1 April 2007

Certification Review

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 VI, Operations and Maintenance. Long-term support of the system 

CAP question

To simultaneously optimize an interacting dead-time dominant process with multiple constraints, one should use a (n):

A. Override PID control
B. Model predictive control
C. Decoupled PID control
D. Advisory control

CAP answer

The best answer is B, model predictive control.

Model predictive control (MPC) excels at dead-time dominance and simultaneous optimization while accounting for future prediction of proximity to constraints.

PID (answers A and C) controllers are not suitable dead-time dominance. Derivatives cannot serve, and PID controllers do not perform as well as MPCs. Override controllers select a single PID output and are not simultaneous. PID controllers simply do not work well enough. 

Decoupling is limited in practice to steady state gains and a small number of variables with no optimization built in. Operators cannot handle the interactions, the dead time, or provide minute-to-minute simultaneous corrections even if they receive regular and new set points.

Advisory control is not an entity and is therefore not the answer.

Reference: Terrence L. Blevins, Gregory K. McMillan, Willy J. Wojsznis, and Michael Brown; Advanced Control Unleashed: Plant Performance Management for Optimum Benefit; ISA Press, 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

Which of the following parts of a globe valve serves the same purpose as the disk in butterfly valve?

A. Seat
B. Plug
C. Packing rings
D. Packing flange

CCST answer

A butterfly valve has a circular body and a rotary-motion disk-closure member, which pivots on a stem, which runs up the middle of the disk. This disk with the stem looks roughly like the wings of a butterfly and thus its name. The disk physically blocks the flow of fluid through the valve body.

The parallel and the physical blocking mechanism in a globe valve is the plug. A globe valve has a linear motion, push-pull stem, and the plug closes to a seat to block the passage of fluid.

The plug and disk are both "closure members." The correct answer is B.

ISA Certified Industrial Maintenance Mechanic (CIMM) program

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.

CIMM question

P&IDs should always be kept:

A. Within easy reach
B. Locked and guarded
C. In the maintenance office
D. Accurate and up-to-date

CIMM answer

The correct answer is D, accurate and up-to-date.

A P&ID is a piping and instrumentation diagram-a schematic showing piping, equipment, and instrumentation connections within process units in oil refineries, petrochemical and chemical plants, natural gas processing plants, power plants, water treatment, and similar plants.

Plant documentation should be current. After any process revisions, the plant manager must completely document the revisions. Additionally, any documentation errors discovered in the field must reflect in and update to the original drawings. This will always save time when troubleshooting equipment failures.

Reference: Job Training Systems Inc., Reading a P&ID, Unionville, PA. JTS Inc., 1999.


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