Safety-related control systems processing unit

The transmitted signal characteristics are defined in the standard (Subset 036). A 27.095MHz tone must be generated and transmitted to the antenna. The transmitter chain allows a gain control from the digital processing unit. In order to accomphsh safety requirements, apart from the main chain, extra blocks, as the circuitry of the BIST module, have been included to add the self-test capability to the transceiver. All the blocks of the system are shown in Figure 1, where the non shaded part represents the transceiver chain blocks, and the shaded part frames the BIST related components. 

When using certain gases, it is desirable to maintain them at a set temperature for reasons related to the process and for safety. To do this, there are a number of different types of chillers and heaters. Circulating temperature controllers, use a temperature controlled liquid that is circulated through clam shell t)q)e jackets or coils placed around the cylinder. This type of system can have the actual control unit in a remote location and can easily be used in areas classified as hazardous. Another t5q)e controls the temperature of the air that is circulated through the cabinet. The air either transfers to or absorbs heat from the cylinder. Also available to heat cylinders are electrical resistance t5q)e devices. Some of these electrical devices cannot be installed into areas classified as hazardous. 

In the United States, the Center for Chemical Process Safety (CCPS) is primarily responsible for establishing H RA guidelines. CCPS developed Guidelines for Safe Automation of Chemical Processes," which established criteria for the H RA related to control and safety systems. In the United States, the International Society of Automation (ISA) is primarily responsible for establishing standards in the field of instrumentation and controls. The ISA SP84 committee developed ANSI/ISA-84.01-1996. 

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