Square Root To The 3Rd Power; Square Root To The 5Th Power; Custom Linearization Curve - ABB 266 HART Operating Instruction

266 Models - HART
Figure 46: Square-Root transfer functions

Square root to the 3rd power

The x3 Square root Transfer function can be used for open channel (see figures on the right) flow measurement using ISO 1438
rectangular weirs (Hamilton Smith, Kindsvater-Carter, Rehbock formulas) or trapezoidal weirs (Cippoletti formulas) and ISO 1438
Venturi flumes. In these types of devices the relationship between the flow and the developed head h (the differential pressure
measured by the transmitter) is proportional to h3/2 or square root of h3. Other types of Venturi or Parshall flume do not follow this
relationship.
Using this function, the output (in % of the span) is proportional to the square root of the third power of the input signal in % of the
calibrated span: the instrument gives an output proportional to the rate of flow calculated using the above mentioned formulas.
Figure 47: Tanks (respectively rectangula weir, trapezoidal weir and V-notch weir)

Square root to the 5th power

The x5 Square root Transfer function can be used for open channel flow measurement using ISO 1438 Vnotch (triangular) weirs
(see figure on the right) where the relationship between the flow and the developed head h (the differential pressure measured by
the transmitter) is proportional to h5/2 or square root of h5.
Using this function, the output (in % of the span) is proportional to the square root of the fifth power of the input signal in % of the
calibrated span: the instrument (it gives an output proportional to the rate of flow calculated using the Kingsvater-Shen formula).

Custom linearization curve

The custom linearization curve transfer function it is used typically for volumetric level measurement in tanks with an irregular
shape. It can be registered to a freely identifiable transfer function with a maximum of 22 base points. The first point is always the
zero point, the last is always the final value. Neither of these points can be altered.
A maximum of 20 points can be freely entered in between.
These points have to be defined by extrapolating the tank filling table data and reducing them to 22 points.Once identified the 22
points they will need to be uploaded into the device by either using an HART hand held terminal or a proper configuration soft-
ware like Asset Vision Basic.
56 OI/266/HART-EN Rev. D | 2600T Series Pressure transmitters