TABLE OF CONTENTS M JANSSENS, Southwest Research Institute, USA
Fire testing relies on fundamental measurements of physical quantities such as temperature, pressure, flow rate, mass, etc. This chapter provides an overview of the fundamental measurement techniques that are commonly used in support of flammability testing of materials. Each section begins with a description of the sensors that are used to measure a particular physical quantity. This is followed by a discussion of some of the challenges that need to be overcome to perform accurate measurements. The chapter concludes with a brief introduction to the concepts of measurement error and uncertainty.
Thermocouples are by far the most commonly used sensors to measure temperature in fire tests. A basic thermocouple circuit consists of two wires of dissimilar metals or metal alloys that are joined at one end and left open at the other end (see Fig. 2.1). When the junction is heated, an electromotive force is generated that results in a voltage differential between the open ends. This is referred to as the Seebeck effect. The Seebeck voltage is not affected by the temperature gradient in the wires. Thermocouple wires can be extended with other types of metal wires (e.g., lower grade extension wire) provided that both ends of the thermocouple wires are at the same temperature. Figure 2.2 shows a variation of the basic thermocouple circuit. In this case the voltage differential between the open wire terminals is a function of the temperature...
