ENGINEER'S PERSPECTIVE:<br>The Limitations of Instruments
Today’s instruments have become so powerful that the demand for skilled laborers has decreased, and the operators—or tenders—no longer need to have a fundamental knowledge of the materials they are measuring or the manufacturing processes they are controlling in order to perform their jobs. As a result, companies can operate with fewer personnel and lower personnel costs. We have improved production efficiencies and corporate bottom lines—but at what cost?
The Extinction of KnowledgeThe cost has been the extinction of the old timers with the calibrated eyeballs—the guys who could look down the length of a kiln and instinctively tell whether the temperature of the hot zone was correct. Or the maintenance guy who could tell you the carbon content of a piece of steel by the spark pattern when the steel was kissed against the bench grinder. Or the pit foreman who could tell you the alumina content of the fireclay by rubbing his pocketknife against a rock.
In that respect, the ceramic industry is not unique. For example, today’s cash registers contain micro-processing chips that can automatically calculate how much change to return to the customer, enabling retail merchants to hire less skilled, and therefore lower paid, employees to collect their money. The result has been an improved bottom line for the merchant—but also a potential inconvenience for the customer. Have you ever bought something for $19.91, given the employee a $20, then handed him a penny after he had already punched $20.00 into the cash register? The result is the all too familiar “deer-in-the-headlights” syndrome.
What happens in the plant when the product comes out of the kiln over-fired? All the monitors and instruments are indicating normal operating conditions, and we all know that nothing has changed in any of the upstream manufacturing processes. We automatically assume that the raw material supplier is shipping “out of spec” material. But if we still had that old timer around, he would look down the tunnel kiln and mutter something. He would slowly walk to the hot zone, pull out the control thermocouple, slide a new one back in, then slowly walk back to the break room. Several hours later, the plant manager and sleepy raw material salesman would be staring at parts coming out of the kiln that were back in spec and not over-fired.
Getting Back to BasicsThere is no turning back on the use of today’s powerful instruments, and the knowledgeable old timers are no longer around to bail us out. Instead, we must learn how to understand the underlying principles of instrument operation and how the instruments interact with the materials they are measuring and the processes they are monitoring and controlling.
For example, thermocouples age and their output slowly deteriorates. In one plant, a platinum control thermocouple continued to generate an output, but with a lower-than-normal signal. The controller interpreted that signal as a lower temperature and sent a corresponding signal to the kiln to increase power to the hot zone. Over time, the hot zone got increasingly hotter, even though the expensive, sophisticated control instrument indicated that the hot zone temperature was correct.
In a recent “Kiln Connection” column (CI, November 2002), Ralph Ruark warned us to “always question the data.” This is very sage advice. In the example above, no one became concerned about the slowly increasing monthly gas consumption. And worse, no one suspected that the drift in the density or shrinkage values on the SPC charts was significant. Rather than double-checking the kiln’s accuracy by running a set of pyrometric cones through it, the plant personnel simply assumed that the control thermocouple was correct.
We must not be lulled into a false sense of security by believing that instruments are infallible. No matter how sophisticated our instruments become, we should always question the data and have a fundamental knowledge of how those instruments work to ensure that our plants continue to operate as efficiently as possible.