Improve Industrial Temperature Measurement Precision for Cost-Effective Energy Usage

Abstract

Temperature measurement and energy efficiencies have always been tightly interrelated. Recent years have seen substantial advancements in the ability to make industrial temperature measurements with absolute accuracy. This capability should continue to have a great impact on industrial energy efficiency. "Absolute Accuracy" is a new concept in industrial temperature measurement. Making a measurement with "Absolute Accuracy" has enormous advantages in major industrial processes from heat-transfer to combustion thermal efficiency. Absolute measurement accuracy is especially critical when one temperature measurement is to be compared to another temperature measurement or if the measurement is to be used as part of a calculation formula such as BTU usage or compensated flow. The thermocouple and the RTD sensor continue to be the workhorse sensors for industrial measurements, but the precision measurement capability of the RTD sensor is showing real value in new installations. For temperature measurements under 1,000°F, the RTD is extremely stable and repeatable in almost all measurement conditions. There have been significant advances in the ability to accurately read these sensors, particularly in industrial applications where the temperature sensor is installed in a remote location. Four-wire sensor measurement techniques can now be used for reading RTD's in industrial applications. These four-wire measurement techniques have improved the practical measurement accuracy in industrial applications to better than ±0.1°C. This is at least ten times better than any practical industrial temperature measurement accuracy made prior to 1980. These significant accuracy improvements have been matched by similar improvements in measurement stability, particularly from smart temperature transmitters. Measurement accuracy and stability improvements have allowed for similar advances in process control strategies and in precision energy use studies. Until recently, the inaccuracy of process temperature measurements have stymied implementation of sophisticated control algorithms. With the advent of precise, stable temperature measurements, a number of process control strategies can be implemented using real-time enthalpy balances for control of batch and continuous reactions. These control strategies can result in very significant improvements in both throughput and quality. Similar improvements can be made where it is important to compare an industrial temperature measurements. These comparisons are frequent in energy use studies to identify and isolate potential energy savings. This article examines the advances in remote temperature measurement techniques for the process and utility industries. It offers several examples of the significance of the on-line control techniques.