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MAR-APR 2019

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24 INTECH MARCH/APRIL 2019 WWW.ISA.ORG Safety system A risk assessment drives the safety sys- tem design as needed to remove motion- causing energy, including electrical and fluid power, to safely stop the equipment for protection of both personnel and machines. Many safety standards come into play for proper machine control at both a mechanical and electrical level. Proper mechanical machine guarding and access points, as well as elimination of identified hazards, is a starting point. Safety relays or safety-rated controllers must be used to monitor safety switches, safety limit switches, light curtains, and safety mats and edges. In small machine control applications, a safety relay is probably the simplest way to integrate safety functionality for emer- gency stop, monitoring a guard door, or protecting an operator reaching through a light curtain. In more advanced ma- chines, safety-rated controllers provide the same functions, but can simplify the integration of multiple safety devices. Safety-rated controllers reduce hard- wired safety logic by providing a platform to program the safety functions needed for proper and safe machine control. Programmable controllers and I/O Available in form factors from small to large, the machine controller can be a programmable logic controller (PLC), a programmable automation controller (PAC), or a PC. The complexity of the machine control application, end-user specifications, and personal prefer- ence drive controller selection. Many vendors have families of controllers to cover a range of applications from simple to complex, allowing a machine builder to standardize to some extent. Often three or more physical configu- rations—small, medium, and large form factors—are available from the controller manufacturer. Using the same software platform to program a family of controllers is be coming the norm. This allows the de- signer to first program the system, and then select the right controller based on its capacity to handle the number of I/O points needed, as well as special functions such as proportional, inte - gral, derivative control and data han- dling. Required capabilities like exten- sive communications and high-speed control should be carefully evaluated, as these are often the main factors driving controller selection. Discrete and analog inputs and outputs connect the controller to the machine sensors and actuators. These signals can originate in the main con- trol panel through a terminal strip with wiring to field devices, but a dis- tributed I/O architecture is often a bet- ter solution. Distributed I/O reduces wiring by moving the input or output point closer to the field device, and by multiplexing multiple I/O signals over a single cable running from the remote I/O component to the control panel. For distributed I/O at a smaller scale, IO-Link is a point-to-point serial communi - cation protocol where an IO- Link-enabled de- vice connects to an IO-Link mas- ter module. This protocol commu- nicates data from a sensor or actua- tor directly to a machine control- ler. It adds more context to the discrete or analog data by delivering diagnostics and detailed device status to the controller. Communication systems Another important part of machine control now and for the future is exten- sive communication capability. It is a good practice to have multiple Ethernet and serial ports available to integrate to a variety of equipment, computers, HMIs, and business and enterprise sys- tems (figure 3). Multiple high-speed Ethernet ports ensure responsive HMI communica- tion, as well as peer-to-peer and busi- ness system networking. Support of industrial Ethernet protocols, includ- ing EtherNet/IP and Modbus TCP/IP, is also important for scanner/client and adapter/server connections. These Ethernet connections enable outgoing email, webserver, and remote access communication functions—all impor- tant options for machine control. Machine control often benefits from the availability of legacy communica- tion methods, such as serial RS-232 and RS-485. Modern controllers often also include USB and MicroSD com- munication and storage options. A big part of machine control commu- nication is cybersecurity. Consider a lay- ered defense where protection includes remote functions that are only enabled as part of the hardware configuration. For further protection, all tags should be pro- tected from remote access unless the tag is individually enabled for that purpose. FACTORY AUTOMATION Figure 3. In addition to the multiple communication ports on this BRX controller, additional ports are added using a STRIDE Industrial Ethernet switch and a GS drive serial-to-Ethernet adapter. Figure 2. These Fuji manual motor starters and contactors from AutomationDirect have high switching capacity and integrate the functions of a molded case circuit breaker and a thermal overload relay.

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