Series A15/76 Turbidity Monitor
from Analytical Technology

Turbidity is a general indicator of the optical clarity of water and is defined as the amount of light scattered from particles in solution. In practice, a light beam is directed into a water sample and a photo detector measures the light scattered at 90° to the incident light beam. While other scatter angles are possible, the 90° measurement angle has become the standard for turbidity measurement in most water systems. It is used as a relative indicator of the amount of suspended solids in solution and is measured in virtually all drinking water systems. It is also used in industrial water treatment systems as an indicator of product water quality.

ATI's Model A15/79 Turbidity Monitor is designed to meet the needs of both municipal drinking water systems and industrial water treatment for reliable, low range turbidity measurement. Using an infrared light source and a 90° scatter measurement, the system provides high sensitivity measurement with unmatched zero stability. Turbidity measurements down to 0.001 NTU or as high as 4000 NTU can be measured with the same monitor, eliminating the need for separate high and low range instruments.

The turbidity sensor used in the A15/76 is a planer sensor with the light source and photo detector mounted on a flat face. Lenses in front of the light source direct the beam of light at a 45° angle into the sample. Another lens in front of the photodetector collects the 90° scattered light and directs it to the detector. The signal generated by the detector is amplified inside the sensor for transmission to the display unit. Periodic pulsing of the light source allows the sensor zero to be adjusted automatically for improved stability in low range applications.

Turbidity sensors are available for measurement in a pressurized flowcell or for direct submersion in open tanks. A 1 1/2" flow T assembly is also available for direct in line measurements. The flowcell is required for very low measurements (0-4 NTU), while the submersion unit may be used for higher turbidity applications such as wastewater effluent or raw water.

Air bubbles are a common problem in many turbidity systems. ATI's turbidity sensor is designed to operate under pressure to eliminate the sample degassing that often causes air bubble errors. Sample pressure in not dropped until the sample exits the measuring chamber, resulting in more reliable measurements. The turbidity electronics unit is a compact panel mount instrument providing an LCD display of turbidity value, as well as indication of alarm status and instrument diagnostics. For stand alone applications, a NEMA 4X wall mount enclosure is available.

The monitor provides display of turbidity over a variety of operating ranges. The minimum display range of 0-4 NTU provides resolution down to 0.001 NTU and is suitable for almost any final filter monitoring application. Range of 0-40 or 0-400 NTU are available for raw water or clarifier effluent monitoring. A0-4000 NTU range may be used for very high turbidity applications such as river water monitoring. In addition, the monitor may be calibrated for suspended solids measurements, with range from 0-10 mg/l up to 0-10,000 ml/l.

Standard turbidity systems provide a variety of outputs. Two programmable alarms with SPDT alarm relays are included, as well as an isolated 4-20 mA output. The analog output may be programmed for full scale outputs as low as 0-0.2 NTU and can inverted if desired. Alarm and output information can be displayed on the LCD at the push of a button and the alarm relays can be activated manually for test purposes when needed.

A15/76 monitors also provide sensor diagnostic functions to warn of conditions that cause inaccurate or invalid readings. The sensor is continuously monitored for optical fouling and will display an alarm message when the sensor requires cleaning. In addition, the sensor will detect the lack of water in the flowcell and provide a "dry cell" when an air interface is detected. These alarm conditions will cause a third alarm relay to activate, which can be used to indicate these conditions remotely.

Because turbidity measurement is often required in wastewater effluents and other applications where sensor fouling can be a major problem, ATI offers a special turbidity unit, the D15/76 system, that uses an "air blast" sensor cleaning system that automatically cleans the sensor as often as necessary to maintain reliable measurements. This system is used only for submersion applications only, and all air supply components required for the cleaning process are supplied in the NEMA 4X monitor package.

Call AFC for details on the NEMA 4X enclosures.

Download a copy of the A15/76 Turbidity monitor literature

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AFC International, Inc.
PO Box 894, DeMotte, IN 46310
715 SW Almond St, Ste C, DeMotte, IN 46310
800-952-3293 219-987-6825 Fax 219-987-6826
eMail: sales@afcintl.com

Last Revised: 1/23/07