Experimental evaluation of differential thermal errors in magnetoelastic stress sensors for Re<180

In this paper we discuss laboratory results from solenoidal magnetoelastic measurements performed on a sample of bridge suspension cable. The experiments were designed to answer basic questions regarding the potential effects of inhomogeneous temperature fields and differential thermal errors between sensor and sample on the accuracy of coercive force measurements. The experiments were conducted with a sample of suspension cable installed in a temperature-controlled thermal chamber. Internal cable temperatures were measured with fine thermocouples which did not breach the sheath, permitting knowledge of the temperature field to be obtained without altering heat transfer. Two sets of experiments were conducted. First, magnetic measurements were taken with the sensor/cable in thermal equilibrium at two different temperatures, and at intermediate points when the temperatures of different ferromagnetic components of the system varied. The magnitude of different heat transfer effects were quantified, and correlated with estimates of the coercive force. Secondly, in order to judge the absolute accuracy of the measurements and to obtain data for further optimizing computer simulations, reference magnetic data was measured using two techniques on a single wire sample of the cable steel. These results are an important step in quantifying the overall accuracy of these sensors.