Fast-Response Aircraft Temperature Sensors

Abstract

Three aircraft temperature sensors were compared in clear-air conditions on the NCAR King Air: a standard Rosemount nondeiced, fast-response flight test probe, the NCAR K probe, and a modified Rosemount probe with the platinum wire element replaced with a small thermistor bead. Responses to transient temperature changes were compared from soundings through sharp inversions. High-frequency spectral comparisons were obtained from level runs in the marine boundary layer. All three probes followed a two-time-constant response. The response of the thermistor-modified Rosemount probe was, however, much closer to a one-time-constant model than the two others. Following previous results and analyses, it appears that the longer time constant in the Rosemount probe is largely due to the contact of the platinum wire element, which is wound around mica supports. The long unsupported wire elements in the NCAR K probe do produce a superior high-frequency response, but low-frequency response is anomalous, perhaps due to the large plastic body placed upstream of the wires to separate out particles. The two-time-constant temperature response was compared for the three probes by developing expressions for the time derivative and time integral of the normalized temperature that separated the relative contributions of the sensor element and its support.