ABB 2600T Series Instruction Manual page 57

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
Equations
Once the MV and PV are calculated and available in the PRTB then it can produces different type of measurements depending by
the selected PRTB_QUATERNARY_LIN_TYPE and applying the following formula:
Measurement Type QUATERNARY_LIN_TYPE
Pressure / Level
Flow
QLT
Volume QLT
Transfer Function
The transfer output functions available in the 266 Pressure Transducer Block are described in details
• Linear for differential, gauge and absolute pressure or level measurements
• Sq. Root (x) for flow measurements using restriction type primary element, like orifice plate, integral orifice, Venturi or Dall tube
and similar.
• 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.
• Bidirectional Flow
• Cylindrical lying tank
• Spherical tank
These output functions can be selected writing in PRTB_QUATERNARY_LIN_TYPE activated using a DD based Configuration Tool.
The transfer function can be applied to the Process Variable only or also to the indication (in engineering units).
Linear
Using this function, the relationship between the input (measured value), expressed in % of the calibrated span and the output is
linear (i.e.: at 0% input, corresponds 0% output - at 50% input corresponds 50% output - and at 100% input corresponds 100%
output). No further settings are possible here.
Square Root
Using the Square Root function, the output (in % of the span) is
proportional to the square root of the input signal in
percentage of the calibrated span (i.e.: the instrument gives an
analog output proportional to the rate of flow). The possibility
to have the full Square Root function is given.
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 when the signal is close to zero avoiding
errors due to the high gain of the square root.
Formula
Linear
PRIMARY_VALUE = CAL_VALUE [MV] +/- BIAS_VALUE
Linear
PV = CAL_VALUE [MV] +/- BIAS_VALUE
Square root
SV = (PV – PV_RANGE_0%) / (PV_RANGE_100% - PV_RANGE_0%)
SQRT 3° pow
QUATERNARY_VALUE [%] = (QLT (SV) * (QUATERNARY_100% -
SQRT 5° pow
QUATERNARY_0%) + QUATERNARY_0%
Bidirectional Flow
Cylindrical lying PV = CAL_VALUE [MV] +/- BIAS_VALUE
container
SV = (PV – PV_RANGE_0%) / (PV_RANGE_100% - PV_RANGE_0%)
QUATERNARY_VALUE [%] = (QLT (SV) * (QUATERNARY_100% -
Spherical container
QUATERNARY_0%)) + QUATERNARY_0%
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