The hottest pakscaniie double line control system

Application of pakscaniie double line control system in cis-1,4-polybutadiene rubber plant

in order to improve the deep processing of petrochemical products and the development of new products, and increase the economic benefits of the enterprise, Daqing Petrochemical Company carried out the phase II reconstruction and expansion of the ethylene plant with an annual output of 300000 tons and an annual output of 480000 tons. As one of the top projects of the second phase reconstruction and expansion project, the annual output of cis-1,4-polybutadiene rubber has achieved an annual material saving of up to 20% and 50000 tons. The cis-1,4-polybutadiene rubber plant was completed in November 1997 and has produced qualified products In this device, the two position on-off valve accounts for a large proportion of the regulating valve. Our factory selects the electric actuator produced by UK Rotork Control Co., Ltd. and introduces its Pakscan IIE double line control system for local control of the device

2. Introduction to Pakscan IIE double line control system

this system is an intelligent control system based on electric valve actuator There are three elements in the system: field unit, double line circuit and main workstation

in a two-wire control system, the main workstation can control 240 field devices within a distance of 20km, collect important digital and analog data of field actuators, and the scanning cycle is 1.89 seconds There is no distance limit between nodes, and no repeater is required

Rotork also has a data collection and control transmission unit similar to Pakscan field unit and compatible with Pakscan protocol. Field equipment such as transmitters, solenoid valves, pumps and agitators from other manufacturers can be integrated into the Pakscan dual line control system

the connection between two-wire circuit and actuator is very simple The cable is an easy to install fully shielded twisted pair, which has the advantages of easy installation, easy maintenance, low cost and high efficiency in all applications

two wire cables are connected in or out of each actuator in sequence. They originate and return to the main workstation to form a two-wire loop Because each field device is connected in two directions, it forms a redundant communication line

as the core of the two-wire control system, Pakscan IIE main workstation has a modular structure, which is a rack assembly composed of a computer card, a current loop interface card, a power card and a panel with LCD screen and 16 key keyboard

as the basic field equipment of the two-wire control system, Rotork actuator family includes IQ, a, AQ, Q and other series products, which are intelligent actuators with modular structure design, integrating interlocking solenoid valves, valve position travel switches, and analog valve position transmitters

in order to complete different work needs, it is only necessary to replace field unit modules with different functions in the actuator. There are Pakscan now Yang unit, follomatic (valve position proportional control) unit, data recorder unit and current 1 through the implementation of circular economy, society torque transmitter unit, etc

3. Working principle of Pakscan he two-wire control system

the main workstation and field control unit (FCU) communicate through a two-wire current loop. During work, the main workstation continuously checks the integrity of the cable circuit. In case of power failure or failure of a field unit in the circuit, the smoothness of the line will not be affected

see Figure 1 for the normal operation of the double line control system

during normal operation, the main workstation detects the field unit by address during the scanning cycle. Always keep communicating and exchanging data with the field unit nearest to the a port of the two-wire circuit, and then communicate with the next field unit nearby. After communicating with all field units in the circuit in turn, start the next scanning cycle

in case of cable open circuit, short circuit or grounding fault, the field units on both sides of the fault point can form a return path

see Figure 2 for the operation of circuit open circuit fault

the main workstation first arrives at the first field unit connected to it from port a and instructs to remove its own circuit. In this way, the current loop can be continuously extended until the fault point is found. Then remove the circuit of the field unit from port B in the other direction until the fault location. After finding the fault location, the main workstation instructs the front and rear field units connected to it to determine the circuit to maintain the normal operation of the whole system

4. Application

in the rubber device, a total of 68 Rotork electric actuators enter the Pakscan IIE double line control system. We fully develop the advanced functions of the system, especially the valve position adjustment function, and complete the general two position switch control, precision batch control and interlocking liquid level control under the intervention of DCS

the main production process of cis-1,4-polybutadiene rubber plant is controlled by Honeywell TPS DCS system. In order to facilitate the operation of process personnel and realize the optimal control of the whole plant, we will communicate the two-line control system with DCS, and the work instructions of field actuators will be issued by DCs. In fact, IIE main workstation only acts as an interface with data processing capability. See Figure 3 for the interface between the two systems

the main workstation communicates with the TPS DCS system through the RS485 interface of the serial interface card (SI) in the HPM. DCS uses array points