For many years, Campbell Scientific has carried the OBS-3 and OBS-3+ sensors from D&A Instrument Company. These sensors monitor turbidity and suspended-sediment concentrations using optical backscatter (OBS) technology.

Campbell Scientific recently purchased D&A Instrument Company and their OBS product line. Production and business operations have been moved to our headquarters in Logan, Utah, and we are now responsible for all warranty repairs, quotes, orders, and any other business regarding D&A Instrument products.

The OBS technology works by emitting a near-infrared light into the water, then measuring the light that bounces back from the suspended particles.

We’ve already begun production of the OBS-3+ probe, and the OBS-3A and OBS-5+ water-quality systems. These later two systems provide data logging capability, store up to 200,000 lines of data, and include PC software for system setup and data retrieval.

Each OBS-3A has a turbidity sensor and a temperature sensor. A pressure transducer for depth measurement and a conductivity probe are available as options. The system can perform wave processing of the depth measurements using a fast Fourier transform (FFT) algorithm for wave height and period.

The OBS-5+ monitors high suspended sediment concentrations and depth. Its unique optical design consists of one emitter and two detectors. This design allows the OBS-5+ to sense suspended sediment concentrations for up to 50 g/l in mud or 200 g/l in sand. A pressure transducer is included for depth measurements.

Campbell Scientific will carry on the tradition of high-quality craftsmanship that D&A established. We will continue to seek product advancements, at times consulting with John Downing, the former president of D&A.


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