MAR-APR 2018

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CCST question When using the parity system to detect transmission errors, the parity bit is set to a "1" or a "0" based on the content of the: A. bits in the data word B. start bit and bits in the data word C. bits in the data word, including parity D. bits in the data word, parity, and the stop bit CCST answer The correct answer is A, "bits in the data word." Parity is a simple method using a binary code ("1" or "0") to detect data transmission errors by making the sum of the "1" bits in the source data either an odd or an even number. The calculated parity bit is then appended to the end of the data stream. For example, if the following data word is to have "even parity," the parity bit would be set to "1" in order for there to be an overall "even number" of bits set to "1": 1 1 0 1 1 0 1 parity bit = 1 The resulting data, with the parity bit, would be: 1 1 0 1 1 0 1 1 (total of six "1" bits). The receiving device strips off the parity bit, recalculates the parity, and compares the result to the parity bit received. If it matches, it is assumed that the received data and the sent data match. If not, an error (parity error) is flagged. For com- munication to occur, both the sender and receiver must be configured for the same sense of parity (both odd or both even). Since there are five "1" bits in the origi- nal word, the parity bit for "odd parity" is a "0." Reference: Goettsche, L. D. (Editor), Maintenance of Instruments and Systems, Second Edition, ISA, 2005. CAP question How are the maintainability and mainte- nance of automation systems related? A. Maintainability is a front-end, design outcome; maintenance is related to on- going system availability. B. Maintainability is related to system availability; maintenance is related to traceability and warranties. C. Maintainability is a front-end engineer- ing function; maintenance is an ongoing engineering function. D. Maintainability is related to malfunc- tions; maintenance is related to service quality. CAP answer The correct answer is A, "Maintainability is a front-end, design outcome; maintenance is related to ongoing system availability." Maintainability is the probability that a de- vice will be restored to an operating condi- tion within a specified period when main- tenance is done with prescribed resources and procedures. It can also refer to the in- herent characteristic of a design or instal- lation that determines the ease, economy, safety, and accuracy with which mainte- nance actions can be performed on it. As such, maintainability should be ad- dressed during the front-end engineering and design phase of a project, so these characteristics are built in to the process. This includes addressing items like acces- sibility for removing pumps, piping, and instruments; complete documentation and procedures; availability of spare parts; personnel training and qualification; and suitability for purpose. Maintenance is what is performed on a system to ensure that it remains in good working condition, but also, if a failure should occur, maintenance is the mecha- nism used to return the system to the pre- vious working condition. Reference: Trevathan, Vernon L., A Guide to the Automation Body of Knowl- edge, Second Edition, ISA, 2006. Certification Review | association news INTECH MARCH/APRIL 2018 41 Certified Automation Professionals (CAPs) are responsible for the direction, design, and deployment of systems and equipment for manufacturing and control systems. Certified Control System Technicians (CCSTs) calibrate, document, trouble- shoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. ISA Certified Automation Professional (CAP) program ISA Certified Control Systems Technician (CCST) program

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