Densitometers measure the optical, photographic or area density of a material. They are used in a wide range of applications, from film processing to medical scans. Densitometers are composed of a light source aimed at a photoelectric cell and an analog meter or integrated circuitry to show the data. There are three basic types of densitometers: scanning densitometers, reflection densitometers, and transmission densitometers. A scanning densitometer often has separate, pre-set steps for mid-density (MD) and density difference (MD) measurements. A reflection densitometer measures light reflected back from a surface. A transmission densitometer is used to measure the optical density of transparent materials.
Densitometers measure the value of light absorption in photographic films or printed paper. They are specified for either black and white or color film applications. A reflection density meter can measure the dot area, dot gain, contrast, hue, and grayness in printing applications. An operator can read the material density of the product coming off the press and recalibrate any of the particular ink-supplying units on the press to compensate for errors. A transmission density meter measures the densities of transparent films for photographic, X-ray, and microfilm applications.
Special types of densitometers are also used to measure the density of specific substances or materials. Medical applications for density measurement use dual energy X-ray absorptiometry equipment for bone density scans. A bone density scan is an X-ray machine that measures the bone mineral density of a patient’s bones. These devices are frequently used to screen for and diagnose osteoporosis, a weakening of the bones. Density measuring devices also include nuclear densitometers that are used in materials testing, such as the evaluation of the density of concrete in construction applications or the particulate concentration of slurries in mining applications. Scanning densitometers and spectrophotometers are also used in the printing and graphic arts industries.