ABB 2600T Series Instruction Manual page 58

58 2 6 0 0 T S E R I E S | P R E S S U R E T R A N S M I T T E R S | O I/ 2 6 6/ F F - E N R E V. E
To neglect the values with the input approaching zero, the transmitter output is zero with the input up to a programmable
percentage value between 0 % and 20%. This option is offer in order to ensure a more stable flow measure.
This option is possible for all the listed output functions.
Square root to the 3rd power
The 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.
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).
Bidirectional Flow
This mode is used when the transmitter is connected to a bidirectional flow element (wedge meter etc). The bidirectional function,
applied to the transmitter input (x) expressed in percentage of the calibrated span, has the following form:
Output = 1/2 + 1/2 sign (x) · x 1/2 where: x and Output should be normalized in the range 0 to 1 for calculation purpose, with the
following Output meaning:
• Output = 0 means 0%
• Output = 1 means 100%
This function can be used for flow measurement purpose when the flow is in both the directions and the primary elements are
designed to perform this type of measure. As an example, if we have a bidirectional flow measurement application with the
following data:
• Max reverse flow rate: -100 lt/h
• Max flow rate: +100 lt/h