ABB 266 Operating Instruction page 10

266 Models - FOUNDATION Fieldbus
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 Linear
Linear
Square root
Flow QLT
SQRT 3° pow
SQRT 5° pow
Bidirectional Flow
cylindrical lying container
Volume QLT
spherical container
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
– Custom linearization table
– 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. 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.
10 OI/266/FF/ADD-EN Rev. B | 2600T Series Pressure transmitters
Formula
PRIMARY_VALUE = CAL_VALUE [MV] +/- BIAS_VALUE
PV = CAL_VALUE [MV] +/- BIAS_VALUE
SV = (PV – PV_RANGE_0%) / (PV_RANGE_100% - PV_RANGE_0%)
QUATERNARY_VALUE [%] = (QLT (SV) * (QUATERNARY_100% - QUATERNARY_0%) +
QUATERNARY_0%
PV = CAL_VALUE [MV] +/- BIAS_VALUE
SV = (PV – PV_RANGE_0%) / (PV_RANGE_100% - PV_RANGE_0%)
QUATERNARY_VALUE [%] = (QLT (SV) * (QUATERNARY_100% - QUATERNARY_0%)) +
QUATERNARY_0%
Figure 45: Linear output