SMAR ld301 - Transfer Function for Flow Measurement

Configuration
3.9
The user unit may be selected from a list of options included in the LD301. Table 3.2 makes it possible
to associate the new measurement to the new unit so that all supervisory systems fitted the HART

protocol can access the special unit included in this table. The user will be responsible for the
consistency of such information. The LD301 does not verify if the values corresponding to the 0% and
100% inserted by the user are compatible with the selected unit.
VARIABLE UNITS
Pressure
inH
2
O, inHg, ftH
2
O, mmH
2
O, mmHg, psi, bar, mbar, gf/cm
2
, kgf/cm
2
, Pascal,
Torriceli, atm, Mpa, inH
2
O @ 4
o
C, mmH
2
O @ 4
o
C, mH
2
O, mH
2
O @ 4
o
C.
Volumetric Flow
ft
3
/m, gal/mim, min, Gal/m, m
3
/h, gal/s, I/s, MI/d, ft
3
/d, m
3
/s, m/d, Ga/h, Ga/d, ft
3
/
h, m
3
/min, bbl/s, bbl/min, bbl/d, gal/s, I/h, gal/d.
Velocity
ft/s, m/s, m/h.
Volume
gal, litro, Gal, m
3
, bbl, bush, Yd
3
, Pé
3
, In
3
, hl.
Level
ft, m, in, cm, mm.
Mass
grama, kg, Ton, lb, Sh ton, Lton.
Mass Flow
g/s, g/min, g/h, kg/s, kg/m, kg/h, kg/d, Ton/m, Ton/h, Ton/d, lb/s, lb/m, lb/h, lb/d
Density
SGU, g/m
3
, kg/m
3
, g/ml, kg/l, Twad, Brix, Baum L, API, % Solw, % Solv, Ball.
Others
CSo, cPo, mA, %.
special
5 caracteres. (See HART® Special Units in section 5).
Table 3.2 – Available User Units
Should a special unit other than those presented on Table 3.2 be required, the LD301 allows the user to
create a new unit by entering up to 5 alphanumeric digits. The LD301 includes an internal feature to
enable and disable the User Unit.
Example: transmitter LD301 is connected to a horizontal cylindrical tank (6 meters long and 2 meters in
diameter), linearized for volume measurement using camber table data in its linearization table.
Measurement is done at the high-pressure tap and the transmitter is located 250 mm below the support
base. The fluid to be measured is water at 20 C. Tank volume is: [(.d2)/4].l = [(.22)/4].6 = 18.85 m3.
The wet tap shall be subtracted from the measured pressure in order to obtain the tank level. Therefore,
a calibration without reference shall be carried out, as follows:
In Calibration:
Lower = 250 mmH
2
O
Upper = 2250 mmH
2
O
Pressure unit = mmH
2
O
In User Unit:
User Unit 0% = 0
User Unit 100% = 18.85 m³
User Unit = m
3
When activating the User's Unit, LD301 it will start to indicate the new measurement.
Transfer Function for Flow Measurement
The function can be used to linearize the measured pressure to flow or volume. The following functions
are available:
NOTE
 Use the lowest required damping to prevent measurement delays;
 If the square root extraction for flow measurement is carried out externally by other loop element, do
not enable this function on the transmitter
SQRT - Square Root. Considering the pressure input X varying between 0 and 100%, the output will
be
x10 . This function is used in flow measurement with, e.g., orifice or Venturi tube etc.
The Square Root has an adjustable cutoff point. Below this point the output is linear, if the cutoff mode is
bumpless with the differential pressure as indicated by the Figure 3.5. If the cutoff mode is hard the
output will be 0% below the cutoff point. The default value for Cutoff is 6% of ranged pressure input. The
maximum value for cutoff is 100%. Cutoff is used to limit the high gain, which results from square root
extraction on small values. This gives a more stable reading at low flows.