AADvance Safety Manual - Tuv-fs.com

Chapter 6 Glossary of TermsGlossary of TermsAaccuracyThe degree of conformity of a measure to astandard or a true value. See also'resolution'.achievable safe stateA safe state that is achievable.Note: Sometimes, a safe state cannot beachieved. An example is a non-recoverablefault such as a voting element with a shortedswitch and no means to bypass the effect ofthe short.actuatorA device which cause an electrical,mechanical or pneumatic action to occurwhen required within a plant component.Examples are valves and pumps.AITAAnalogue input termination assembly.alarms and events (AE)An OPC data type that provides timestamped alarm and event notifications.allotted process safety timeThe portion of the total process safety timeallotted to a sub function of that process.application softwareSoftware specific to the user application,typically using logic sequences, limits andexpressions to read inputs, make decisionsand control outputs to suit the requirementsof the system for functional safety.architectureOrganizational structure of a computingsystem which describes the functionalrelationship between board level, devicelevel and system level components.asynchronousA data communications term describing aserial transmission protocol. A start signal issent before each byte or character and astop signal is sent after each byte orcharacter. An example is ASCII over RS-232-C. See also 'RS-232-C, RS-422, RS-485'.availabilityThe probability that a system will be able tocarry out its designated function whenrequired for use — normally expressed as apercentage.Bbackplane clipA sprung, plastic device to hold togethertwo adjacent AADvance base units. Partnumber 9904. Used in pairs.base unitOne of two designs which form thesupporting parts of an AADvance controller.See 'I/O base unit' and 'processor base unit'.black channelA communication path which has norequirement to maintain the integrity ofsafety critical data transferred over it.Measures to detect and compensate for anyerrors introduced by the channel must beimplemented by the safety critical senderand receiver to make sure the data retainsits integrity. Black Channel communicationswill typically use an Ethernet LAN, which canuse off-the-shelf components and provides aparticularly cost-effective solution.blanking coverA plastic moulding to hide an unused slot inan AADvance base unit. Part numbers 9191and 9193. Unscreened. Provides physicalprotection to base unit connectors andensures a neat appearance.booleanA type of variable that can accept only thevalues 'true' and 'false'.Document number 553630 Issue 7: February 2010 7-1