Turbidity instruments measure the average volume of light scattering over a defined angular range. Both particle size and the concentration of suspended solids, as well as the level of dissolved solids can affect the reading. Turbidity is defined as an expression of the optical property that causes light to be scattered and absorbed, rather than transmitted, in straight lines through the sample. Simply stated, turbidity is the measure of relative sample clarity.
Turbidity instruments can measure not only turbidity but also suspended solids. Turbidity is measured in Nephelometric Turbidity Units or NTU, which represents the average volume scattering over a defined angular range. Both particle size and concentration of suspended solids as well as dissolved solids can affect this reading. When measuring suspended solids, the instruments measure concentration, often in parts per million.
Mounting options for turbidity instruments are quite varied. They can be handheld meters, larger portable meters with wheels or handles for carrying, and modular for interfacing with sensors of different input ranges. Other styles commonly available are specially designed for lab or benchtop use and others for field or in-situ applications. Some of these meters are designed to be mounted in a panel.
Displays for the instruments can be analog meters, a numeric or alphanumeric digital display or video, CRT or LCD. Another option is to have no local display at all and have the data gathered by another instrument. Likewise, the user controls can also be analog or digital or can be operated through a host computer. To simplify the instruments, preprogrammed devices without user controls are available.
Electrical Output Options
Electrical output options are the standard voltage and current outputs as well as an analog frequency or a change in state of switches or an alarm. Serial and parallel interfaces can help connect these instruments to a host computer.
Some features available for many turbidity instruments include battery power for greater portability and built-in signal processing filters. Built-in calibration ability and self-test functions are also available, as are event triggering and ratings for extreme environments. These instruments can also have some controller functionality such as set limits, regulator, or P/PI/PID control.
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