HMI workstations at a chemical plant

Flat-panel displays, protected properly, can perform well and stand up to hard use even in a hazardous and corrosive environment.

10/31/2011


Using a pressurized enclosure allows a variety of electrical products to be used in a hazardous environment. A slow flow of compressed air drives out potentially explosive gasses. Source: Pepperl+Fuchs, Inc.When Paul Anderson, the electrical controls and instrumentation technician at Hydrite Chemical Company, needed to replace his obsolete control system and field-mounted HMIs, he had a list of plant requirements and regulations that he was determined to meet. He needed an open system for flexibility and easy updates in the future. The operator interface had to be state-of-the-art and extremely rugged, able to withstand the rigors of a hazardous and corrosive chemical plant environment and have a long MTBF (mean time between failure). Plus he wanted a supplier that shared his operating philosophy and would form a partnership to help Hydrite make the best products at the lowest possible cost.

Many industrial plants are still using legacy CRT displays, but many are nearing their end of life and are no longer available. Industrial flat-panel monitors have become the product of choice for such applications but the exact meaning of “industrial” in this context is still not always clear. Due diligence requires customers to investigate who will provide the best industrially hardened or, if required, hazardous location certified LCD flat-panel technology.

Hydrite Chemical Co. is a manufacturer and distributor of ingredients for food and beverage processors, fluoride for water treatment facilities, and a host of chemicals for cleaning and sanitation across a wide range of industries. Hydrite also partners with other companies to prepare high-quality products and distribute them worldwide.

Some of the final products are flammable or have flammable ingredients, so many of the materials and processes used by Hydrite are located in hazardous areas and must meet stringent safety requirements. Most of Hydrite’s Cottage Grove, WI, plant is classified as Class I, Division 1. Other areas in the plant are Class I, Division 2.  Any equipment used must conform to these hazardous area classifications. Hydrite plants are also certified to ISO 9001:2000 standards, which ensures that the products they produce are of uniformly high quality, and that all personnel and processes follow the same formulas and procedures every time.

Flat-panel monitors, even when mounted in a pressurized enclosure, can be very compact, using space efficiently. Source: Pepperl+Fuchs, Inc.Chemicals are produced in batches, and the batch is managed by a combination of automatic control and operator adjustments. Typically, there are multiple feed tanks, with raw ingredients being supplied from drums, totes, and bulk tanks. Correct ratios and feeding of ingredients must be carefully controlled following the recipe’s instructions. Once a batch process begins, time to a completed product can take just a few hours or up to several days. Once the process has started, any interruptions or downtime can ruin the batch. The process also produces emissions and other waste by-products that must be managed, so the ease of operator access is an integral part of the batch processing workflow.

Gaining access to batching and process information directly from the plant floor saves time and can prevent process errors that interrupt production. But having an HMI display close to the process would mean having a Class I, Division 2, industrial-rated monitor designed for continuous use over an extended period of time under heavy-duty conditions. It would have to be located in the manual addition area to facilitate the operators, and include a hardened touchscreen that would stand up to that environment.

Choosing the right system

Anderson was assigned the task of upgrading the aging DCS. First, he selected a state-of-the-art control system with intrinsically safe remote I/O. The benefits of remote I/O were twofold: First, conduit and wiring were significantly reduced along with installation time. Second, the segmented system provided reliable system availability together with the ability to make repairs without shutting down the process.

This photo illustrates the difference between the new HMI approach and the older explosion-proof enclosures used before. Source: Pepperl+Fuchs, Inc.

For the operator interface, he selected industrial workstations with touchscreens from a supplier that designed and built its own products, to Hydrite's specifications, in its panel shop with UL508A, UL698A, and CSA approval.

Anderson chose operator workstations from Pepperl+Fuchs because they met all of his requirements. This came after searching many vendors without success. The units he chose tolerate the harsh manufacturing environment, are resistant to corrosion, and have a MTBF of 500,000 hours. He noted that most other units he considered could only claim half that figure. This meant that his operators could trust that the HMIs would be reliable and redundant within the control system.

Membrane keyboards can also be practical in difficult environments. These are particularly useful where operators are required to input complex or large amounts of information manually, beyond what is practical for a touchscreen. Source: Pepperl+Fuchs, Inc.

The workstations are mounted in a 316 stainless steel NEMA 4X Division 2 enclosure with either a pedestal-mounted or wall-mounted configuration. The enclosure dimensions are smaller than the older explosion-proof units so they take up less valuable space in the facility. With the hardened resistive touchscreens and industrial-grade electronics, the displays on the hazardous factory floor were able to reproduce the same high-quality picture as the monitors in the control room without reprogramming the configuration. Now operators had the same functionality in the plant as they had in the control room. Plant personnel were no longer required to make several trips from the plant floor to the control room each day. It is easier for operators to make changes and adjustments, and they have more meaningful information at their fingertips. This helps avoid unnecessary downtime, and Anderson cites lower maintenance costs. There is also an unexpected bonus: The flat-panel displays consume less power and generate less heat than the CRT predecessors.

The right type of HMI hardware, when used with an up-to-date control platform and well-designed graphics, can create a powerful visualization, control, or information computing solution.

Joseph A. Kaulfersch is a market analyst for Pepperl+Fuchs, Inc.



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