February 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 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 II

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

CAP question

To MINIMIZE the effect of feed upsets to the top of a distillation column, the flow feed forward signal should be connected to a tray temperature controller output that then directly manipulates a(n):

A. Overhead pressure controller

B. Linear reflux valve

C. Reflux controller

D. Reboiler stream ratio controller

CAP answer

The correct answer is C, reflux controller.

A distillation tower has feed upsets that are measured and used to create a feed forward signal. A reflux flow controller remote set point becomes the feed multiplied by a reflux-to-feed ratio that the temperature controller output will correct. This is the most linear and accurate way of maintaining the material balance as long as the flow measurements are above their low range ability limit.

Reference: Blevins, McMillan, Wojsznis, and Brown; Advanced Control Unleashed: Plant Performance Management for Optimum Benefit; ISA Press, 2003

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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

One of the most important considerations of the installation of an electromagnetic flowmeter is:

A. The Reynolds Number of the fluid

B. The use of a straightening vane

C. Bonding the flowmeter to the piping

D. Observing the correct polarity

CCST answer

The concept of a magnetic flowmeter is that when a conductor (the fluid in the pipe) moves through a magnetic field, a voltage is produced in the conductor that is relative to the speed of the conductor and the magnetic field.

It is imperative for the electric circuit to be complete to be able to measure the voltage, which is proportional to the speed. Knowing and multiplying the speed of the fluid by the cross sectional area of the pipe gives the volumetric flow rate.

The best answer here is "bonding the flowmeter to the piping," answer C. If the bond between the meter and the piping is not good, the electricity will not flow and the measurement cannot happen.