Basics of dp-operation Welcome to systec Controls Principles of dp-Operation

Principles of dp-measurement Principles of dp- Measurement How do dp-Mesurements work? Equations of the EN-ISO 5167 Types of standard dp elements Acvantages and disadvantages of various dp-elemets calculation of dp-elements

Principles of dp-measurement Energieerhaltungsprinzip cinetic + potential Energy is constant Dp-measurement means conversion of potential Energy (pressure) into cinetic energy (velocity)

Principles of dp-measurement Principle of constant Energy Orifice: In the neck, velocity increases (cinetic E increases) and pressure decreases (potential E decreases)

Principles of dp-measurement Integrating pitot tube: At the impact point of the probe, the velocity is zero (cinetic E decreases) an the pressure raises (potential E increases) Principle of constant Energy

Principles of dp-measurement Flow Equation of EN ISO Flow Equation of deltaflow

Principles of dp-measurement Flow equation CFlow factor, depending on dimensions and Reynolds ßDiameter ratio d/D  blockage factor  expansion factor (takes densitiy variations in account) dpdifferential pressure  denistiy at working conditions

Principles of dp-measurement Flow equation for liquids When measuring liquids, the equation is less complicated:  =1 , C and  are almost constant ß, d and  are constant

Principles of dp-measurement The term is similar to the deltaflow term These are factors, which have been developed by experiments The blockage factor  is from Re=8000 constant C is a function of Reynolds (Re) and does depend on flow exampel: orifice; DN 200; ß=0,5 Re= , C=0,6056 Re= , C=0,6032 Error in C= 0,4% deltaflow, DN200 Re= ,  =2,4093 Re= ,  =2,4093 Error in  =0,0% For big flow spans, the Re-impact on C must be compensated! The effect of C and 

Principles of dp-measurement Due to the pressure loss at the primary element, density of compressible fluids change. Thais has an influence on the flowmeasurement which is compensated by . For incompressible fluids:  =1 Exampel: Air, 20°C, 1bar Orifice; DN200; ß=0,6deltaflow 200 Nm³/h  =0,9999  =1, Nm³/h  =0,9844  =0,9984 Änderung 1,55%0,16% The effect of  For big flow spans, the impact of  must be compensated!

Principles of dp-measurement Pressure loss of primary devices (see VDI/VDE ) High pressure steam example ID 250, 185bar, 540°C, 550 t/h deltaflowVenturi-nozzleorifice beta0,740,8 dp2011 mbar1998 mbar3367 mbar Pressure loss169 mbar299 mbar1111 mbar cost (6Pf/kWh) DM/a DM/a DM/a

Principles of dp-measurement Uncertaincies of primary devices (see VDI/VDE 2040) Uncertaincies of standard primary devices: 0,6-2% Uncertaincies of deltaflow: <0,6%

Principles of dp-measurement Mechanical construction Orifice Venturi Nozzels

Principles of dp-measurement Advantages and disadvatages