What is the difference between halogen and infrared moisture measuring instruments?
Thermogravimetric moisture testers efficiently dry samples by transferring energy by radiation (through waves (energy in the form of waves or particles passing through the medium (in this case the sample)) and convection (heat transfer through mass movement). In contrast, conventional drying ovens primarily use convection to dry samples. Both metal and halogen heating elements radiate energy in the infrared spectrum. (Both are used in the OHAUS MB series.)
Infrared (IR) radiation is part of the electromagnetic spectrum, between microwave energy and visible light. IR consists of thermal radiation with a wavelength frequency range of 0.75 microns (the long wavelength limit of visible red light) to 1.5 microns (the boundary on microwaves). Infrared energy is not visible to the human eye. The red light normally associated with infrared heating is actually reflected red light from the visible spectrum.
Some moisture analysers use a metal heating element, which is simply a low resistance sheet of metal that converts electricity to heat. Such heaters are well suited for environments where glass components are prohibited due to regulatory or safety concerns (e.g., food processing). Metal heaters are not satisfactory because they are very hot and take much longer to heat up than halogen heaters, making them difficult to control and not providing good reproducibility in moisture analysers.
Halogen emitters contain a tungsten heating element in a compact glass tube which is filled with halogen gas to preserve the tungsten element. Halogen emitters emit infrared radiation in the short wavelength range of 0.75-1.5 microns. The compact nature of the halogen emitter improves the heating/cooling response time, shortening the time it takes for the heating unit to reach its full heating power, and ultimately shortening the time it takes to complete the drying of the sample. It also allows for better control during the heating process.
