Campbell-scientific OBS500 Smart Turbidity Meter with ClearSensor Tech Manuel d'utilisateur télécharger pdf (Page 20)

OBS500 Smart Turbidity Meter with ClearSensor™ Technology

Historically, most turbidity sensor manufacturers and sensor users labeled the

units NTUs, for Nephelometric Turbidity Units. ASTM and the USGS have

come up with the following unit classifications that are applicable to the

OBS500:

Optical Backscatter FBU Formazin Backscatter Unit

Side Scatter FNU Formazin Nephelometric Unit

Ratio Back and Side scatter FNRU

Formazin Nephelometric Ratio Unit

The document “U.S. Geological Survey Implements New Turbidity Data-

Reporting Procedures” details the units:

http://water.usgs.gov/owq/turbidity/TurbidityInfoSheet.pdf

Throughout this manual, the measurements will simply be referred to as

Turbidity Units (TU).

FIGURE 5-1. Drawing of the OBS500 sensor

5.3 Measurement Details

The OBS500 design combines the sensor, analog measurement, and signal

processing within a single housing resulting in the integration of state-of-the-

art sensor and measurement technology. The 24-bit A/D has simultaneous

50/60 Hz rejection and automatic calibration for each measurement. A number

of additional advanced measurement techniques are employed to harness the

best possible performance available from today’s state-of-the-art sensor

technology. The sensor reverts to a low-power sleep state between

measurements. A series of measurements is performed, yielding two turbidity

and one temperature value. This measurement cycle takes about 20 seconds.

The measurement cycle is activated by commands via SDI-12, RS-232

terminal commands, or a control line(s) going high (analog measurements).

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Campbell-scientific OBS500 Smart Turbidity Meter with ClearSensor Tech Manuel d'utilisateur Page 20