Hardware design best practices are not static

May 17, 2016 2:47:25 PM | Posted by David Paul

Hardware design changes might not occur as frequently as software updates, but they need to be reevaluated to ensure they still represent best practices based on the latest hardware versions and application instructions from the manufacturer.

People in the automation industry understand that the pace of change and improvement on the software side of the business is relentless. The fact that the latest version of software issued yesterday may be obsolete in a week is just the nature of the industry. What many engineers and designers fail to recognize is that hardware design best practices also change, although at a slower pace than software.

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Control System Engineering: Are PE stamped designs a requirement?

Mar 4, 2015 9:16:00 AM | Posted by David Paul

Professional engineering licensure for control system designers, engineers, and integrators is always a topic that can bring forth heated arguments both for and against licensure. The purpose of this article is to put forth the facts and let the readers determine if professional engineer (PE) designed control systems are a requirement for their systems and facilities.

Professional engineering licensure for control system designers, engineers, and integrators is always a topic that can bring forth heated arguments both for and against licensure. The purpose of this article is to put forth the facts and let the readers determine if professional engineer (PE) designed control systems are a requirement for their systems and facilities.

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Identifying power quality issues

Oct 8, 2014 10:38:00 AM | Posted by David Paul

Is your automation problem really a power quality problem in disguise?

Do you have production losses or shutdowns in your plant attributed to the automation system? Do you have automation problems attributed to software “bugs” and other software anomalies that happen at random? Does your automation system experience excessive or high rates of hardware failure in components such as PLCs, power supplies, variable frequency drives, and communication devices? Many facilities attribute these costly failures and production losses to either poor vendor hardware and/or poor software programming practices. Many plants simply write off these excessive costs “as a cost of doing business,” and just continue to replace failed hardware and reset the software. These issues should not be accepted.

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Understanding time current curves: Part 3

Feb 13, 2014 8:53:28 AM | Posted by David Paul

The final installment of a three-part series about time current curves (TCCs) reviews the coordination of sample curves and the importance of coordination.

Continued from Part 2

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Understanding time current curves: Part 2

Jan 30, 2014 3:17:29 AM | Posted by David Paul

The second installment of a three-part series about time current curves (TCCs) covers short and long time settings, including their purpose and examples of such overcurrents.

Continued from Part 1

The light blue curve represents the circuit breaker settings for the feeder circuit breaker. The lower portion of the curve (below 0.05 sec or three cycles on the time axis) is the instantaneous trip function. The purpose of the instantaneous trip is to trip the circuit breaker quickly with no intentional delay (no more than a few cycles) on high magnitude fault currents. This quick trip protects electrical distribution equipment from damage and keeps arc flash hazard categories low. Clearly these type faults must be interrupted quickly and do not allow the system to wait and see if the fault will self clear. The minimum instantaneous setting determines the minimum trip setting for the circuit breaker. In the case shown in Part 1, the instantaneous setting is 2,400 A and the maximum value displayed is available fault current at the circuit breaker. Small changes in the instantaneous setting can result in significant changes in the Arc Flash Hazard category, so this is a setting which must be carefully selected according to sound engineering principles.

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Understanding time current curves: Part 1

Jan 28, 2014 8:36:30 AM | Posted by David Paul

The first installment of a three-part series about time current curves (TCCs) provides a quick overview of item identification and how to read TCC plots.

A time current curve (TCC) plots the interrupting time of an overcurrent device based on a given current level. These curves are provided by the manufacturers of electrical overcurrent interrupting devices, such as fuses and circuit breakers. These curves are part of the product acceptance testing required by Underwriters Laboratories (UL) and other rating agencies. The shape of the curves is dictated by both the physical construction of the device as well as the settings selected in the case of adjustable circuit breakers. The time current curves of a device are important for engineers to understand because they graphically show the response of the device to various levels overcurrent. The curves allow the power systems engineer to graphically represent the selective coordination of overcurrent devices in an electrical system. Modern power system design software packages, such as EasyPower, SKM Power Tools, and Etap, contain graphical libraries of curves to allow the power system engineer the ability to plot, analyze, and print the curves with minimal effort compared to the previous methods used when coordinating a power system.

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