Abstract: The thermal time constant of fine metal wire segments, such as those used to initiate explosive reactions, is measured by passing a variable frequency source of current through the wire. The magnitudes of the sine and cosine components of the third harmonic of the voltage developed across the wire are detected and compared to each other to provide a control signal which is applied to the frequency source to change the its frequency in a direction which tends to make those components equal in magnitude. The magnitude of the control signal, when the third harmonic sine and cosine components are equal, is displayed as a function of the thermal time constant of the wire segment.

Abstract: A probe for measuring temperatures in a hot gaseous medium such as the gases inside the shaft of a blast furnace. A first tubular member extends from a base structure such as a blast furnace wall into the gaseous medium. Successively smaller, second and third tubular members are concentrically positioned inside this exterior tubular member. Preferably, an exterior protective member also surrounds the first tubular member. A refractory material is interposed between the exterior protective member and the first tubular member to minimize temperature fluctuations in the body of the probe itself. Thermocouple leads extend longitudinally in an air space between the second and third tubular members and then protrude to the exterior of the probe. A forward fluid coolant passageway is formed inside the third tubular member.