Bidirectional; Polynomial - ABB 2600T Pressure Transmitter Series User Manual

364xS User's Manual

Bidirectional

The bidirectional function, applied to the transmitter
input (x) expressed in percentage of the calibrated
span, has the following form:
Output = ½ + ½ sign (x) I x I
where: x and Output should be normalized in the
range -1 to 1 for calculation purpose, with following
Output meaning: Output = 0 means Analog out 4 mA;
Output = 1 means Analog out 20 mA.
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.

Polynomial

The polynomial function, applied to the transmitter input (x) expressed in percentage of the calibrated span,
has the following form:
2
+ A x + A
Output = A x
0 1 2
where: x and Output should be normalized in the range 0 to 1 for calculation purpose, with following Output
meaning: Output = 0 means Analog out 4 mA; Output = 1 means Analog out 20 mA
This function can be used for linearization purpose: the user can plot the characteristic curve of the input and
find, using a mathematical method, the parameters of the polynomium that better approximate the plotted
curve. Check, after the calculation, if the maximum error is compatible with the application.
The following are some application examples.
Cylindrical vessel with flat ends
The following polynomium gives the area of the circular
section in relation to the heigth of the liquid in the vessel (h):
Output = - 0.02 + 0.297 h + 2.83 h
Volume = Output • (d/1.12838)
where: d = vessel diameter, L = vessel length.
Cylindrical vessel with hemispherical ends
The following polynomium gives the area of the circular
section in relation to the heigth of the liquid in the vessel (h):
Output = - 0.02 + 0.297 h + 2.83 h
Volume = Output • (d/1.12838)
where: d = vessel diameter, L = vessel length.
Cylindrical vessel with elliptical or pseudoelliptical ends
The following polynomium gives the area of the circular
section in relation to the heigth of the liquid in the vessel (h):
Output = - 0.02 + 0.297 h + 2.83 h
Volume = Output • (d/1.12838)
where: d = vessel diameter, L = vessel length, m = length of
the minor ellipse axis
1/2
3 4 5
+ A
+ A x + A x x
3 4 5
2 3
- 4.255 h + 3.5525 h
2
• L
2 3
- 4.255 h + 3.5525 h
2
• (L+ 2/3 d)
2 3
- 4.255 h + 3.5525 h
2
• (L+ 2/3 m)
Theoretical Square
Root Curve
-5 -4 -3 -2
Linear programmable
percentage value
4 5
-1.421 h
4 5
-1.421 h
4 5
-1.421 h
34
25
20 mA
20
15
10
5
12 mA
0
-1 0 1 2 3 4
-5
Cut off programmable
-10
percentage value
-15
4 mA
-20
-25
Configuration
5