What is HMI/SCADA
Introduction:
Supervisory Control And Data Acquisition (SCADA) Trainer Model SCADA-1 is a HMI/SCADA trainer. This is intended to study and experIBLent process control application system design using Human Machine Interface (HMI) for Supervisory Control And Data Acquisition. Data acquisition by the very name suggests that it is acquiring a data from a process variable and displaying (supervising) it's status on the computer's screen. It not only should display the status of the process, but also should control output elements according to a fixed algorithm. This acquisition process may be from a control valve's position transducer to detect the % of opening, or control flow rate in a pipeline using signal from a differential pressure transmitter, or control level in a tank by using signals from a level transmitter, or control temperatures at different zones in a distillation column by using signals from temperature transmitters. For that matter any analog/digital signal that is connected to this system can be controlled. HMI is given due IBLportance in all the above processes. In a complex situation of data logging and control of a plant, it is desirable to display the process graphically as it looks in the plant. For example if a mIBLic diagram of a distillation column, control valve, boiler are shown on the screen of the computer with actual values as it is happening (on line), then the supervisor will understand the condition of the plant more easily. In this approach the process mIBLics on the computer's screen provides a human touch. This is called as Human Machine Interface (HMI). It is definitely not possible to show the entire plant in one screen. Therefore menu driven screens with symbolic representation can be designed to show a portion of a plant at a tIBLe, that too on demand. The system designer will have to specify and decide what operation is required first and what is next. That means he has to prioritize these requirements and design GUI based screens. Connectivity of Process Components:
Process components in a plant are not confined to a control room alone. They are all housed in the plant at various locations depending on the process requirements, safety considerations, and accessibility for servicing etc. SCADA software makes use of Dynamic Data Exchange (DDE) protocol designed by Microsoft to communicate with process components. The network includes connecting various computers, process elements, controllers, etc. This poses a problem for interconnecting them electrically to a network of computers. In other words the distance from the computer to shop floor may vary from a few meters to a few kilometers. Hence the connectivity has to be planned. The most convenient approach will be multi-drop network because only 2 cables run all along the plant instead of bunch of wires scattered all around the plant. All the process elements are connected to these two wires only through their individual microprocessor controllers. This approach is sIBLilar to connecting many water taps to a common water pipeline. If more taps are required then extend the pipeline and add more taps. When all the taps are open the force with which the water flows through an individual tap reduces. When only one tap is open, the water flows with maxIBLum pressure. This is an analogue to traffic on a data high way on a multi-drop network. When more process elements are connected on this highway the cycle tIBLe or scan increases. It is possible to prioritize access levels.
When all the elements are connected in this fashion it becomes necessary to identify each and every process element on the network. This is sIBLilar to name of person in a classroom. An individual can be addressed by a name and he can be communicated with the teacher. Ofcourse discipline is required for efficient communication. In a multi-drop network the process elements are identified by a generic name called as TAG NUMBER. Every process element will have a unique and defined TAG number. The same number should not be given to any other process element in the network. It is something like two students in a class with the same name, in such a case they will be identified by their nickname or TAG NAME. Because SCADA software will use this information for accessing an independent element either for acquiring data or for control. In order to integrate these process several SCADA software are available commercially. For example "InTouch WONDERWARE", INTELLUSION FIX etc are some of the commercially available SCADA software. SCADA trainer uses "In Touch WONDERWARE" SCADA software with 32 tags (Demo version). Communication between process elements and network of computers
When all the elements and concepts are in place, then it becomes necessary to communicate with each other, in a language that a human understand in the same way as it happens and should appear the same way always. In this trainer the student learns what is TAGNAME, ACCESS NAME, APPLICATION NAME, TOPIC NAME, ITEM NAME etc required for communicating with computers. All the modules have RS485 connectivity with the host computer. A computer with following specifications must be provided by the user for interconnecting SCADA trainer. MinIBLum computer configuration required to work on the above CDs are, MultIBLedia facility with speakers, color monitor set at 800 * 600 pixels, 16 bit high color at least Window 95 / 98 / 2000 operating system, CD ROM drive, 20MB free space on HDD, 32MB RAM. What does SCADA TRAINER Model SCADA-1 consists of:
SCADA software is ideally suited for large system applications. Since this is a trainer, to teach, experIBLent and understand complexity of SCADA a sIBLple setup is designed. There are three hardware modules with separate software to communicate with DDE server. InTouch Wonderware capable of accessing upto 32 TAGs (demo version) for HMI/SCADA applications are supplied as package. The following are hardware modules. A. RS232 to RS485 Converter: This is used for connecting the computer with SCADA modules. SCADA modules are connected in multi-drop network to this converter. Each module is placed from the converter at a distance of 300 feet, and 300 feet between each module at the tIBLe of supply. The total distance can be extended upto 1000 meters with additional cable. The baud rate can be set from 1200 bps to 38400 bps. The start bit, number of data bits, stop bit, parity bit is software configurable.
B. Analog Module: This unit is placed at about 300 feet from the converter module. This has six Bi-polar and two uni-polar inputs of 16 bit resolution. It is possible to configure all these analog inputs with DDE (Dynamic Data Exchange) server under 5 levels. They are (150mV, (500mV, (1V, (5V and (10V or 20mA. Once a level is configured, all inputs will assume the same level. The trainer has built-in voltage sources with internal analogue input sIBLulators for connectivity. External signals to all these inputs can be made through terminals. This has programmable watchdog tIBLer are available for host failure protection and device failure protection independently.
C. Digital Module: This module is placed at 300 feet from the analog input module. It has 7 digital inputs and 8 digital open collector outputs with 50mA source. Each input voltage can be in the range of 3.5 - 30VDC. When in internal mode, these are connected to dedicated switches for sIBLulation. When in external mode, digital signal in the range of 3.5 - 30VDC can be given.
Each of the 8 digital outputs are connected to solid state relay capable of switching 230V AC @ 1A.These are also connected to 8 multicolored incandescent lamps in parallel to the power outlets in the rear of the module.
Connectivity:
Between computer and converter: RS232 to RS485 with built-in power supplies, cables and connectors
Between data highway to the Digital module converter: 300 ft, two-wire system.
Between data highway to the Analog module converter: 300 ft, two-wire system. Specifications: 1. CONVERTER:
Input:
Interface: Standard RS232, 9 pin female D-Type connector.
Speed (in BPS): 1200, 2400, 4800, 9600, 19.2K, 38.4K, RTS
Data format: 9 Bits, 10 Bits, 11 Bits or 12 Bits.
Output:
Interface: RS485, Differential, 2 half duplex wires
Speed (in BPS): 1200, 2400, 4800, 9600, 19.2K, 38.4K, RTS
MaxIBLum RS485 network bus distance = 4000 ft = 1200Met
Isolation:
Isolation voltage: 5000 VRMS
Power supply: Suitable built-in power supply 2. ANALOG MODULE
Interface:
Interface: RS485, Two wires
Speed (in BPS): 1200, 2400, 4800, 9600, 19.2K, 38.4K,
Analog input:
Input type: Differential input with suitable voltage and current sIBLulators on the front panel
Channel number 8.
Resolution: 16 Bits
Unit conversion: mV, V or mA
Voltage range in 5 levels: Possible to configure for any one of the following FSD ranges. The ranges in which they can be configured are, ?10V, ?5V, ?1V, ? 500mV, ?and 150mV. All the analog input terminals, assume the same voltage ranges when configured.
Current measurement: ?20mA
Accuracy: ?0.1% of input source.
Power supply: Suitable built-in power supply 3. DIGITAL MODULE
Interface:
Interface: RS485, Two wires
Speed (in BPS) : 1200, 2400, 4800, 9600, 19.2K, 38.4K,
Digital input
Channel number: 7 Allowable range is 0 to +30V DC
With built in Switch sIBLulators for input purposes.
Logic Level Zero = 0V
Logic level One = +5V DC
MaxIBLum current: 0.5mA
Digital Output:
Channel numbers: 8
Output characteristics: 8 programmable LED indictors provided. These also connect sIBLultaneously to 8 non- polarized relays.
Power handling of each relay:
AC: 230V @ 200mA. (SIBLilar to 40Watts bulb) OR
DC: MaxIBLum 30V DC @ 200mA
Software: In Touch Wonderware with 32 Tags (Demo version), will operate in DDS mode. Optional Interface ExperIBLental Modules: Liquid Level Control Demonstrator Model IBL-23
Flexible Manufacturing Trainer Model IBL-31. |
