ABB 2600T Pressure Transmitter Series User Manual page 33

364xS User's Manual
To avoid the extremely high gain error with the input
approaching zero, the transmitter output is linear with
the input up with a slope of 1 up to 0.5% and then still
linear with the appropriated slope to a programmable
percentage value between 10 % and 20%. This option
is offer in order to ensure a more stable output near
zero. This also allows an easier zero adjustment and
performs a reduced zero error for ambient temperature
variations.
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.
3
The x 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,
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 mesured
by the transmitter) is proportional to h
3
of h . 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.
5
The x Square root Transfer function can be used for
open channel flow measurement using ISO 1438 V-
notch (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 h
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).
Rehbock
3/2
or square root
5/2 5
or square root of h .
25
20
Theoretical Square
Root Curve
15
10
5
0
0 1 2 3
%
Slope = 1
25
20
Theoretical Square
Root Curve
15
10
5
programmable
percentage value
0
0 1 2 3
%
33
programmable
percentage value
4 5 6
4 5 6
Configuration