The common Turbidity Meters use incandescent lamps as light sources, which emit broad spectrum. The wide range of wavelengths can cause colorimetric interference in turbidity readings. Also, incandescent lamp output tends to reduce over time. Due to this frequent replacement of lamp & calibration is required.
Model NT 4000 uses a narrow band monochromatic light source ( I R LED ). It has a long life & very less wavelength interference.
Spectralab Model NT 4000 Turbidity Meter is benchtop turbidity meter and is the most advanced portable microcontroller based Turbidity Meter. It is based on nephelometric and ratiometric principles of turbidity measurement. It uses LED & meets EPA 180.1 and ISO 7027 as well as an infrared ratio ( IR ratio ) mode that gives results in accordance with EPA GLI method 2. It has a memory to store 40 results. The data can be transferred to PC & then printouts can be taken in a document format with report number, data & time.