After nearly 15 years in a food-producing factory, control design, for me, has become a streamlined process where the environment is safe and relatively clean. The usual cast of characters, as I call them, are a couple of NEMA 12 enclosures and some combination of a safety circuit, servo or variable-frequency drives, and a programmable logic controller (PLC) or programmable automation controller (PAC) to make it all work together.
I’m not saying that it’s boring or uninspired, as we never really do the same thing twice, but the process from concept to design to execution has the same flavor due to common components. Rarely do we get to step into other production environments, but they sure do offer some challenges not found in a factory that combines dry ingredients to make up some of the common convenience foods found on the shelves of your local food market. Many environments are much more challenging and, in some cases, downright dangerous.
Throughout my career, I have had the opportunity to work in the chemical, petroleum, plastics, water-treatment and mining industries. Each one has its own set of challenges, but the common thread is elements that, given the right situation, can cause an explosion.
Wait, water treatment? Yes, even that environment can be hazardous to the operator. Some applications can be monitored away from the source of danger. For instance, in a steel-processing plant or a water-treatment plant, the operator can monitor and interact with the process from the safety of a control room.
In days of old, such interaction involved physical buttons and lights and gauges to represent the various stages of the operation. In today’s controls environment, we have human-machine interfaces (HMIs) that graphically represent the operation and also provide the buttons and selectors and dials to interact with the process.
In hazardous environments, the operator is at risk because of the process or a by-product of that process. In plastics, for instance, the risk is primarily from the extreme heat required to mold parts and from the noxious gases that are released as a result of melting and combining pellets to make up the composition of the plastic material.
In the petroleum and chemical industries, it is the product itself that presents the risk to the operator. In mining, the environment itself presents the greatest risk to the operator and in the processing of mined materials, the by-products are often a fine dust that is, itself, at risk of explosion, if exposed to a spark.
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This same risk is present in milling operations like the production of fine sugar, corn starch, baking soda and other such ingredients used for baking. One spark in a contained area can cause a flash and resulting explosion.
The primary source of a spark is electronics or open contacts from relays and switches. While we might think that the touchscreen that we use for operator interaction is safe, the actual danger is the smarts behind that screen.
The power supply, the motherboard and other components that turn a program algorithm into the pixels that are displayed on the screen are capable of creating heat and giving off sparks, even on a microscopic level. It is that spark, that catalyst, that can turn fine particles of dust or the vapor from chemical, petroleum or plastics molding into a combustion chamber with enormous risk to life and limb.
So, how do we address the need for safe interaction with the look and feel of operator interfaces? As it turns out, the solution borrows from the control room of the past. If we can separate the smarts, and, thus, the spark-producing devices, from the display screen, the risk to the operator is greatly reduced.
