Digital systems are great when they work, which is the case most of the time. However, many people have encountered the need to reboot or repair a mobile device, computer, or, more importantly, when the digital controls stopped working. Sometimes these problems are a minor inconvenience or cause minimal loss of productivity, but for critical systems, such failures have far greater consequences.
Industrial automation systems are designed to produce products, minimize waste, protect equipment and ensure worker safety – and must do so for a long time with minimal supervision. One definition of resilience is the ability to adjust or recover from a change or adverse effects. Most agree that the resilience of automation systems is desirable. But how to achieve it and at what price?
Since automation systems consist of sensors, cabling, power distribution, controls, networks, software, etc. unique but interconnected, the most appropriate resilience solution for any application involves many considerations and compromises.
Product knowledge and practical automation practices can help system designers to find the right balance between sustainability, cost and complexity.
The products and processes help design
In many industries, the fields of electrical engineering, instrumentation and control (EIC) are grouped together because they are closely related. Electrical includes power distribution systems and wiring. The instrumentation refers to sensors used for monitoring the state. The control includes equipment and programming necessary for the automation system running on physical devices, and extends to interconnecting programmable logic controllers (PLC), human machine interfaces (HMI) and other commonly used components for industrial automation.
Intelligent design EIC is essential for a robust and reliable automation equipment and industrial processes and covers many aspects of each project. When choosing products EIC, it is important to:
- select products designed to survive the target environment in which extreme temperatures, moisture, dirt, electrical interference and other threats may occur;
- ensure that suppliers of products focused on the test equipment in adverse conditions;
- check for relevant industrial certificates, such as Underwriters Laboratories (UL) or American Bureau of Shipping (ABS);
- select equipment with characteristics or design features that allow them to function well in tricky conditions.
reliability of reserve for automation
Designers often determine the worst that a device operating environment may encounter. However, selection of equipment tested by the supplier for their resistance to the expected operation of extreme conditions will bring an extra margin of reliability (Figure 1).
There are many credit rating agencies that provide certifications or third standards depending on the type of equipment or operating characteristics, such as voltage and the application where it will be used. Choosing UL certified equipment for industrial automation in use or with ABS certification for use on ships provides an additional guarantee of reliability.
Designers can also choose devices that offer additional integrated protection against specific problems in industrial environments including electrical interference. The input controllers / output (I / O) standard unidirectional use the simplest signaling and least expensive, but may not work as expected when they are near equipment such as welders, transformers, generators and inverters which generate significant electrical interference. . Selecting modules that provide I / O differential, signal accuracy is ensured by eliminating any electrical interference on the line in these high EMI environments (Figure 2).
robust automation systems can not provide reliable products only if they are implemented using the right procedures. Even for general automation, designers must follow regulations such as the National Electrical Code (NEC) and the ANSI and ISAs, to ensure compliance with the minimum requirements.
Individual design procedures in parts to specific areas may not provide the best overall reliability. The regulations, standards and specifications are often based on minimum requirements to meet safety requirements and basic performance. Designers must address resilience to micro and macro levels.
Reliability, redundancy and sustainability
Robust systems are designed and built using reliable products and in some cases, redundant configurations. It is useless to try to create a system resilient from unreliable components. Although the devices offer the required reliability, there are procedures for design, redundancy and installation, which can increase the resilience of the system.
The key strategy may be redundant, that is to say the duplication of system components to increase the reliability that applies to different parts of the CIS system to varying degrees. However, redundancy increases costs, equipment and the implementation of requirements and may not be practical for small systems.
For the most critical systems, the power can be supplied by the primary and secondary circuits, with or without automatic switching in the event of failure of a single circuit. The double circuit also facilitate the maintenance of power by the workers.
Numerous automation systems include an uninterruptible power supply (UPS) in key locations such as control panels. The inverter can provide AC or DC power to the downstream equipment in case of power failure. The UPS also provides a degree of filtering to improve food quality downstream devices and can signal to the control system if a problem occurs so users can react. The protection against power surges, especially for power cables and instruments, protects the expensive electronic equipment against power surges or lightning.
The equipment, cables and connectors must be installed in housings and conduits to provide mechanical protection, vibration resistance and, in some cases, a shield against electromagnetic interference (EMI) and radio frequency (RF). EMI and RF are particularly problematic for the son and cables for communication and digital signage at low voltage. These circuits must be designed and installed to ensure the distance from the power circuits that generate interference. The fiberglass enclosures can protect equipment from the elements, but a steel casing grounded offers these devices additional protection against EMI / RF.
Two instruments can be installed at critical measurement points for redundancy. Sometimes the devices are the same, but it is still better to install different technologies. The configurations of two three offer a measure of reliability even greater. For example, a high level in a tank may be measured using a primary ultrasonic transducer and a secondary transducer immersion, with high level and low level switches providing additional protection.
Industrial controllers are very reliable and some platforms offer a processor redundancy. For many medium and small systems, the cost and complexity of redundant controllers are not justified. It may be more productive to focus on industrial networks, as they are more prone to failures because they extend beyond the protected switchboards, sometimes over long distances and often in factory environments difficult. With the right equipment, it is possible to design networks in a ring configuration self-healing. The ring is installed on the path of the device or object and can withstand a single point of failure and alert the operator in case of problems. This will solve the problem before a second failure occurs that could disable the network.