How Did My Cheese Move?

How Did My Cheese Move?

Automation for Quality and Consistency Automation can bring many benefits to an operating environment. Siemens combined various systems and technologies into an integrated command and control system can help improve quality, consistency, throughput and process analysis. Often, an automated system can also lower labor costs and help reduce unscheduled downtime.

In one major cheese manufacturing plant, which had been originally designed with an earlier form of integrated system, the application of automation dramatically updated the original system design, making it more flexible at a relatively modest cost. A very large plant that produces 120 million pounds of cheese each year has increased its yield to even higher levels. By use of smart, standardized PLCs and streamlined graphical software for operations, maintenance and modification, the plant – already sophisticated and fully integrated – increased its Grade A yield to over 97 percent, and upped total annual cheese output by at least ten million pounds. By taking more than 2,500 machines in the cheese plant that had been operating independently, and integrating them into a single continuous system, the cheese makers are now operating at a level of precision largely unknown in the dairy industry. Several years of planning, and a relatively modest investment has allowed plant operators to ramp up to a production increase of “best of fair cheese” every day.

In addition to the obvious benefits of increased Grade A cheese production, the flexibility to continuously fine tune was appealing. Secondary advantages have included reduced maintenance and repair, longer life of equipment, and less waste treatment through recovery of rinses. The $2 million system incorporates smart programmable logic controllers (PLCs), advanced graphical software and a real-time Ethernet data highway to improve operating consistency and minimize spills and waste. Other improvements include reduced maintenance and repair and longer equipment life.

Cheese making is both an art and a science. As a result, it is possible to automate the process. All of the key factors – yield, quality, and flexibility – only result from the tighter control and trending tools made possible from new, integrated systems. Any variation in a batch process like cheese making is hard to pinpoint without them. The cheese vat operation illustrates the superiority of the new control system. Once the vat is filled and the exact quantity of milk is known, the computer calculates the precise amount of starter and rennet required, and adds them automatically at the set time in the process.

The issue of ratios of additives illustrates the difference between the old and the new. Ratios are always based on the exact amount of fill. Prior to installing Simatic PLCs, the Company never achieved exactly 45,000 lbs. at a time, but always aimed for that mark. Once the PLC was in place, all additives could be instantly recalculated and increased by measures of parts per million. The cheese making process begins by adding color, or a “rennet” starter bacteria (a dry powdered solution mixed in-house) into the vats. Bacteria cultures are produced to develop specific strains of starter, the secret recipe; pH controls are still manual. After transferring the milk from the outside storage silos into the plant, eleven vats are filled at 15-minute intervals, followed by the addition of salt.

With automation, the plant successfully operates the vats with an average of only two people. At all critical stages including vats, curd handling, whey handling, starter handling and CIP (clean in place), the PLC is the driver and the back up. In each of these areas the PLC is considered a true confidence builder, checking key measures continuously as each event occurs. Valves and other mechanical devices are looked to for feedback. Confirmation from each device is essential. Record keeping is another important asset. It can archive up to 10,000 messages being monitored and reported to the system. These messages can be retrieved at any of the control stations. As part of the overall PCS concept, PLCs are networked through the 10 Mbaud standard Ethernet bus conforming to IEEE 802.3, which forms the lifeline throughout the plant. This bus ensures manufacturer neutrality, when it comes to interfacing other devices, providing true open architecture. A standardized Profibus fieldbus is used to connect peripheral devices to the PLCs. The process is broken down into a series of islands or cells assigned to PLCs, which handle both fast binary processing (interlocks, sequential controls) and loop controls, such as level temperature, flow and more, with one common configuring technique. Serial buses transfer data to and from the actual process or field. Intelligent, remote I/O are distributed throughout the process, providing significant savings for cabling, also allowing fast start-up and troubleshooting. The individual PLCs, or process cells, are then networked through the Ethernet bus so that all plant areas can be accessed using a single window approach. Transparent to the machine-level area is the logic behind the system, generated through PLCs. This ties in with other graphic-based software, which utilizes blocks to configure the total process. These are standard functional blocks used routinely by control engineers. With a library of 250 functions, these building blocks are used for processing binary, word and real data as well as sequential controls. Configuring is achieved by selecting, positioning and connecting modules on project sheets that are stored in the computer in a layered fashion. To aid configuration, commissioning and later revisions, the control engineer is able to simulate the results of programming for debugging prior to actual downloading to the process itself.

The system even generates its own hard copy documentation using the stored project sheets. With easy to use and understand graphics, operators can be trained in just a few days. Each tank, pump, valve and other piece of equipment is shown on the flow diagram for that part of the process. Each function is shown by a change of color. For example, when a pump starts, the symbol turns green. Fault conditions cause the item to change to red. Labor saving is another benefit. Each step of the process can be tracked from the screen on the platform or from anywhere else in the plant, and if something goes wrong it is displayed immediately. Any deviation in the process will cause an alarm condition or action alert. The configuring software links directly with the PLCs, which in turn are receiving sensory information from the process. To minimize wiring and facilitate future expansion and modification, the system has distributed I/O for its PLCs from one end of the process to the other using the Profibus I/O. These talk over a twisted pair cable to the main PLCs. A major benefit of the new computer system is its troubleshooting capability. A diagnostic system integrated into each PLC tells the operator why an expected response has not occurred after a specific action. For example, why a motor didn’t start when it was supposed to. A display is automatically generated to show the cause, together with date, time and symbolic designators or tags in the PLC program. The actual diagnosis is executed using a personal computer (PC) that’s connected to the individual PLC through the Ethernet bus. This PC contains the diagnostic system program and, when a fault condition occurs, the user program is analyzed backwards until the cause or causes are found. The graphics display indicates pertinent data to either eliminate or minimize unscheduled downtime. Trending capability is another feature. The operator can build trend pictures of whatever information and time period he wants. He can scroll forward or backward in time, and is only limited by the memory of the PC. Today’s automation is flexible, scalable and, in most cases, totally upgradable. Modular components allow precision in configuration, so that the solutions are unique and adaptable to changes in your operations. Explore the possibilities for yourself and you may find automation to be the key to your future success.

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