To keep the gremlins out of a programmable controller system, avoid those areas where mistakes are most likely to occur. Here are the five most common planning and installation errors that cause poor operation. And, they even occur at companies with the best engineering staffs.
Lack of memory mapping
One of the pitfalls frequently encountered is the failure to plan software programs — through memory mapping — before configuration. Memory mapping establishes the design concept and the method of arranging files. Setting up all programs in a consistent manner achieves the same look and feel, which makes it easier to design and maintain programs.
Memory mapping not only makes writing programs easier, it speeds troubleshooting. For example, a software bug in the interface program for a group of robots can be fixed more quickly if the applicable program is easy to find. It should be located under the same file name in controller No. 1 as in controller No. 10.
Users should establish standard memory- mapping conventions and apply them to all of their systems — even for controllers from different vendors — as consistently as possible.
For example, a maintenance engineer should be able to find the communications interface, message, or diagnostic programs in the same location and under the same file name in any controller, regardless of the controller function. In other words, programs that perform a certain type of function, such as enabling a robot to run or a programmable controller to communicate, should be placed in the same file and location every time, regardless of the machine manufacturer.
Poor grounding of equipment in a manufacturing environment can cause random problems that are difficult to troubleshoot. For example, stations on an improperly grounded system can disappear from the screen of the network manager (person who monitors network functions) and then re-appear.
When application engineers are asked to assist a customer who can’t get a programmable controller running, they start by ensuring good grounding practices. Often, that is all it takes to get the system running. No hardware or software changes are needed.
Making sure that your programmable controller is properly grounded is generally a simple matter of following a few guidelines:
• Use good grounding practices in accordance with the manufacturer’s recommendations and the National Electrical Code (NEC).
• Provide the installer with customer-specific guidelines for installing the equipment.
• Use the correct size ground wire based on the equipment vendor’s specifications and the NEC.
• Attach the ground wire to the correct lugs on the power supply and the controller.
As simple as these guidelines may seem, they ensure that grounding is done properly and save hours of troubleshooting.
Improper network connections
Often, users or vendors fail to make proper cabling and termination connections. Sometimes, very simple things are overlooked. For example, terminating resisters on remote I/O links and communications networks provide proper impedance matching. If a link is not terminated, it can act as an antenna, picking up noise from other devices in the facility. To determine the proper terminating resistance, check the specific controller instruction manual for recommendations.
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Neglecting to support an investment in equipment with a comparable investment in the people who operate and maintain it is a common and costly mistake. These individuals require knowledge in two areas: the controller system and programming techniques.
Knowledge of the system capabilities helps to ensure that the right piece of equipment is applied to the task. It also enables you to realize the full potential of the equipment and maximize the investment.
Sometimes, the system engineer or programmer may lack sufficient training in application or programming techniques that make the system more efficient.
There are a number of sources for training. However, the manufacturer of the programmable controller is probably best qualified to help students learn the fine points of the particular control system.
The training chosen should be performance-based. In the past, training classes tried to cover everything about the controller, whether the student needed to know it or not. Newer methods teach only those aspects of the system that the student will use in day-to-day work. This approach is often faster and more effective. Before implementing such an approach, perform a training needs analysis, in cooperation with the supplier, to assess current skill levels and determine the appropriate training.
Finally, a programmer can’t retain all of the information provided in a course, no matter how good it is. Thus, it is important to provide refresher training that helps students hone their skills and keep up to date on the latest hardware and software enhancements.
Inadequate troubleshooting techniques
When problems occur during an installation, users need to have a well-defined troubleshooting methodology. The ability to systematically locate, identify, and correct problems determines how quickly the system can start running again.
This requires knowledge of problemsolving techniques and the ability to use diagnostic software tools. For this reason, field engineers often take courses in closed-loop, corrective-action methods for systematically identifying, diagnosing, and fixing problems. This training includes root-cause failure analysis, a formal process for locating the source of a problem. Using formal methodology, such as this, ensures that problem fixes are permanent and documented. Without formal troubleshooting techniques, users are more likely to put off problems, or worse, waste time fixing glitches that are only symptomatic of the real problem.
Planning is the key
By applying the three Ps (planning, planning, and planning) of system integration, you can avoid mistakes and shorten the installation time. The key elements in good planning are:
• Documentation. Adequate documentation can eliminate many potential problems. For example, when electricians are forced to guess their way through an installation, it invites wiring problems. Ensuring the availability of good documentation is a small price to pay, considering the risk of damaging the programmable controller when power is applied and delaying machine startup.
• Standards. A well-defined set of standards and specifications should be included in the documentation. This information should include wiring conventions, documentation standards, naming conventions, and drawing standards. Such information helps to ensure (1) that the system meets your needs, and (2) that the equipment is installed properly.
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• Coordination and teamwork. The documentation is an important tool for communication between the different parties involved in the process, such as your maintenance crew and OEM support engineers. Involve the OEM and controls vendor early in the specification process to determine, for example, what features are needed, how the control system should be laid out, and how interfaces will be written.
• Final preparation. To eliminate down-time during a controller installation, insist on as much testing and debugging as possible before the vendor ships the system. The vendor should perform a modular build, simulating the application as closely as possible, and perform operational tests on the system.
To speed the installation, some vendors provide equipment footprints that can be laid out on the shop floor. This enables you to prepare for the installation by bringing power and cabling to the spot. When the system arrives, only final connections are necessary.
Taking these steps in planning a programmable controller installation will greatly increase the chances of setting a realistic schedule and sticking to it. The installation will be much smoother with fewer problems. And, you will start production more quickly.
Support system helps to locate and fix faults
Though several measures can be taken to help prevent common mistakes in programmable controller applications, some faults may still occur. When this happens, the first priority is to quickly get the system running again. A key factor is making sure plant employees are properly trained in troubleshooting and maintenance procedures.
A recent tool used in developing job performance is called an Electronic Performance Support System (EPSS). Unlike traditional computer-based programs, an EPSS is a flexible system that enables people of various skill levels to easily access information, assistance, and training as required by their jobs. The information is available on demand and without the assistance of a trainer.
One such program, developed for programmable controllers, enables plant workers to choose between different modules for fault simulation, troubleshooting, and programming procedures. Then, it guides the user through these procedures by simulating the required steps with detailed, lifelike graphics.
By using such tools, maintenance personnel can more easily identify and correct programmable controller faults before they cost thousands of dollars in downtime.
Glenn MacGeorge is the supervisor of engineering services for Allen-Bradley Co. Inc., Troy, Mich.