SCADA is a supervisory control and data acquisition software. The SCADA systems collects industrial PLC (programmable logic controller) or HMI (human machine interface) equipment information in real-time. The context for the SCADA system is the DCS (distributed control system) inside the ICS (industrial control system). Monitoring data in the production control using communication networks, controlling setpoints, recording in a database, generating reports and processing specific applications scripts.
Automation has come to optimize and make jobs easier. SCADA systems helps both the operator and the manager to control the process. Several loop repetitive tasks are automated and more time is left for decision tasks. SCADA in industrial automation is widely used. When talking about industrial automation, PLC, HMI, is also usually involved an SCADA system. SCADA is a supervisory system where real-time industrial information is gathered through a communication network. The equipment in a factory may have a communication ability. It allows PLC equipment to send the data acquisition to computers in a company. These computers, that have a SCADA system installed, allow you to receive the data acquisition from the equipment.
But it's not just monitoring. The SCADA systems can control, record, generate reports and develop specific applications from the data acquisition. In the case of the control, the PLC may contain variables. Setpoint, limits, and parameters in general. Then the SCADA sends the data to the equipment and it has its data parameterized. Each variable or information is usually called a tag. In a SCADA software these tags can be memories and formulas as well. The equipment that communicates with the computer is usually a PLC. PLC is an acronym that stands for Programmable Logic Controller. There may be a lot of equipment on the same communication network. All these equipment may be gathered in the SCADA system. The most commonly used communication types in the data acquisition are ethernet and serial. For the case of serial communication may be RS-232, usually standard DB9, or RS-485. The RS-485 allows multiple devices on the same line and a longer distance, so it is widely used. Ethernet is the format of the computer network generally used with the TCP protocol in the SCADA systems.
For the case of ethernet communication, each equipment / PLC has an IP. These devices can communicate directly with the computer over a specific network or through the corporate LAN network. There are several types of communication protocols. In the case of serial communication, one of the protocols used in SCADA systems data acquisition is the MODBUS RTU. This standard has been set to the SCADA system sends and receives data from a generic address table. A similar protocol can be used via ethernet which is the MODBUS TCP. Each device may have a specific communication protocol. For the SCADA system to communicate with the equipment, a communication driver is required. This driver is a part of the software or library that allows you to communicate with the equipment. But a driver that communicates with MODBUS RTU may be used in equipment that has this protocol.
Keep the factory under control in real time, keep reports and analyze everything that has occurred. This is one of the characteristics of an SCADA software system. Each control point, each system tag.
Monitoring information in an HMI SCADA system (human machine interface). An HMI screen is designed like a panel with buttons, displays, gauges, charts, etc. Data is presented to the user in a SCADA software.
Display: objects that display values on the SCADA HMI screen. Several formatting properties can be used. Numbers, texts, and even colors indicative of errors and alarms. They are mainly associated with analog tags.
Pictures may be used in the HMI not only to illustrate the environment or the machine but also to represent buttons and states. For example, open or closed valve, also associated with a tag. The pictures can be animated, as in the case of running engines as well. Instead of external pictures, it is possible to draw on the SCADA itself. Vector drawings are also used as objects.
Buttons: Used to receive a user command. By clicking on the button, an action is triggered. Information sent to the PLC, change of HMI panel or report generation. These buttons may be hotspots distributed over a picture on the HMI in a SCADA system.
LEDs: color indicators for digital states. If a digital variable of the PLC is connected, value 1, then the color referring to the connected state is activated in a LED.
Gauge: pointer indicator for analog SCADA system variables. The minimum and maximum values of the scale are set. Limits may also be placed.
Level: Level indicators with scale. They can be used from liquid indications such as in tanks to simple scales of analog numbers. The minimum and maximum values of the scale are defined. SCADA system alarm and safety limits can also be set.
Check: key switches on and off. They are associated with digital tags. When the user clicks the SCADA HMI on the check a digital signal is sent to the PLC.
Text/number input: Components for number or text entry. Usually used in analog variables. The user enters the value in HMI and sends the variable to the PLC. Combos can also be used to stop preset values. Text may be used as information also, for example, product name.
Chart: Charts are important to show the behavior of the tags over time. They may be placed in a HMI associated with the PLCs tags. In the Y axis the tag values are placed, and in the X-axis, the time. This history may be saved to the database.
Control: The setpoints available in the system are controlled by the SCADA system. Limits and presets are changed during the process. Valves, pumps can be also triggered by the SCADA systems.
Data acquisition: Information from the PLC transmitted to the computer as explained above. Data acquisition and reporting may be continuous or split by testing or production. For the continuous case, the data is monitored continuously with some possible interruptions. In the case divided by test, there is a beginning and an end. It could be a calibration, an inspection, or even a small production.
Database in SCADA
The database stores the history of the information collected by the PLC. They may be binaries, texts, standard formats via ODBC or proprietary. These databases have fields that can be created according to each case. Auxiliary tables are also used to feed information. Each field in a database may be a tag. Each database has multiple tables. Each table has records separated by date. Field types can be number, text, or date/time. Tables may be protected by a password or by a CRC so the data can not be changed without permission there. The table data is searched by filters on the fields. For the case of the ODBC, they may be queried via SQL in the application.
Reports in SCADA
Generating reports is often the goal. They are where the final results are presented. They are documents with formatting from headers, texts, and footers. The data in the reports are presented through texts, tables or graphs. Each report format is defined according to each system case. The data stored in a SCADA system are filtered according to each case and placed in the tables. The data can be presented by time or by crossing information. Likewise the charts. There are several types of analysis that may be done in reports. Means of values, count of items, control of users that changed setpoints, tests of values that exceed limits, quality reports, efficiency, production statistics, etc. Reports can also be test results as a certificate. Data headers for a product, customer, procedures, collected data and calculated results using the acquired information. This reporting may have specific standard layout approved by the quality sector.
SCADA distributed system
SCADA system can be distributed. Several computers in a network can receive information from the equipment. This data sharing can be via WEB / TCP. In a computer network, some computers with SCADA are connected to the PLC / equipment. These computers become servers. Other client computers on the network receive the information from the servers. Similarly, data written to the database is stored on servers. Reports may be generated on the client computers with the data retrieved from the servers. This network can be LAN network. Each computer can have an IP.
Scripts are used for specific applications with sequential commands. These commands are defined within each system event. This script can be a computer language. A sequence of commands and conditions that define the behavior of specific processes. Also, some more advanced calculations that must be addressed by algorithms.
Examples of SCADA commands:
Transfer value from a tag to a variable: The value of the tag, an analog or digital output point of a PLC, is transferred to an internal script variable. This variable is used to calculate results or define other behaviors. Set values of a tag: Specific values of equipment entry points may be set via script depending on the behavior of an event or some state. Conditions: Define conditions to execute a command. Example, if a tag is greater than other, then execute some command.
There are many types of events in a SCADA system. Examples of events:
After the scan: executes a series of commands after the values of the tags have been read from the PLC. Alarm: Run a script when an alarm is triggered. Start: Run commands when the system starts. Clicking an object. Execute commands when the user clicks on any of the objects in the HMI.
There are also several types of auxiliary SCADA commands that are used in script.
Text commands, where text variables are handled with formats and positions. SCADA commands for handling numbers, logical commands, rounding, mathematical calculations, timings, handling of time variables, commands for writing to special files (text/binary), commands for TCP communications, etc.
There are two basic types of SCADA variables in script. Text variables and numeric variables. Text variables are used, for example, for status and warning statements. Numerical variables can be analog or digital variables.
Building automation: A housing complex or a hotel can have a centralized control. There are many things to control and monitor. The number of lamps to be turned on and off can be huge, and schedules may be made from on and off times. Also, if you want, a control of who left it on and for how long. And it's not just the lamps, but the air conditioners as well. Control for on, off and schedules. Another fundamental thing in SCADA is the control of energy expenditure. Voltage, current and power data must be monitored. There is also the case for open and closed door security systems for apartments. And pumps for swimming pools and saunas.
Water treatment: For the case of water treatment, there is a sequence of steps. Chlorination, sedimentation, aeration, sand filtration, disinfection, etc... The SCADA system can monitor the liquid level of each stage. The valves can also be opened or closed by SCADA. In a HMI, all the steps in the schematic with tanks, pipes, motors and valves may be monitored. In the database and report the history of pH, temperatures, flows, oxygen and levels are controlled with samplings and charts.
Temperature control: For temperature control, several points with thermocouples can be distributed in the plant. Each thermocouple sends the information through indicators or controllers. Each temperature point has tolerances relative to the process. In some cases, a recipe of pre-set temperatures should be followed. For these cases, temperature controllers with analog outputs or relays are used to heat or cool the system. Recipes and setpoints may be controlled via SCADA.
Production control system: In production control, many items should be controlled. Each machine can be used by several operators. Each operator will act in specific shifts. The machine will be switched on for production and shut down for various reasons. The machine on and standby time must be monitored. When stopped, the reason must be related to the SCADA system. When in production, the pieces must be counted. The reports may contain the relationship between the operators, the running time of the machines, the reasons for the stops and the counting of parts and the characteristics of the products.
Product test: A product test has a middle and an end start. It can be divided into several phases. At the end, a report is issued with product data, data collected and results. One example is the vehicular inspection. First, the vehicle and customer data are entered. Then the suspend test is started. Vibration variation is monitored and stored. Then the braking test is performed. The braking force is stored. Then, in the generation of the report, the factors that, based on the data collected, will be calculated if the vehicle has passed or not passed the test.
One very important item that is being analyzed is the safety of SCADA. The SCADA system can not allow data to be manipulated by undesirable sources. Various types of actions must be taken to ensure that only the chosen users are able to control the system.
Easier jobs with the SCADA system.