For managing a transportation network as extensive as that of TGI, it is necessary to have a data transmission system allowing control, monitoring and supervision from a control center of the critical parameters of the process, such as pressures, temperatures, consumption , and so on. One such system is called SCADA (Supervisory Control and Data Acquisition), which means Supervisory Control and Data Acquisition. A SCADA system fulfills two basic functions: Safety pipeline and Efficiency in the Operation. Pipeline Safety: The system continuously monitors and verifies the operation of critical variables such as; Pressure, temperature, alarms, etc, allowing remote valve closing when necessary. In this way, operators can take preventive and corrective actions to prevent or minimize any incidents.
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Efficiency in Operation Efficiency in Operation: The system automatically sends to the Control Center the information from the hourly and daily volumes of each consumer. From this data the computer takes the flow at different points in the pipeline increasing reliability in the measurement and avoiding the necessity of having to physically travel to the sites. A SCADA system consists of a set of components and devices that have hardware and software, which can be classified into four levels; Instrumentation, Remote Terminal Units (RTUs), Communications and Control Center . Here we give a brief explanation of each.
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Instrumentation Level This level takes the physical variables (pressure, flow, and the signals that can be read or interpreted by the operator. In the specific case of the SCADA system, it handles electronic instrumentation; hence the physical variable becomes an electric signal, (usually 4-20 mA current or a voltage of 1-5 volts). For a pipeline to basic signals monitored are: pressure, temperature, flow and the state of the valves line.
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Level Remote Terminal Units RTUs The Remote Terminal Unit, RTU, is a intelligent microprocessor device that collects, stores and processes information that comes from the instrumentation in the field. The RTU consists basically of three parts: the input and output, the CPU and the communications. Input / output consists of a series of cards of various types according to the signal that is going to receive. The CPU is the smart part of the RTU; Based on processor model 80186, 80386, 6800, or more advanced. There are also RAM, PROM and EPROM memories, which have several preprogrammed modules that permit calculations controls, commands, and other which can handle the processes required. Finally there are communications ports whose function is to take the information into digital form and place it in a port (usually type RS232, similar to a computer PC) to be subsequently transmitted to the control center through the Communications Level.
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Communications Level It is in charge of taking information from the RTU and transmits it by any means chosen to the Control Center . There are lots of communications alternatives and the choice of what is the most appropriate depends on the different circumstances in which there is the cost, availability, the transmission speed, reliability required, and so on. The following are the communications infrastructure used in the pipelines of TGI Radio Communications: Usually used radio equipment in the UHF band (ultra-high-frequency) or VHF (very -high-frequency). There should be spreading studies and have repeater stations; It is moderately expensive and provides greater reliability than the telephone line. Microwave: It is also a system of radio frequencies but in Gigahertz frequencies. It is more expensive than the previous but more reliable, it has the disadvantage of requiring line of sight to its spread, which limits the coverage distance. Satellite System: It is based on the transmission and reception through a geostationary satellite located approximately 36,000 km of land, so that there are no obstacles, and communication is continuous (except in the equinoxes where there is interruption for 5 to 8 minutes when this happens). Its reliability is high, comparable to the microwave. It is used to cover long distances and difficult coverage sites.
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Control Center Level It's made by a set of computers, peripherals and software programs that perform signal processing. Usually there is also a team of communications interface (called Front), whose function is to receive information from various channels of communications for processing and grouping and be sent to computers through LAN servers. To this network there are different devices connected to the Control Center , which consist of the following: Computer Servers: They are the main units of increased capacity and speed. They receive information from signals systems in remote locations and handles this in a large database in real time. The configuration used in TGI is the Hot-Stand by; where two similar computers are connected in parallel (over the network) so that one is the principal and the other is the backup. Consoles desktops: Are computers dedicated to the management and operation of the process. It shows in graphic details the different processes in the form of deployments and can be observed flow values, pressures, temperatures and alarms, facilitating trends, reports, analysis, modeling, etc. Other Computers: Depending on the needs, there are other computers that run software for engineering, infrastructure developments, administrative uses, training, according to the respective roles and needs of information.
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Advantages of a Scada system
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Systems SCADAs connected to the Main Control Center (CPC) TGI S.A. E.S.P.
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