Medium Density in kg/m³ UnitSI Unit m

K K1or1

2 kg/dm³1 kg/dm³= 1,000 kg/m³ g/cm³1 g/cm³ = 1,000 kg/m³ kg/l1 kg/l = 1,000 kg/m³ In contrast to many other primary elements, thedeltaflow’s resistance coefficient in turbulent flow is not dependent on the flow itself or on the medium (Reynolds).If for some reason you do not receive a calculationsheet with your deltaflow, you can order one from systec Controls by providing the serial number from your unit. Or you can use the free deltacalc software, which can be downloaded from the systec Controls website at

General Basic Calculation Information

The way flow is calculated with the deltaflow is similarto the way flow is calculated according to EN ISO 5167-1 (formerly DIN 1952). The following formula applies to flow: www.systec-controls.de.
2

241 dpdq

Bm (1)

Expansion Number

Formula Symbol Measurement SI Unit The expansion number (Epsilon) defines the effect ofthe pressure loss and the resulting change in the density of the medium on the flow measurement.In the case of incompressible media (liquids), pressureloss at the primary element does not result in anychange in density, so the expansion number is 1.In the case of compressible media (gasses, steam), theexpansion number varies proportionally from 1 as the amount of pressure loss at the primary element increases and as the static pressure within the conduit decreases.Because the deltaflow causes only a very minorpressure loss, the expansion number is usually very close to 1. You will find the expansion number at thedesign point

q

m Mass flowkg/s Probe-specific resistancecoefficient (blockagefactor)- Expansion Number(for incompressible media=1)- dConduit interior diameterm dpDifferential pressurePa
3 B Medium density underoperating conditionskg/m Index Meaning NStandard conditions(101,325 Pa, 273.15K) BOperating conditions (current pressureand current temperature inside theconduit)
D listed on your deltaflow calculationsheet.When calculating flow, the expansion number is oftenassumed to be a constant. To do this, the expansion number is generally calculated as 2/3 of the maximum flow qmax ( DDesign conditions (pressureand temperature settings incorporatedinto the deltaflow design, identified onthe calculation sheet)
3/2 ). For deltaflow purposes it is veryeasy to calculate
3/2 from
D :

Resistance Coefficient

3/2 D

)1(941

You will find the resistance coefficient (Zeta) onyour deltaflow calculation sheet. In some documentsthe probe factor K ( K number ) is used instead of For applications in which the expansion number variessignificantly from 1, calculating the actual current expansion number can increase the accuracy of the quantity measurement. The actual current expansion number .There is a simple correspondence between and the Knumber, and conversion between the two is easy:
B can be calculated from the designexpansion number
D as follows: deltaflow Basic Calculation Information 07/03Page3