Zero Point Adjustment - Siemens SITRANS F Operating Instructions Manual

Functions

8.2 Zero point adjustment

● Massflow: proportional to the phase difference between pickup 1 and pickup 2, with
● Volumeflow: derived directly from the ratio of massflow and media density.
● Corrected volumeflow: derived from the ratio of massflow and reference density
● Density: derived from the average frequency of sensor tube vibration with compensation
● Process media temperature: derived from the tube metal temperature. This is a legitimate
● Fraction A (massflow or volumeflow): derived from the combination of media density and
● Fraction B (massflow or volumeflow): ditto but fraction B is "Flow – A"
● Fraction A %: as for fraction A quantity but A% is the ratio between Fraction A flow and
● Fraction B %: ditto but B% is "100% – A%"
Metal temperatures are measured using precision Pt1000 sensors. The accuracy of the
1)
temperature measurement is ±1.0 °C.
Reference density is the density of the media at reference conditions, normally
2)
atmospheric pressure and 20 °C. Reference density can be programmed into the flowmeter
menu in two forms, either as a fixed reference or with a selection of linear or square-law
temperature dependence. The choice of fixed or calculated reference density and of linear or
square-law temperature dependency is according to the application and user preferences.
The customer-specified density/temperature tables may be derived from the mass fraction
3)
or volume fraction of any two-part mixture. Fraction calculations are naturally performed in
the ratio provided, or in mass ratio when using the built-in tables. Volume or mass ratios
derived from the fraction table are calculated through the composite media density.
8.2 Zero point adjustment
In the following the automatic zero point adjustment function is described. For further details,
see the appendix "Zero point adjustment" (Page 215).
NOTICE
Preconditions
Before a zero point adjustment is initiated, the pipe must be flushed, filled and at an
absolute flowrate of zero preferably also at operating pressure and temperature. Refer to
"Zero point adjustment" via LUI (Page 72) or PDM (Page 87) for more details.
112
compensations for changes in the metal characteristics due to tube and frame metal
temperatures .
1)
for changes in the metal characteristics with tube temperature. The relationship between
density and vibration frequency is an inverse square-law curve which can be fitted to 3
reference points being the densities of air, hot water and cold water.
measurement outcome since the tube walls are thin and they are within a sealed,
protected environment, thereby giving similar sensitivity as an insertion thermometer.
temperature, and compared with a stored table of fraction percentage against a wide
range of both process values through a fifth-order polynomial
Total flow
3)
SITRANS FC430 with HART
Operating Instructions, 03/2012, A5E03361511-01
.
2)