process.

The invention provides a fluid mixer with a fluid reservoir, a ring within the fluid reservoir, a stirrer rotatably coupled in the ring, and a motor to rotate the stirrer. The ring has a wall defining an inner and outer portion of the fluid reservoir, with wall cutouts that allow fluid to pass from the inner portion to the outer portion. The stirrer has a center and multiple paddles, and the rear surface of a first paddle and the front surface of a second paddle define a mixing space, and rotation of the paddles pushes a fluid from the mixing space through one of the cutouts into the outer portion. The invention also provides a method of mixing a fluid, including introducing liquid into a fluid reservoir and a powder into a powder dispenser, activating a stirrer, and dispensing the powder into the liquid while the stirrer is rotating.