Complex sentence: A disadvantage of using a DP flowmeters is that they introduce a pressure drop into the flowmeter line, this is a necessary result of the constriction in the line that is required to make the DP flow measurement.
Split into simpler sentences: A disadvantage of using a DP flowmeters is that they introduce a pressure drop into the flowmeter line. This is a necessary result of the constriction in the line that is required to make the DP flow measurement.