Principle does not rely on the salt in the water, you are worried about should be electromagnetic flow meter. Electromagnetic flow meter is a kind of inductive meter according to Faraday's law of electromagnetic induction to measure the volume flow of conductive media in the pipe, so there is a relationship with the salt.

Ultrasonic flowmeter is through the detection of fluid flow on the ultrasonic beam (or ultrasonic pulse) in order to measure the flow rate of the meter.

Principle: According to the principle of signal detection ultrasonic flowmeter can be divided into propagation velocity difference method (direct time difference method, time difference method, phase difference method and frequency difference method), beam shift method, Doppler method, mutual correlation method, spatial filtering method and noise method.

Advantages: (1) non-contact measurement; (2) no flow obstruction measurement, no pressure loss; (3) measurement of non-conductive liquids, no obstruction measurement of electromagnetic flowmeter is a complement.