BENTLY 3500/05-01-02-00-00-00 3500 System Rack

BENTLY 3500/05-01-02-00-00-00 3500 System Rack

Introduction
PLC is often used for interlocking and control of large units in petrochemical production. For the vibration, displacement and other parameters of the unit, when the number of points is small, transmitters and sensors can be used to convert them into 4-20mA signals and send them to the PLC to achieve interlocking control. However, for special measurement parameters such as key phase and differential expansion, or when there are many measurement parameters such as vibration and displacement, the difficulty and cost of signal conversion are high. Using traditional frame type mechanical protection systems will be more economical and effective. The Bently 3500 system from the United States is one of the traditional framework based mechanical protection systems that can operate at various levels of redundancy, including dual power supply and triple module redundancy (TMR) monitor configurations with higher requirements. Each I/O card can convert signals from 4-6 points and implement interlocking logic through programming. In the compressor interlocking and control of the 2 # butadiene unit completed and put into operation in July 2006 at Maoming Ethylene Plant, the S7-400h system from Siemens in Germany was used to achieve overall interlocking and process control. The interlocking of shell vibration and bearing temperature was mainly achieved in bently3500. In order to achieve data sharing and interlocking redundancy, it is necessary to transmit the analog signals, alarms, and interlocking signals in bently3500 to s7-400h through communication. This article takes the control system of the 2 # butadiene compressor as an example to describe the process of implementing Modbus RTU protocol communication between Simatic S7-400h and Bently 3500.
Introduction to Control System
The S7-400 is a large programmable controller composed of power templates (PS), central processing units (CPU), signal templates (SM), communication processors (CP), and other components. The S7-400h system is a redundant system of S7-400, which achieves uninterrupted operation by automatically switching the interrupted unit to a backup unit. It can be connected to the I/O module and communication gateway of S7-400 through a local rack, or to the I/O module and communication gateway of S7-300 through ET200m distributed I/O based on Profibus DP bus, to achieve process control and communication with other control systems.
The 3500 mechanical protection system is a fully functional monitoring and protection system designed with the latest microprocessor technology. It consists of 1 or 2 power modules (3500/15), frame interface modules (3500/20), temperature monitoring modules (3500/60), displacement, speed, and acceleration monitoring modules (3500/42), relay modules (3500/32), communication gateways (3500/92), etc. The 3500/92 communication gateway is the main communication channel of the 3500 system and serves as a bridge for communication with other systems.
3 Communication scheme selection
The goal of communication implementation is to send the values of 15 temperature points and 6 compressor casing vibration points in 3500, as well as their alarm and interlock status, to S7-400h. Due to the small amount of communication data, the Modbus RTU protocol is selected.
There are two main ways to communicate between S7-400h and 3500: one is to install a CP (communication processor) on the local rack of S7-400h. S7-400h has two redundant subsystems, with CP installed on one of them. Both redundant subsystems obtain data from this CP and perform calculations in two identical user programs. Therefore, in terms of information processing in redundant system mode, it does not matter much whether the CPU is connected to the main CPU or the hot standby CPU. The disadvantage is that when a subsystem fails, the CP on the subsystem rack is no longer available. Another approach is to install the CP on a switched I/O (et200m distributed I/O), which has an active board bus and a redundant profibus-dp slave interface template im153-2. Each S7-400h subsystem is connected to one of the two dp slave interfaces in et200m. In this way, if a redundant subsystem of S7-400h fails, the CP will switch to its redundant partner, which is highly reliable and economical. We have chosen this scheme, and the communication processor uses CP341.
4. Hardware configuration and wiring of communication system
The communication processor for S7-400h is CP341, which requires a hardware dongle when using the Modbus RTU protocol. The communication processor for 3500 is 3500/92. Due to being in the same cabinet and within a distance of 15 meters, the transmission interface format has been selected as rs-232. RS-232 uses 9 pin pins and usually only uses pins 2, 3, and 5, which are used to receive data, send data, and signal ground. The interface connection is shown in Figure 1.

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