Determination of time constants of cold wires

Abstract

The time constant of a fine cold wire used as a resistance thermometer can be obtained by a technique which is based on ideas developed for the pulsed‐wire technique for velocity measurement in highly turbulent flows and in regions of flow reversal. The cold wire is placed downstream of, and at right angles to, a wire of larger diameter which is pulsed with a short duration voltage pulse. The response of the cold wire to the change in the temperature of the flow is used to determine the time constant of the wire, once the pulsed wire time constant is known. Frequency responses based on measured time constants for cold wires of 2.5, 1.3, and 0.63 μm diameters are presented as a function of flow velocity.