Principle Of Operation - ABB Industrial IT enabled 2600T Series Operating Instruction

PRINCIPLE OF OPERATION

MODELS: 262/264 D-V-P
Resin potting
Inductance Coils
& Magnetic
Cores
Capillary tubing
Isolating
diaphragm
Process
chamber
Fig. 2a - Primary Unit
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. The Electronics of Secondary Unit is based
on custom integrated
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
sensor diaphragm via flexible, corrosion-resistant isolating
diaphragms and capillary tubing containing the fill fluid (see
Fig. 2a). This is for inductive principle.
As the sensor diaphragm deflects in response to differential
pressure changes, it simultaneously produces variations in the
gap between two fixed magnetic circuits (comprising coil and
ferrite core) positioned on both sides of the measuring
diaphragm. As a result, the inductance of each coil changes.
The two inductance values L1 and L2, and the sensor
temperature ST are combined in the primary electronics to
provide a proprietary standardized signal.
In the manufacturing process the sensor output characteristics
are compared with reference pressures and temperatures: the
"mapped" parameters are then stored in the memory of Primary
electronics.
Primary Electronics
Printed Circuit
Sensor Diaphragm
with Ferrite Disks
Capillary tubing
Isolating
diaphragm
Process
chamber
components (Application Specific
While maintaining the modular construction, it may be adopted
a sensor module different then the inductive one. The sensor
can be piezoresistive. The completely welded sensor module
is a twin-chamber system with an integral overload diaphragm,
an internal absolute pressure sensor and a silicon differential
pressure sensor.
The absolute pressure sensor, which is only exposed to the
pressure at the high pressure side, acts as a reference value
to compensate for the static pressure.
The differential pressure sensor is connected via a capillary
tube to the negative side / the reference vacuum of the sensor
module. The applied differential pressure (dp) / absolute
pressure (pabs) is transferred via the separating diaphragm
and the fill fluid to the diaphragms of the silicon differential
pressure sensor.
A minimal deflection of the silicon diaphragm changes the
output voltage of the pick-up system. This output voltage,
proportional to the pressure, is converted by the matching unit
and the amplifier into an electrical signal.
Depending on the model, the transmitter is connected to the
process by means of oval flanges with fixing threads according
to DIN 19213 (M10/M12) or 7/16 - 20 UNF, 1/4 - 18 NPT Female
thread or remote seal.
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, of static pressure and
temperature changes. In the secondary electronics permanent
memory are stored the transmitter specific 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,
in other words, all data that can be changed by the user
through the configuration devices.
MODELS 262/264 B
Microprocessor-based
Isolating diaphragm
dp - sensor
Pabs - sensor
Filling liquid
Process connection
Overload diaphragm
Sensor body
Fig. 2b - Piezoresistive sensor
for differential pressure
electronics
Matching
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