Introduction
V
Introduction
The LD302 is of the 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,
an easy interface between the field and the control room and several interesting features
that 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 multi-dropping of several devices on a single pair of wires.
Those protocols were not intended to transfer control data, but maintenance information.
Therefore they were slow and not efficient enough to be used.
The main requirements for Fieldbus were 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 was 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, not loosing 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 too 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 is 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 Function Blocks built in, like PID
controller, Input Selector and Splitter/Output Selector, eliminating the need for separate
control device. This feature reduces communication and by that 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 on its own, but also replaces the circuit board for the
LD301. They 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.
