Principle Of Operation - ABB 2600T Series Operating Instruction

PRINCIPLE OF OPERATION

The instrument consists of two functional units:
- Primary Unit
- Secondary Unit
The Primary Unit includes the process interface and the
sensor, the Secondary Unit includes the electronics, the terminal
block and the housing. The two units are mechanically coupled
by a threaded joint. All units are based on custom integrated
components (Application Specific Integrated Circuit - ASIC).
The principle of operation of the Primary Unit is as follows. The
process fluid ( liquid, gas or vapour ) exerts pressure on to the
measuring diaphragm via flexible, corrosion-resistant isolating
diaphragm and the fill fluid (see Fig. 2a). The other side of the
measuring diaphragm is either at "atmosphere", for gauge
measurement, or at "vacuum", for absolute measurement. As
the measuring diaphragm deflects in response to input pressure
changes, it simultaneously produces variations in the gap
between the magnetic disc and the magnetic core of the coil,
which is mounted rigidly on to the primary body. As a result, the
inductance of the coil changes.
The inductance values of the coil is compared to that of a
reference inductor carried by the primary electronics.
Output meter
Input
Fig. 2a - Primary Unit
(option)
Surge protector
(option)
Terminal
block
Housing
Fig. 2b - Secondary Unit
Primary Electronics
Printed Circuit
Inductance Coil
& Magnetic Core
Ferrite disc
Sensor Diaphragm
Reference chamber
Isolating Diaphragm
Process
connection
The unit also includes a temperature sensor. The two inductance
values and the sensor temperature, are combined in the
primary electronics to provide a proprietary standard signal.
Consequently the further elaboration, together with temperature
signal is equivalent allowing to use the same secondary
electronics.
In the manufacturing process the sensor output characteristics
are compared with reference pressures and temperatures: the
"mapped" parameters are then stored in EEPROM # 1.
The measured values and the sensor parameters are transferred
to the Secondary Unit, where a microprocessor computes
precise primary output linearisation, compensating for the
combined effects of sensor non linearity and temperature
changes. In the secondary electronics EEPROM #2 stores
specific transmitter information:
- non modifiable data such as the serial number, the UID
(Unique Identifier), the manufacturer's name and device type,
the hardware and software version of the electronics.
- the modifiable data such as the final trimming and calibration
ie., all data that can be changed by the user through the
configurator devices.
External Zero/Span
adjustments
RFI filter
Electronics
- 9 -