Introduction
III
Introduction
The LD302 is part of first generation of Fieldbus devices. It is a transmitter for differential, absolute
and gauge pressure, level and flow measurements. It is based on a field-proven capacitive sensor
that provides reliable operation and high performance. The digital technology used in the LD302
enables the choice of several types of transfer functions, and easy interface between the field and
the control room. Also it has several interesting features that will considerably reduce the
installation, operation and maintenance costs.
The LD302 is part of Smar's complete 302 line of Fieldbus devices.
Fieldbus is not only a replacement for 4-20 mA or intelligent / smart transmitter protocols, it contains
much more. Fieldbus is a complete system enabling distribution of the control function to equipment
in the field.
Some of the advantages of bi-directional digital communications are known from existing smart
transmitter protocols: Higher accuracy, multi-variable access, remote configuration and diagnostics,
and the multi-dropping of several devices on a single pair of wires.
These protocols are not intended to transfer control data, but maintenance information. Therefore
they are slow and too inefficient to be used.
The main requirements for Fieldbus are to overcome these problems. Closed loop control with
performance like a 4-20 mA system requires higher speed. Since higher speed means higher power
consumption, this clashes with the need for intrinsic safety.
Therefore, a moderately high communication speed has been selected, and the system was
designed to have a minimum of communication overhead. Using scheduling, the system controls
variable sampling, algorithm execution, and communication so as to optimize the usage of the
network, will not lose time. Thus, high closed loop performance is achieved.
Using Fieldbus technology, with its capability to interconnect several devices, very large control
schemes can be constructed. In order to be user friendly, the function block concept was introduced
(users of SMAR CD600 should be familiar with this, since it was implemented several years ago).
The user may now easily build and overview complex control strategies. Another advantage was
added: flexibility. The control strategy may be edited without having to rewire or change any
hardware.
The LD302, like the rest of the 302 family, has several built-in Function Blocks, such as the PID
controller, Input Selector and Splitter/Output Selector, therefore eliminating the need for a separate
control device. This feature reduces communication, so there is less dead-time and tighter control,
not to mention the reduction in cost.
Other function blocks are also available. They allow flexibility in control strategy implementation.
The need for implementation of Fieldbus in small as well as large systems was considered when
developing the entire 302 line of Fieldbus devices. They have the common features of being able to
act as a master on the network and be configured locally using a magnetic tool, eliminating the need
for a configurator or console in many basic applications.
The LD302 is available as a product of its own, but also replaces the circuit board for the LD301.
They both use the same sensor board. Refer to the maintenance section of this manual for
instructions on upgrading. The LD302 is part of SMAR's Series 302 of Fieldbus devices.
The LD302, like its predecessor LD301, has many built-in blocks, eliminating the need for a
separate control device. The communication requirement is considerably reduced, and that means
less dead-time and tighter control is achieved, not to mention the reduction in cost. They allow
flexibility in control strategy implementation.
Get the best results of the LD302 by carefully reading these instructions.
