December 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

An application includes a VFD that implements a V/Hz method of torque control while maintaining a fixed V/Hz ratio. The motor has a nameplate rating of 460 volts and 60Hz. If the drive is operating at 30Hz, what percent of rated torque will the motor MOST likely develop?

A. 25%

B. 50%

C. 100%

D. 200%

CAP answer

The correct answer is C, 100%.

The volts-per-hertz ratio (V/Hz) controls the torque of a motor. As long as this ratio remains in proportion with the nameplate rating, the motor will develop rated torque. The only answer that represents rated torque is 100% rated torque. The other values do not represent rated torque.

Reference: Dave Polka; Motors and Drives: A Practical Technology Guide; 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

The standard range for pneumatically transmitted signals is:

A. 3-15 psig

B. 5-20 psig

C. 1-10 psig

4. 4-02 psig

CCST answer

Industry recognized early on that for the sake of ease and safety it would be better for an operator to monitor and control processes in a more convenient and protected place. The need for transmitting the process variable to that place settled on pneumatic transmission.

They used 3-15 pounds per square inch gauge (psig) as the range. The value of using three rather than zero is to detect failure of the instrument air supply. The measurement of 15 psig is for 100%, because it is well below nominal pressures for the air supply for diagnostic purposes.

dec10

The correct answer is A, 3-15 psig.

Thousands of pneumatic instruments, controllers, and control valves remain in use even today, well into the digital signal transmission age.

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