November 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

Using Modbus, what is the MAXIMUM level of precision available?

A. 8-bits

B. 16-bits

C. 24-bits

D. 32-bits

CAP answer

The correct answer is B, 16-bits.

Common Modbus uses two 8-bit bytes for each data register.

2 x 8 bits = 16 bits

To achieve more precision special programming or a specialized version of Modus is necessary. Eight bits is less precise than 16-bits; 24-bits and 32-bits require uncommon means to achieve.

Reference: Bella Liptak, Instrument Engineers Handbook, Volume 3 (3rd Edition), Process Software and Digital Networks; ISA, 2002

Modbus transmits over serial lines between devices. The simplest setup would be a single serial cable connecting the serial ports on two devices, a Master and a Slave.

The data transmits as series of ones and zeroes (bits). Each bit is a voltage. Zeroes are positive voltages, and ones are negative voltages. The bits transmit very quickly. A typical transmission speed is 9600 baud (bits per second).

Reference: http://www.simplymodbus.ca

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 most common pressure tap is the:

A.  Corner

B.  Flange

C.  Pipe

D.  Vena contracta

CCST answer

The purpose of pressure taps is prevent gas or vapor accumulations in the connections between the pipe and differential-pressure (dP) measuring device. 

There are five common locations for dP taps. They are flange taps, vena contracta taps, radius taps, full-flow (or pipe taps), and corner taps.

In the U.S., flange taps are the predominant choice for pipe sizes 2 inches (50 mm) and larger.

The best answer is B, flange.

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

Since a single failure can cause or offset multiple portions of a system or machine, analysis must continue until the ___________ is found.

A. Maintenance supervisor

B. Maintenance file

C. P&ID drawing

D. Root cause

CIMM answer

The correct answer is D, root cause.

A single component failure or malfunction will often result in numerous additional shutdowns and/or alarms. This original failure is referred to as the root cause of an event. If an alarm log or history is available on a computer or HMI screen, try scrolling to the very first recorded alarm to determine if that is the one that caused the sequence of errors to occur.

Reference: William L. Mostia, Jr., P.E., Troubleshooting: A Technician's Guide, 2nd Edition, Research Triangle Park, NC, ISA, 2000.

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