DCS Control System. A DCS (distributed control system) is a manufacturing or process control system in which the controller elements are not centrally located, but distributed throughout the system with each sub-system controlled by one or more controllers. The entire system of controllers is connected by networks for communication and monitoring. The processor receives information from input modules and sends information to output modules. Input modules receive information from input instruments in the process and output modules transmit instructions to the output instruments in the field. Elements of a distributed control system may directly connect to equipment such as switches, pumps, and valves. DCSs control manufacturing processes that are continuous or batch-oriented, such as oil refining, petrochemicals, central station power generation, pharmaceuticals, food & beverage manufacturing, cement production, steelmaking, and papermaking.
Things to Consider: System redundancy features, Source control components from one manufacturer, Other components from other manufacturers need to be evaluated for compatibility, Modular design, Operating temperature range -40 to +70 degrees C, Storage temperature range -40 to +85 degrees C, Humidity (non-condensing) rating 5 to 95%, Clock for time stamping and scheduled reporting, Clock must operate through power outages, High data throughput and fast program execution, Flash memory for fimware and application program storage, Fast dynamic memory for efficient program execution, Data logging memory that can be retained through power outages for minimum 30 days, Non-volatile memory sufficient for 8000 variables to be maintained through unplanned and instantaneously occurring power outages, time and event data logging, Mean Time Between Failure (MTBF) at acceptable time period, Two independent yet redundant power supplies, Power supply inputs of different voltages, One supply can be a battery while the other is powered from the mains, Control modules must accept DC power 10-30 VDC, Power LED for each input source, Power supply compliant with IEC 92-504 (failure and variation), number of local channels, number of remote channels, number of networked channels, analog inputs, I/O modules to be removeable and replaceable with system powered up, controller port configuration, serial port availability, master and slave configurations, Peer-to-peer I/O transfers, Serial modem support, True multitasking, Ability to add I/O drivers to support third-party equipment, Local and remote configuration during operation, Com ports configurable by standard included software, Windows based programming software, Electrical safety compliance: UL508, CSA C22.2/14, EN61010-1 (IEC1010-1), IEC 950: 1950, AS/NZS3260-1993, CE, Flammability: UL94v rating, EMI Emissions: FCC part 15, ICES-003 Class A, En55022, AS/NZS3548-1995 EMI emission standards, CE, EMC Immunity: EN50082-1 (IEC801-2 3 4), EMC immunity standards, CE, Surge withstand: IEEE-472 (ANSI C37.90) surge withstand standard, Vibration: IEC68-2-6V vibration standard, Hazardous Locations: Class 1, Div. 2 Group A B C and D hazardous locations, UL 1604, CSA C 22.2/213-M1987, Cenelec EN50021 (EEx nA II T4) for zone 2 locations, Marine/Offshore Locations: Det Norske Veritas (DNV) No. 2.4, Warranty.
Microprocessor Control Systems. Built around an integrated computer circuit that performs all the functions of a central processing unit, these systems are used increasingly to handle control functions previously carried out by a dedicated analogue control circuit. These control systems are programmable, so that modifications or application requirements may easily be applied without redesign. They can be programmed to make detailed calculations and statistical analyses. Data logging can be done easily, so that operation is automatic, and instrument calibration is simple.
Things to Consider: Proportional band, Integral time, Derivative time, Tuning, Cycle time, On-off deadband, Anti-reset windup, Sensor break protection, Mechanical relay, SSR driver, Current output, Accuracy, Display, Memory, Self-diagnostics, Operating/Storage ambient temperature and relative humidity ranges, Power requirements, Isolation, Dimensions, Alarms, Output types and options, Input types and ranges, Ramp to setpoint control, Sealed faceplate for wash-down environments, Warranty.
PLC Control Systems. A programmable logic controller (PLC) is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. Unlike general-purpose computers, the PLC is designed for multiple input and outputs, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in non-volatile memory. PLCs are armored for severe condition (dust, moisture, heat, cold, etc) and have the facility for extensive input/output (I/O) arrangements. Functionality includes sequential relay control, motion control, process control, distributed control systems and networking.
Things to Consider: Input power, Number of inputs, Number of outputs, Maximum I/Os, Program capacity (Kbytes), Maximum analog I/O, Processing time, 32-bit & floating point capability, Modbus master and slave built-in, High speed counter frequency, Pulse outputs capabilities, Data memory, Dimensions, UL/cUL listed, CE certified, Warranty.