INTRODUCTION

Despite many advances in electronics and computer technologies, industrial process measurements are still made largely by conventional sensors, such as thermocouples, resistance temperature detectors (RTDs), and pressure and differential pressure sensors that were designed more than 50 years ago. Today, there are smart sensors, fiber optic sensors, ultrasonic sensors, and wireless sensors on the market, contributing significantly to recent advances in instrumentation. Yet many of these new sensors still depend on conventional sensing technologies to measure a process parameter. For example, smart temperature sensors often use RTDs or thermocouples to measure temperature, and smart pressure sensors use conventional capacitance sensing cells, bellows, and other traditional sensors to measure pressure. The smart components are mostly in the sensor electronics and memory and in the sensor's ability to adjust its output remotely using digital technology.

The same is true for wireless sensors. They usually use a conventional sensing device to measure a process parameter and wireless technology to transmit the information to a remote location. Therefore, many of today's instrumentation or sensor problems are similar to those familiar to industry over the years. For example, sensor drift is almost as much of a problem today as it was three decades ago. There is no new sensor technology on the horizon to make possible any significantly new drift-free, sturdy sensors that can readily tolerate the temperature, humidity, and vibration environments that exist in industrial processes. Great advances have been made in producing essentially drift-free electronics for sensors, but the sensors themselves have not changed much over the years. Also, questions still linger over how to objectively assess the accuracy, response time, residual life, and other characteristics of installed instrumentation. No consensus has been established in these areas even among professionals in the process instrumentation field. This book is intended to provide readers with an understanding of some of these problems and to offer practical means to identify them, assess their consequences, and help resolve them.