... pressure loss 4, Easy installation Electronic flow sensor (Thermal differential type)Principle Based on the principle of thermal theory, there are two resistances ... be changed . The differential resistances value is the basis of determining the flow velocity . Feature1,No movable parts . 2, Maintenance free. ... …150cm/s( water),3…300cm/s(oil),20…2000cm/s(air)Output: PNP, NPN, Relay ,4-20mA, NO+NC (SPDT) ...