Transfer Functions Description; Linear; Polynomial - ABB 364G Series Manual

Linear

for differential, gauge and absolute
pressure or level measurements
Sq. Root (x3)
for open channel flow measurements
using rectangular or trapezoidal weir
Sq. Root (x5) for open channel flow measurements
using V-notch (triangular) weir.

Polynomial

for input linearization using a 5th-order
polynomial function for input
linearization using 2 polynomial
functions of 2nd order
Costant current for loop or associated equipment test.
These output functions can be activated using a Configuration Tool (CoMeter, Digital LCD Integral Display,
Hand Held Communicator and PC).
The transfer function can be applied to the analog signal 4 to 20 mA or to the indication (in engineering units)
on the CoMeter with the 695 Field Indicator and/or to the Digital LCD Integral Display.

Transfer functions description

Linear
Using this function, the relationship between the i nput (measured value), expressed in % o f the cali brated
span and the output i s linear (i.e.: at 0 % input, corresp onds 0% output - 4mA - at 5 0% input corresponds
50% output - 12mA - and at 100% input corresponds 100% output - 20mA).
Polynomial
The polynomial function, applied to the transmitter input (x) expressed in percentage of the calibrated span,
has the following form:
Output = A + A x + A
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, th e parameters of the polyn omium that b etter approximate the pl otted
curve. Check, after the calculation, if the maximum error is compatible with the application.
2 3 4
x + A x + A x + A x
3 4 5
Note: x and output are in the range 0 to 1 (0% to 100%)
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364Ax-Gx Instruction Manual
Pressure
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