Siemens SITRANS P500, Руководство по эксплуатации, Страница: 91 / 238

Operate
6.2 Parameter description
SITRANS P500 with HART
Operating Instructions, 12/2014, A5E02344528-09
91
Purpose: Activate bidirectional flow measurement
Description: The parameter enables the de/activation of a bidirectional flow measure-
ment.
Bidirectional flow measurement is applicable to whichever measurement
type is chosen, volume flow or mass flow.
In the case of a bidirectional flow measurement, the output flow is divided in
equal parts of forward measurements and backward measurements within
the range of 4 to 20 mA. The output current from 4 to 12 mA is used for
reverse measurement, the output current from 12 to 20 mA is used for for-
ward measurement. The type of characteristic selected using the flow char-
acteristic line parameter (lin, srlin, sroff, srlin2) applies equally to forward
and reverse flow.
If bidirectional flow measurement is selected, the following applies:
|MA| = |ME|
When bidirectional flow measurement is activated and the volume flow or
mass flow measurement type is selected, the start of scale values (MA
pres-
sure
, MA
volume flow
, MA
mass flow
) are set to the negative equivalents of the set-
tings for the full scale values (ME
pressure
, ME
volume flow
, ME
mass flow
).
The write access to MA
pressure
, MA
volume flow
, MA
mass flow
, is deactivated when
bidirectional flow measurement is activated.
Switching the measuring mode switch to a setting other than volume flow or
mass flow deactivates bidirectional flow measurement, if bidirectional flow
measurement was activated.
Deactivating the bidirectional flow measurement sets the values set for the
starts of scale value (MA
pressure
, MA
volume flow
, MA
mass flow
) to zero.
Deactivating the bidirectional flow measurement leaves the values set for
the full scale values unchanged.
"2.1.5.2 Transfer Function"
In this sub-menu you can select the characteristic that represents the relationship between
the input pressure and the output flow.
The root charactreistics differ from each other by their specific behaviour below the root
application point. The root application point can be freely selected between 1 % and 15 % of
the output value.
"2.1.5.3 Squareroot Startingpoint" (Page 92)
You can select from the following characteristic types of the output flow:
Factory setting: srlin2
Setting range:
• linear
•
srlin
• sroff
•
srlin2
Purpose: Selection of the pressure-flow characteristic