ABB 264B, Руководство по эксплуатации

Страница: 6 / 56

With secondary electronics HART, it is to be consider
that different communication protocols exist for configuration
and maintenance operations. Here follows a brief description
on the matter; please refer to appropriate technical specification
for additional deeper explanations on the communication
aspects.
The HART protocol is based on the standard Bell 202 FSK
(Frequency Shift Keying ) with a
±
0.5 mA signal modulation
superimposed on the 4 to 20 mA analog signal. As the energy
balance added to the current loop is virtually zero and the
frequency is very high compared to that of the process dynamic,
the analog process signal remains undisturbed.
. . . PRINCIPLE OF OPERATION
Internal Serial Bus
Parallel Bus
SENSOR
INTERFACE
DIGITAL
CONVERTER
123456789012345678
123456789012345678
123456789012345678
123456789012345678
123456789012345678
MICRO
CONTROLLER
EXT. ADJ
INTERFACE
MEMORY
4 to 20 mA
CONVERSION
MEMORY
Primary electronics
(located in the
Primary Unit)
Sensors
Internal bus
Fig. 3 - Functional Block Diagram
MODEM FSK
COUPLER
Zero
Span
Secondary Electronics
(located in the
Secondary Unit)
4 to 20 mA
Output
The microprocessor receives data from the internal modem, in order to provide bidirectional digital communication with the
configuration device, i.e. the Hand Held terminal "Communicator" or P.C. based "Configurator".
Using a configuration device it is then possible to remotely
modify the configuration of the transmitter, e.g. the measuring
range.
It is also possible to read other transmitter data and diagnostic
information. Limited rezeroing and respanning, comparable to
that conventional analog transmitters is possible using the
optional calibration device. Refer to Fig. 3 for a complete view
of the Functional Block Diagram.
The sensor and all electronic parts are galvanically isolated
from the transmitter body.
- 6 -
External Zero/Span
adjustments
Fig. 2d - Secondary Unit
Output meter
(option)
Surge protector
(option)
Terminal
block
Housing Electronics
Integral meter
(option)
RFI filter