A simple analogy to explain the transit time flow measurement principle is the example of a boat flowing in the river. A boat crossing a stream at an angle to the stream’s current will take less time to cross when going with the current than going against it. This time difference is proportional to the velocity of the stream’s current.
To relate this to a transit time flow meter, simply replace the boat with an acoustic signal. A upstream transducer (T1) sends a signal to a downstream transducer (T2) that in turn sends back a signal.
When there is no flow then time required to travel from T1 to T2 as well as time required from T2 to T1 remains the same.
However when there is a flow, the effect of flowing velocity on the acoustic signal is to assist the signal in the up to downstream direction & hinder the signal in the down to upstream direction.
This creates the time difference by which the liquid’s flowing velocity & ultimately the flow rate is determined. This meter can be used on clean liquid applications only like clean water, Chemicals, potable water, DM Water, petroleum products