Tech Tips February-March 2006


March 28, 2006


How to define standards for HMI screen design

Take into account operators' physical environments, such as control room lighting, how many screens they monitor, and how close they sit to the screens. These factors help determine standards, such as font sizes, symbols, and colors. A shape (or picture) library will help ensure consistency in the desired images. Consider these tips:

  • Make wise use of colors: Make primary data ( process values ) stand out with high contrast. Secondary or support data ( text descriptors ) should be smaller and/or blended with the background. Alarm data must be easily recognizable with bright colors. Dedicated colors should be chosen for each alarm priority.

  • Make sure that process lines flow left to right. Avoid line bends and crossings when possible.

  • Be consistent: Maintain absolute consistency in detail, layout, symbols, and abbreviations.

  • Indicate major process flows with wider lines (from feed to principal products). This approach helps differentiate between major product/process flows and utility lines.

Also find further guidance on HMI screen design from Honeywell in the source below.

Source: Control Engineering November 2005, Back to Basics, ' Four steps to HMI screen design .'

March 21, 2006


5 reasons to isolate I/O signals even without ground-loop problems

Many believe that if there are no ground loops present, there's no need to isolate analog I/O signals. Five common challenges beyond ground-loop nightmares present ample reasons to isolate every analog signal, according to Dataforth Corp.

Reasons to isolate analog I/O signals are:

1. Signal crosstalk;
2. Common-mode voltages;
3. DC common-mode rejection;
4. AC common-mode rejection; and
5. Over-range and input protection issues.

Use of isolated signal conditioners can resolve each problem, Dataforth says, including three-way isolation to eliminate cross-talk difficulties, continuous overload protection, reverse polarity protection, and ANSI/IEEE C37.90.1 transient protection. The company offers an application note called ' Why Isolate ' (Application Note AN116), with more details about recognizing these problems and how isolated signal conditioners can help.

Source: Control Engineering March 2, 2006 Weekly News

March 14, 2006


How lighting techniques enhance vision systems

Lighting techniques (types of lighting and angles) can determine what features on a part stand out, when viewed by a vision system. Ambient lighting on a part can differ dramatically from other options. Some possibilities include:

  • Ring light that surrounds the sensor lens hides raised features;

  • Low-angle light accentuates rough areas and raised edges. It hides shiny areas;

  • Dome light evenly lights the whole part;

  • Backlight shows only the outline;

  • On-axis light can reveal a fingerprint; and

  • Area light at 30 degrees can highlight a raised area and reduce glare.

For more information and illustration of these techniques, visit:

Source: Control Engineering November 2005, ' Get the picture ' sidebar in cover story 'High Horsepower Vision Sensors.'

March 7, 2006


Securing network security—Part 2

Basic guidance about industrial network security appeared in last week's Tip of the Week. A 'to-do' list to lock-in security follows here:

  • Think of the network as a whole and sketch it out-literally.

  • Inventory what the network is connected to-Internet? Wireless?

  • Check for existing security features and make sure they're enabled.

  • Install router switch/firewall between plant-floor network and other networks.

  • Enable router's broadcast storm control capability.

  • Use virtual local area networks (VLANs) to block unauthorized messages between ports.

  • Overlap two VLANs to allow specific data sharing.

  • Use additional dedicated router to allow only authorized traffic between two networks.

  • Test personal computers and laptops that plug into plant-floor network.
    Source: Control Engineering October 2004, Back to Basics on ' Securing network security .'

February 28, 2006


Securing network security—Part 1

The following provides some basic guidance on industrial network security. It focuses on three elements: routers, virtual area networks, and connected PCs.

The most important tool for increasing network security is to locate a router/firewall between local networks and larger systems, especially those tied to the Internet. While switches operate at the data link layer (layer 2), routers generally operate at the network layer (layer 3) with most routers handling TCP/IP messages. A router/firewall matches private Internet addresses with data requests, allowing through only specified messages. Very few unauthorized messages get through routers.

Some users implement virtual local area networks (VLANs) between their plant-floor networks and office systems. Located in the switches' hardware, VLANs block unauthorized messages between network ports.

On the infrastructure side, network managers also must be careful about what devices may be consuming available bandwidth on the plant-floor. Ethernet switches are designed to be very inviting, and someone plugging into an available RJ-45 port can potentially hinder or damage manufacturing processes with unauthorized or untested network traffic.

Caution is further advised about the protocols residing on PCs and laptops that may connect to switches on the plant-floor network. Managers can test new software or devices by running a plant-floor network in safe mode or by setting up small test networks.

A 'to-do' list to lock-in network security follows in next week's 'Tip of the Week.'

Source: Control Engineering October 2004, Back to Basics on ' Securing network security .'

February 21, 2006


Understanding SPC terms

Statistical process control/statistical quality control (SPC/SQC) software, once used exclusively offline for analysis, now integrates with control and human-machine interface software. By working online, SPC/SQC can identify and fix problems before an operator is aware any problem exists.
While using current SPC/SQC software requires less specialized knowledge than previous versions, here are some traditional SPC/SQC terms that might help:

Cp —Process capability calculated by the relation Tolerance/(6 sigma). Cp only measures data dispersion.

Cpk —Process capability calculated by the smaller of (Mean-Upper Spec)/(3 sigma) or (Mean-Lower Spec)/(3 sigma). It measures both dispersion and central tendency of data. A typical 6 sigma program implies a Cpk value of 2 or greater.

EWMA chart —Exponential Weighted Moving Average is a tool used to detect small, recent process variations by assigning an exponentially declining weight to data points as they age.

Pareto chart —A way of classifying problems from important few to trivially many. Defects are assigned a cause and categories ranked in order of number. The most significant problem will be charted the first.

Run rules —Guidelines to detect nonrandom process shifts. Some rules use six or nine data points on one side of the mean in a row. They are based on the likelihood that so many successive readings will not occur randomly.

X bar, R —This most popular of Shewart charts plots average (X bar) and range (R) for a sample.

Source: Control Engineering, April 2000, ' Understanding SPC terms ' sidebar in article 'SPC/SQC Closes the Loop.'

February 14, 2006


Factors for an ergonomically correct HMI

Ergonomic correctness typically is not the first thing on an engineer's mind when working with computer terminals for human-machine interface (HMI). However, not paying attention to ergonomic principles can lead to expensive workplace consequences, including eyestrain, carpal tunnel syndrome, tendonitis, and more.

Ergonomics plays a role in every HMI application, influencing how effectively an operator can use the product. Moreover, ergonomic hazards may be governed by state- and/or federal-government regulations. Also, workplace-related ergonomic injuries may be the source of costly worker compensation claims and lost work time.

Consider the following ergonomic factors when selecting and designing any HMI system:

  • Evaluate an HMI product's ergonomic characteristics along with its functional features before making a selection. Is the screen glare resistant? Is it easy to operate? Is it ergonomically friendly?

  • Exercise the same cautions and restraints when using an HMI product as with any computer activity. Minimize repetitive motion. Be open to modifications to accommodate individual needs.

  • Take time to understand ergonomic concepts and principles when installing any new system. Working smart ergonomically increases workplace efficiency and reduces lost time injuries and worker compensation claims.

Source: Control Engineering, April 2004 Back to Basics, ' Is your HMI ergonomically correct? '

February 7, 2006


How to extract value from historian software

Historian software helps collect and analyze data to improve manufacturing processes and decision-making. That capability can help reshape the future of a business, but requires a firm understanding of capabilities and potential. One process manufacturing company relates experiences to improve its business by incorporating historian software to track past business trends, as well as bring manufacturing intelligence into the process of improving safety and product quality, while reducing production costs.

However, common hurdles are often encountered when extracting value from information-based projects. Here are some problem areas to look for:

  • Isolating and quantifying specific financial benefits;

  • Inconsistent tag naming;

  • Inconsistent instrumentation and data available from plant to plant;

  • Limited application development expertise: Those needing data don't know how to get it; and those with access to data don't know who needs it. Ability to convert raw process data to meaningful and readily usable information is where actual value of a process data historian resides, and few make the most of its available potential;

  • Data integrity: Making sure that data are accurate and consistently recorded; and

  • Data traceability: Making sure that raw data used today to make a decision is also available for future reference and use.

Source: Control Engineering, September 2004, ' Extract value from projects ' sidebar, in Inside Control article 'Process Data Historian Improves Business.'

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