Food processing plants are increasingly under scrutiny from government overseers as well as the press concerning safety, security, and food purity. Regulations such as the Food Safety Modernization Act, have focused attention on the prevention of accidental contamination. Measures have also been introduced to protect food from deliberate tampering from criminal or terrorist sources. Physical security and cybersecurity, then, are top of mind in food processing facilities.
Safety Integrity Level (SIL) 3 is becoming increasingly crucial for achieving the required level of safety, particularly in facilities where hazard risk is a factor. A SIL is a measure of safety system performance, or probability of failure. SIL 3 is one of the highest integrity ratings.
When a major U.S. food processor was upgrading a plant, it carefully evaluated several control technologies for its systems. It processes both consumer and industrial products such as pepper, cinnamon, cumin, coriander, anise, celery, kola nuts, ginger, and cloves.
Process engineers were looking to bring about a significant process change to improve yield loss, meet current plant safety standards, streamline operations, and heighten cybersecurity. They performed a task-based risk assessment to characterize the tasks to be completed. Each task was rated on frequency, probability of incident, and severity. That enabled them to determine mitigating actions and isolate the different kinds of safety devices required. This included a PLC to act as the system brain, a safety motor control, an emergency stop pushbutton, a non-contact safety switch, and a locking safety switch.
Plant engineers devised key product selection criteria such as cost, return on investment, ease of maintenance, compactness, and the ability to integrate into the existing infrastructure. Some products failed to measure up against these criteria. For example, a safety relay was missing key capabilities and its lack of scalability meant that multiple devices would be required. A prospective safety controller offered basic logic functions but was more expensive and more difficult to maintain.
The Siemens SIL 3-Rated PLC System for Food Process Plants fit all necessary criteria. It proved to be cost-effective, compact, easy to maintain, and highly scalable. The facility adopted the Siemens S7-1500 in a 200SP form factor. Despite its added functionality, safety, and security, operators are able to troubleshoot this model in the same was as a regular PLC. Further, its remote racks are easily installed.
Similarly, when it came to motor control component selection, several products failed to make the grade. A redundant motor offered low cost and maintainability. But it didn’t scale and took up a large footprint. A safety motor starter fit most criteria except scalability. A Variable Frequency Drive (VFD) candidate wasn’t scalable or compact enough for its intended use.
All components, then, were chosen from the Siemens Safety PLC architecture catalog. The Siemens S7-1500 PLC has ET 200SP modules for scalability. Both local and remote racks can be added rapidly.
Safety features include short circuit detection, cross channel detection, 1-1 verification, 0-1 verification, the ability to drive up to 2A loads, integration of diagnostics to the HMI, IOP diagnostics, ProfiSAFE communication to the PLC, and a ‘Safe Torque Off’ feature via local terminals. The Siemens safety starters also eliminate need for redundant contactors.
The system has been running successfully now for several months.
“The SIL 3-rated Siemens PLC for Food Safety has streamlined our plant operations and boosted productivity,” said the Controls Engineer for the food processing plant. “It has enabled us to maintain safety and security in a cost effective and scalable manner.”Have an Inquiry for Siemens about this article? Click Here >>