November 2008

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 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

Given R= r  L/A

What is the resistance of 1,000 ft of copper wire (specific resistance  = 10.37) given a cross-sectional area of 10370 cmil and a wire temperature of 20°C?

A. 1 Ω
B. 2 Ω
C. 10 Ω
D. 100 Ω

CAP answer

Circular mil (cmil) is a unit of area, equal to the area of a circle with a diameter of one "mil." A mil is one thousandth of an inch.

In the U.S., the National Electrical Code uses the circular mil to define wire sizes larger than 4/0 AWG.

The resistance of a length L (ft) of a conductor can be determined using the specific resistance and the cross-sectional area A (cmil) by using the equation R = r L/A. Answer A, 1 Ω, is correct.

The specific resistance (r) has units of (ohms•cmil)/ft.

The question gives the wire temperature because resistance increases with temperature in metal. 20°C is standard temperature, and this information assures the temperature is not a factor.

Reference: Thomas A. Hughes, Programmable Controllers, ISA Press, 2001

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
D. 4-20 psig

CCST answer

In standard piping and instrumentation diagrams (P&IDs), instrument signal lines use special markings to indicate whether the signal is pneumatic, electric, hydraulic, or some other type. In this figure, there are two types of instrument signals in use. The double cross-hatched lines denote the pneumatic signals to the steam control valve and the process outlet flow control valve. The dashed line is the electrical control lines between various instruments. In process control applications, pneumatic signals are usually 3 to 15 psi (pounds per square inch gauge pressure), and the electric signals are normally 4 to 20 mA (milliamperes) DC (direct current). The correct answer is A.

nov6

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