The complete instrument engineer knows that behind the glitter of digital control technology lies another world of mechanical field instrument devices from which process control was born. Digital electronics may dutifully perform in a "0" or "1" state, but the artful precision and imaginative designs of analog mechanical field instruments are marvels that often go unnoticed by new generations of control professionals. 

This month's feature article on level switches reminded me of the mechanical heritage of control instrumentation. Take time to examine the torque arm mechanism of a float-type level switch, or the air flow manipulation inside a pneumatic relay. The wizardry engineered into such "low level" mechanical instruments is truly a work of art requiring imaginative application of mechanical principles. What's more, the usefulness of many types of mechanical field instruments transcends the digital era with little danger of being displaced. 

Recently, I witnessed a demonstration of an in-line mechanical flow controller. No microprocessor. No power supply. No digital readout. With the adjustment of a rotary setpoint dial, the device was able to steadily maintain a given flow rate with 0.5% accuracy regardless of upstream pressure surges or temperature variations. What struck me at the moment was that this mechanical flow rate controller design has been around for 40 years. The manufacturer is reintroducing the flow rate controller because of a resurgence of interest within the process industries. Its design, based on principles of fluid mechanics, is catching the eye of process control professionals who are gaining new respect for design simplicity. 

Working with the technology available to them at the time, the forefathers of modern instrumentation crafted mechanical designs in the tradition of old-world clockmakers. Today, the process industries routinely rely on a multiplicity of time-proven mechanical instrument designs for on-line operations. That some early instrument operating methodologies have endured into the 1990s is a tribute to the ingenuity of those designs. 

The electronic and computer orientation of today's young instrument engineers risks misapplication and improper specification of mechanical instrumentation. Greater appreciation for ageless mechanical field instruments is needed. It's refreshing to know that some of man's more skillful instrument design endeavors have survived the onslaught of the chip.