December 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 III, System Design: Design, specify, and procure the hardware/software used in the system.

CAP question

Which fuse has the quickest response to over currents?  

A. Single-element   
B. Dual-element   
C. Time-delay   
D. Dual-element time-delay

CAP answer

The correct answer is A, the single-element fuse.  In electronics and electrical engineering, a fuse is a type of over current protection device. Its essential component is a metal wire or strip that melts when too much current flows. 

When the metal strip melts, it opens the circuit of which it is a part, and so protects the circuit from excessive current.

Fuses are fast-blow, slow-blow, or time-delay according to the time they take to respond to an over current condition. The selection of the characteristic depends on the protected equipment.

Semiconductor devices may need a fast or ultrafast fuse for protection since semiconductors may have little capacity to withstand even a momentary overload. 

Fuses applied on motor circuits may have a time-delay characteristic, since the surge of current required at motor start soon decreases and is harmless to wiring and the motor.

Single element fuses have a very high speed of response to over currents. They provide excellent short-circuit component protection. 

Dual-element and time-delay fuses serve in circuits subject to temporary motor overloads and surge currents. Dual-element and time-delay fuses contain two series elements-a short-circuit element and an overload element.

Reference: Bussmann Cooper Industries, SPD Electrical Production Handbook, 1992; Wikipedia


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

A beveled orifice should form an angle of:

A. Not less than 30 degrees to the axis of the pipe  
B. Not more than 30 degrees to the axis of the pipe  
C. Not less than 45 degrees to the axis of the pipe  
D. Not more than 45 degrees to axis of the pipe

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CCST answer

The orifice plate inserted in the line causes an increase in flow velocity and a corresponding decrease in pressure. The flow pattern shows an effective decrease in the cross section beyond the orifice plate, with a maximum velocity and minimum pressure at the vena contracta. 

The vena contracta is that area of the flow stream at its minimum size, where fluid velocity is at its highest level and where fluid pressure is at its lowest level, and it occurs just downstream of the actual physical restriction.

This flow pattern and the sharp leading edge of the orifice plate that produces it are of major importance. The angle of the bevel should not be less than 45 degrees. The best answer is C.

Reference: Instrument Engineers Handbook: Process Measurement and Analysis, CRC Press and ISA Press, 2003


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

What instrument should a tech use to check the quality of an electric motor's insulation resistance?

A. A megohmmeter
B A multimeter
C. A volt-ohmmeter
D A light meter

CIMM answer

The megohmmeter is a specialized type of ohmmeter designed to measure three properties of motor electrical insulation: resistance of each winding, resistance from each winding into ground, and resistance from winding to winding. 

A high electric potential is applied to the test points to test the dielectric strength of the insulation. The resistance of each winding should read very low on the ohms scale, while the resistance between windings and from each winding to ground should read very high on the meg ohm scale.

The correct answer is A, a megohmmeter.

Reference: William L. Mostia, Jr., PE; Troubleshooting: A Technician's Guide; Research Triangle Park, NC; ISA Press, 2000

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