Endress+Hauser Proline Prowirl 73 - Page 144

Description of device functions Proline Prowirl 73
144 Endress+Hauser
SELECT FLUID
(contd.)
Selected fluid: GAS VOLUME or LIQUID VOLUME
Applications:
The measured volume flow and measured temperature are made available to an external
flow computer (e.g. RMC621). In conjunction with an
external pressure transmitter (PT), the flow can be calculated at a non-constant pressure.
Calculated variables:
No variables are calculated in the measuring device. Any calculations are made in the
flow computer.
Sample application:
A0001983
Selected fluid: SUPERHEATED STEAM
Applications:
For calculating the mass flow and the quantity of heat the flow contains.
!
Note!
The process pressure (p) in the process pipe is required to calculate the process variables
and the measuring range limit values. The process pressure can be read in from an
external pressure measuring device (e.g. Cerabar-M, for details on wiring ä 27) via
the HART INPUT (ä 167), or can be entered as a fixed value in the OPERATING
PRESSURE function (ä 150).
The following aspects are taken into account when calculating the values:
• The device will calculate assuming superheated steam until the saturation point is
reached. Notice message "#525 WET STEAM ALARM" ä 68 is triggered at 2 °C
above saturation. This alarm can be switched off via the WET STEAM ALARM
function (ä 156).
• If the temperature is lowered even further, the meter will calculate assuming saturated
steam based on temperature down to 0 °C. If pressure is preferred as the measured
variable, it can be selected in the SATURATED STEAM PARAMETER function
(ä 157).
• Below 0 °C the meter will continue calculating assuming saturated steam of 0 °C.
Calculated variables:
The mass flow, heat flow, density and the specific enthalpy are calculated from the
measured volume flow and measured temperature using the saturated steam curve as per
the international IAPWS-IF97 standard (ASME steam data).
Formulae for calculation:
• Mass flow: m = q ·  (T, p)
• Quantity of heat: E = q ·  (T, p) · h
D
(T, p)
m = Mass flow
E = Quantity of heat
q = Volume flow (measured)
h
D
= Specific enthalpy
T = Operating temperature (measured)
p = Process pressure (ä 150)
 = Density*
* from steam data as per IAPWS-IF97 (ASME), for the measured temperature and the
specified pressure
(Continued on next page)
Function description, FLOW COMPUTER group
PT
RMC 621