June 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 II, Definition: Identify customer requirements and complete high-level analysis of the best way to meet those requirements

CAP question

According to NFPA (National Fire Protection Association) Electrical Standards for Industrial Machinery, which of the following actions is NOT acceptable for emergency operations?

A. Using a locally supplied disconnect
B. Using an emergency stop to override all other functions and operations with all modes
C. Using an emergency switch off initiated by a single human action
D. Resetting an emergency stop circuit to initiate a restart

CAP answer

The correct answer is D, resetting an emergency stop circuit to initiate a restart.

The reset of an emergency stop circuit will not initiate a restart; therefore, the answer is not an acceptable emergency operation and is the correct answer.

Emergency stop to override all other functions and operations with all modes is an acceptable emergency operation, per NFPA 79 - 9.2.5.4.11.

Emergency switching off initiated by a single human action is an acceptable emergency operation, per NFPA 79 - 9.2.5.4.1.

Using a locally supplied disconnect is an acceptable emergency operation, per NFPA - 10.7.5.1.

Reference: NFPA. NFPA 79, NFPA. 2002.

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

If the pressure drop (delta P) across a valve increases, the velocity of fluid through the valve will normally:

A. Decrease
B. Increase
C. Remain the same
D. Change direction

CCST answer

The pressure drop refers to the change or drop in pressure from the upstream side of the valve to the downstream side. If there were no difference in pressure, the stuff would just lie there in the pipe not moving. Therefore, to move something through a pipe there has to be pressure, and the content of the pipe moves from the high-pressure end to the low-pressure end. Intuitively, one can work through this and see as the pressure difference gets larger and larger, more material moves through the pipe and the valve. Since more is moving through the pipe and across the valve, it must be moving faster and therefore the velocity is increasing-answer B.

Mathematically, this argument manifests in this equation for volumetric flow across a valve.

pg70 int june08

Q is volumetric flow, and its units are meters cubed over time (m3/sec). Av is the cross sectional area of the valve (m2), P is pressure in Pascals ((kg•m)/(sec2))/(m2), and ρ is density of the fluid (kg/m3).

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