ABB 2600T Series Instruction Manual page 56

56 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
Pressure Transducer Block (PRTB)
Overview
This pressure transducer block is implemented within devices whose primary process sensor has the purpose to measure pressure,
or differential pressure (P-dP)
In addition, at the pressure value as primary measurement, there are other variables that can be selected trough the Channel as
input for the Analog Input blocks, these are the Sensor Temperature, the Static Pressure, for Differential pressure sensors only, and
the Scaled PV identified respectively as Secondary, Tertiary and Quaternary variables
Block Diagram
Description
The Physical I/O represents the physical interface with the process and is part of the device's Pressure Transducer.
The physical I/O takes care to execute the basic manufacturer device specific algorithm with the purpose to convert the raw signal
representing the measured process value into a digital format. The physical I/O operations are:
1 Sampling of the primary raw signal changing according the process changes.
2 Validation and Elaboration of the sampled primary raw signal
3 Linearization and Compensation
Result of the above operations is the RAW_VALUES produced in output of the physical I/O, see the Block Diagram, and used as
input for the Pressure Transducer Block.
The first Pressure Transducer Block operation is the Calibration/trimming of the RAW_VALUES in order to adjust its digital value to
match the real pressure measured by the Sensor block.
The RAW_VALUES after the calibration became the calibrated Measured Values (MV) represented by the PRTB_CAL_VALUE and, for
differential sensors only, PRTB_STATIC_P_TRIM_VALUE.
These Measured Values matches and represents the real inputs sampled by the sensor and any further calculation has the scope to
transform them to a Process Variables (PV).
In this perspective the first calculation applied is the elevation/suppression within the PV-Bias/Offset step executed for different
reasons like the correction of the mounting position or for example in any condition where part of the measure must not be
considered as part of the process.