Programmable Logic Controller & Distributed Control System Yoon-Je Choi 17 th June 2006
Programmable Logic Controller? l l Microprocessor, RAM, ROM A small computer for the process automation l l Special Input and Output l l l Connection between PLC and Sensors, Actuators Read limit switches, temperature indicators, the positions of complex positioning systems. Drive any kind of electric motor, hydraulic cylinders, magnetic relays or solenoids. Built into a simple PLC, or external I/O modules with network. Less expensive replacements for older automated system. Older automated system l l e. g. Control of machinery on factory assembly lines. Hundreds or thousands of relays and cam timers. A single PLC can be programmed to replace thousands of relays.
Simple example of PLC 1 compares the measured flow to the set point, controls the pump speed as required to match flow to the setpoint PLC 2 compares the measured level to the set point, controls the flow through the valve to match level to the setpoint
Distributed Control System l Monitors and controls a whole complete site. l PLC Monitors and Controls components or parts of the site l Most of the site control are performed by PLC l DCS controls a system at higher level: l l l DCS controls PLCs which control small parts of the site. While PLCs provide automated, pre-programmed control over a process, They are distributed across a plant. making it difficult to gather data from The PLC information are usually in a crude user-unfriendly format. DCS gathers information from the PLCs and combines and formats the information l Relate to Human Machine Interface
Distributed Control System(2)
Distributed Control System(4) l A process control system l l Used to monitor and control distributed equipments with remote human intervention. Uses a network to interconnect sensors, controllers, operator terminals, actuators. Contains one or more computers for control and mostly use both proprietary interconnections and protocols for communications. DCS is used in variety of industries, including: l Electrical power grids and electrical generation plants, Environmental control systems, Traffic signals, Water management systems, Refining and chemical plants, Pharmaceutical manufacturing.
Commercial product of 4 companies l PLC l l l Advant-160, WH Teleperm Xs, Siemens Tricon, Invensys MELTAC, Mitsubishi DCS l l Ovation, WH Teleperm Xp, Siemens IA, Invensys Mitsubishi
Specifications of a commercial product l Teleperm xs, Siemens l Processor module l l l l CPU : Intel 80486 Dx 32 Mhz Data bus : 32 bit Typical Cycle time : 50 ms Typical processor utilization <50% Memory capacity for programs and data RAM : 1 MByte Flash EPROM 512 KByte Communication module l l SINEC L 2 -bus § Protocol : PROFIBUS § Data transmission rate : 1. 5 Mbaud § Cabling : Fiber optic cable SINEC H 1 bus § Protocol : Ethernet IEEE 802. 3 § Data transmission rate : 10 Mbaud § Cabling : Triaxial 50 Ω or Fiber optic cable
Specifications of a commercial product(2) l Digital Input Module l l l Number of inputs : 32 Isolation : Yes, 1 group with 32 inputs Input voltage For signal value “ 0” : -3 to +7 V For signal value “ 1” : 13 to 33 V Input current l l l Digital Output Module l l l S 430 : 7 m. A S 431 : 0. 7 m. A Delay time : typical 4 ms( 2. 5 to 6. 5 ms) Input resistance l l S 430 : approx 3. 3 kΩ S 431 : approx 33 kΩ l l Rated supply voltage : 24 V DC Tolerance range : 20 V DC to 30 V DC Number of outputs : 32 Isolation : Yes, 2 groups with 8 outputs, each Switching current : 5 m. A to 500 m. A Digital output module relay l Supply voltage for the relays : 24 V DC l Tolerance range : 20 V DC to 30 V DC l Number of outputs : 16 relay contacts Switching capacity of contacts l With resistive load : 5 A at 30 V DC l With inductive load : 1 A at 30 V DC Power supply to relay contacts : External 24 V to 250 V Service life of contacts : approx. 105 switching cycle Switching frequency l With resistive load : <10 Hz l With inductive load : < 2 Hz
Specifications of a commercial product(3) l Analog Input module, integrating l l l l l Signal ranges with module (for channels) for thermocouples/resistance temperature detectors : ± 500 m. V/PT 100 With module for voltage measurement : ± 10 V With module for current measurement : ± 20 m. A Number of channels : 8 (2 x 4 channels of same type) Measuring principle : Integrating Permissible voltage between sensor reference voltage and ground : < 60 V AC / 75 V DC Cycle time for 8 measured values : approx, 480 ms Input resistance with module for thermocouples/resistance temperature detectors : ≥ 10 MΩ With module for voltage measurement : 50 kΩ With module for current measurement : 25 kΩ l Analog Output module l l l l Number of outputs : 8 Signal ranges : ± 10 V/ 0 to 20 m. A Load impedance For voltage outputs : min 3. 3 kΩ For current outputs : max 300 Ω Conversion time : 1 ms Short circuit protection : yes Short circuit current : max 25 m. A
Progress of Survey on PLC&DCS l l Specification of important H/W modules in PLC made by 4 companies. IEEE std 7 -4. 3. 2 TM l l IEEE Standard Criteria for Digital computers in Safety Systems of Nuclear Power Generating Stations. EPRI TR-107330 l Generic Requirements Specification for Qualifying a Commercially Available PLC for Safety-Related Applications in Nuclear Power Plant
Future work l l l Complete survey on specification of DCS H/W of 4 companies. Compare H/W spec. to requirement and EPRI TR. Make a Conclusion.
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