CiDRA SONARtrac PW VF-100 - Manual (Page 150)

20834-01 Rev 04 Page 8-6
For applications where the process pressure varies, it is
recommended that a correction for pressure be performed in the
process control system. Alternatively, a pressure transmitter can be
input to the passive sonar meter transmitter as described in Pressure
Sel below.
If a plant control system is used to correct for pressure, the correction
at the control system is made as follows:
GVF
act
= GVF
meas
* [(P
proc
+ P
atm
)/ (Ptrans + P
atm
)]
Where: GVF
act
= the GVF corrected for pressure
GVF
meas
= the GVF reported by the transmitter
P
atm
= 14.696 if at sea level, correct for elevation if necessary (psia)
P
proc
= the pressure from the pressure transducer (psig)
P
trans
= the pressure input to the transmitter (psig)
If a pressure transmitter is connected to the passive sonar meter
transmitter, the calculation above is performed by the transmitter unit
and no pressure correction should be made in the process control
system.
8.2.6 Temperature (Systems with GVF)
The Temperature input is used to input the approximate or average
process / fluid temperature (in ºC or ºF). A temperature transmitter
can be input to the passive sonar meter transmitter as described in
Temperature Sel below.
This input has minimal affect on GVF calculation. Therefore, an
approximate process temperature value is usually sufficient.
8.2.7 Pressure Sel (Systems with GVF)
Pressure Sel is used to select if the pressure values for calculating
GVF will be fixed (that is, assumed to be steady state and use the
values input earlier during GVF set up), or if the values will be based
on a pressure transducer. If the values are based on a pressure
transducer
, user must configure the sensor inputs in the ‘Input
Config ’ menu.
8.2.8 Temperature Sel (Systems with GVF)
Temperature Sel is used to select if the temperature values for
calculating GVF will be fixed (that is, assumed to be steady state and
use the values input earlier during GVF set up), or if the values will be
based on a temperature transducer. If the values are based on a
temperature transducer, user must configure the sensor inputs in the
‘Input Config’ menu.