In melting furnaces for metals with temperatures above 800°C, temperature measurement is typically done using various manual techniques depending on the phase of the metal (solid, solid + liquid, or liquid). Here are some commonly used methods:
Thermocouples: Thermocouples are widely used temperature sensors for high-temperature applications. They consist of two dissimilar metal wires joined at one end. The junction of the wires is placed in contact with the metal being measured, while the other end is connected to a temperature display or control unit. The temperature is determined by measuring the voltage generated due to the temperature difference between the junction and the reference junction.
Pyrometers: Pyrometers are non-contact temperature measurement devices that detect thermal radiation emitted by the heated metal. Infrared pyrometers, specifically, are commonly used for high-temperature measurements. They measure the intensity of infrared radiation and convert it into temperature readings. Pyrometers are suitable for measuring temperatures of solid or liquid metals from a distance without physical contact.
Optical Methods: For metals in the liquid phase, optical methods can be employed. One such technique is using a sight glass or an observation port to visually inspect the molten metal. Experienced operators can estimate the temperature based on the color, appearance, and behavior of the liquid metal.
Dip or Immersion Probes: In cases where direct contact with the molten metal is feasible, immersion probes can be used. These probes, usually made of ceramic or refractory materials, are immersed into the liquid metal, and their temperature is measured using thermocouples or other temperature sensing elements embedded within the probe. Care must be taken to ensure the probes can withstand the high temperatures without melting or deteriorating.
It's important to note that high-temperature measurements require specialized equipment and safety precautions due to the extreme heat involved. Professional operators with appropriate training and protective gear should handle these measurement techniques to ensure accuracy and personal safety.