August 2008

Documenting skills is value-add

ISA certification provides an objective, third-party assessment, and confirmation of a person's skills. It gives manufacturing and
factory staff the opportunity to differentiate themselves from their peers and gain recognition. InTech covers two certification areas in this monthly Certification department.

ISA Certified Automation Professional (CAP) program

Certified Automation Professionals (CAPs) are responsible for the direction, design, and deployment of systems and equipment for manufacturing and control systems.

The following question comes from the CAP study guide, Performance Domain III, System Design, Design, specify, and procure the hardware/software used in the system

CAP question

Which of the following standards applies to the development of embedded software for a SIL 3 certified safety system?

A.ANSI/ISA S84
B.IEC 61511
C.IEC 61508
D.21 CFR Part 11

CAP answer

The correct answer is C, IEC G1508.

According to IEC 61511-1, embedded software, which is part of the safety device/ controller, should follow software guidelines in IEC 61508-3. IEC 61508 is "Functional safety of electrical/electronic/programmable electronic safety-related systems." IEC 61511 and ANSI/ISA84 are systems standards, not product standards. 21 CFR Part 11 is not relevant as it deals with electronic signatures.

SIL is Safety Integrity Level. ANSI is American National Standards Institute. IEC is International Electrotechnical Commission, and CFR is Code of Federal Regulations.

Reference: IEC 61511, IEC, 2003

ISA Certified Control Systems Technician (CCST) program

Certified Control System Technicians (CCSTs) calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables.

This question comes from the Level I study guide, Domain 3, Troubleshooting. Level I represents a professional who has a five-year total of education, training, and/or experience.

CCST question

An instrument calibration error comes to your attention. Your analysis of the calibration plot determines that __________ and the instrument does, in fact, need recalibration.

A. there is a zero error
B. there is a span error
C. there is both a zero and span error
D. there is a linearity error

CCST answer

Span error is the difference between the actual span and the ideal span. On an input/output calibration graph, span error has an as-found line that is not parallel to the ideal line. The slopes of the two lines are different. That is the case here, and the correct answer is B.

Zero error on an input/output calibration graph has an as-found line that is parallel to the ideal line. The zero error may produce a constant offset throughout the range of the instrument.

Linearity error is only a measure of the straightness of the line and not the slope of the line. A system with gross sensitivity errors can be linear.

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Nicholas Sheble (nsheble@isa.org) writes and edits Certification Review.