They'll perform another blow if the bath is too cool. Operators use oxygen thermocouples in most heats. This includes aluminum grades, for which the carbon levels are very high and the oxygen is very low anyway. At Bethlehem Steel, operators drop thermocouple bombs from above the vessel. The thermocouple is composed of two metals that emit different voltages as they become hot.
Operators infer the temperature from the voltages.
Bethlehem measures oxygen levels by inserting a probe into the bath at turndown. The probe also takes the bath's temperature. It takes 3-3.5 minutes to prepare the test and obtain the results on the screen in the pulpit. In the lab, a robot arm takes a sample to a grinding belt that prepares the surface. The sample then is cleaned and put into a spectrometer, where two or three burns are taken.