1 May 2007
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 three certification areas in its 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 I, Feasibility Study: Identify scope and justify the automation project.
Which of the following control strategies works to measure disturbances and compensate for them before they cause the controlled variable to deviate from the set point?
D. Open loop
The best answer is A, feedforward.
The objective of feedforward control is to measure disturbances and compensate for them before the controlled variable deviates from set point.
Feedback control can compensate for a disturbance only after the control variable has deviated from set point.
Cascade is a form of feedback control.
Open loop is not a control strategy.
Reference: Carlos A. Smith and Armando B. Corripio; Principles and Practices of Automatic Process Control, 2nd Edition; Wiley & Sons, 1997.
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.
The dead band of an instrument is:
A. The band that prevents the instrument from being tampered with by unauthorized persons.
B. The range of valves for which the instrument gives inaccurate readings.
C. The size of the instrument indicated by the divisions on the scale of the instrument.
D. The range that an input signal may be changed on reversal of direction without an observable change in the output.
In process instrumentation, the dead band is the range through which an input signal may vary, upon reversal of direction, without initiating an observable change in output signal. The correct answer is D.
The Automation, Systems, and Instrumen-tation Dictionary adds these notes as further definition.
Note 1: There are separate and distinct input-output relationships for increasing and decreasing signals.
Note 2: Dead band produces phase lag between input and output.
Note 3: The instrumentation industry expresses dead band as a percentage of span.
Note 4: ANSI/ISA-51.1-1979, revised 1993, pertains to dead band.
Certified Industrial Maintenance Mechanics (CIMMs) are responsible for preventive, predictive, and corrective maintenance. They are multi-skilled individuals whose expertise is primarily mechanical in nature as opposed to instrumentation or electrical. CIMMs have a minimum of five years of relevant work experience in the maintenance mechanic field or three years experience and a two-year associate degree in maintenance or a related field. This question is from Performance Domain III: Troubleshooting and Analysis.
What are two resources available to a maintenance mechanic to help verify a problem?
A. The capital plan and the installation manuals
B. The operator of the system and the equipment historical data
C. The plant engineers and the super-visor
D. The operations supervisor and his crew
The best answer is B, the operator of the system and equipment historical data.
The maintenance mechanic should always have a conference with the operator to discuss temperature, noise, pressure, flow, and other working parameters. After conferring with the process operator, check past history for a similar failure and repair.
Reference: Lawrence D. Goettsche; Maintenance of Instruments and Systems, 2nd Edition; ISA Press, 1995.
Nicholas Sheble (email@example.com), InTech's senior technical editor, writes and edits the Certification department.