A Guide to the Automation Body of Knowledge PDF

Introduction

Good control requires measurements that are accurate, reliable, responsive and maintainable. These factors are influenced by the choice of principle used for the measurement, the detailed specifications and features of the instrument selected and specified, how well the instrument and its installation is maintained, and particularly the installation details.

The vast majority of physical measurements in processes are of the big four: flow, pressure, level, and temperature. This topic will focus on the more popular methods for measuring these variables. Analytical measurements are covered in the next topic. While this topic is titled "process" instrumentation because the larger number of applications are in process and utility applications, much of this instrumentation is used in many other areas of automation application wherever continuous measurements are needed.

Much of the focus in this topic is on compact "transmitters"—devices that combine the sensor and communicating electronics in one package. Some temperature measurements are an exception to this, since those devices often separate the sensor and the communicating electronics. These transmitters sometimes take on different names: level transmitters become level gauges and flow transmitters become flowmeters.