)
, an open communication protocol for addressable remote sensor high-speed channels, is a communication protocol launched by an American company in
for use between on-site smart instruments and control room equipment. .
The device provides communication with relatively low bandwidth and moderate response time. After
years of development,
the technology has become very mature abroad and has become the industry standard for global smart meters.
The protocol uses a frequency shift keying signal based on the
standard, superimposing an audio digital signal with an amplitude of
on the low-frequency
analog signal for two-way digital communication
/> message, data transfer rate
. Since the average value of the
signal is
, it does not affect the size of the analog signal transmitted to the control system, ensuring compatibility with existing analog systems. In
protocol communication
the main variables and control information are transmitted by
and, if necessary, additional measurement, process parameters, device configuration, calibration, diagnostic information via
Protocol access.
The communication adopts a half-duplex communication method, which is characterized by realizing digital signal communication on the existing analog signal transmission line. It is a transitional product in the process of transforming from analog system to digital system, so it is currently
During the transitional period, it had strong market competitiveness and achieved rapid development.
It specifies a series of commands and works according to the command mode. It has three types of commands. The first type is called general commands, which are understood and executed by all devices. The second type is called general behavior commands. The functions provided can be used on many field devices (although not all ), this type of commands includes the most commonly used field device function libraries. The third category is called special device commands, which are used to facilitate the implementation of special functions in certain devices. This type of commands can be used in the foundation. It is open for use in China and can be exclusive to the company that developed the command. It is common to find a combination of these three types of commands in a field device.
Use a unified device description language
. Field device developers use this standard language to describe device characteristics. The
foundation is responsible for registering and managing these device descriptions and compiling them into device
description dictionaries. The main device uses
technology to understand Characteristic parameters of these devices without having to develop dedicated interfaces for these devices. However, due to this analog-digital mixed-signal system, it is difficult to develop a communication interface chip that can meet the requirements of various companies.
It can use bus power supply, which can meet the intrinsic safety and explosion-proof requirements, and can form a dual-master equipment system with a handheld programmer and a management system host as the main equipment.
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