In late 2007 Campbell Scientific, represented by Campbell Scientific Aust , have purchased D&A Instruments and now produce their existing OBS sensors. Since then Campbell Scientific have also released three new sensors.
The major part of the OBS units is an Optical BackScatter sensor for measuring turbidity and suspended solid concentrations by detecting near infrared radiation scattered from the suspended particles. Due to the small size and sample volume, the linear response and wide dynamic range, the insensitivity to bubbles and organic matter as well as rejecting the effects of ambient light and temperature change.
As was the case with the OBS3PLUS, the OBS3+ is still a sensor only device with a high and low output voltage range, but the second voltage output channel of the OBS3+ is now calibrated when the sensor is ordered as a 4-20mA version. When this output option is selected, the channel with the 4-20mA output measures the lower turbidity range and the channel with the 0 to 5V output measures the upper turbidity range. A titanium body option is available which allows the sensor to be submerged in both fresh and salt water to a maximum depth of 1500 metres.
Also submersible, the OBS3A and OBS5+ have built-in batteries and dataloggers, making them stand alone measurement systems that can be used in either fresh or saltwater environments. The OBS3A combines the measurement of turbidity with temperature, depth and conductivity for the ability to get a comprehensive picture of the water quality on site. For highly turbid environments, the OBS5+ uses multiple detectors and an embedded controller.
Combined with a sediment calibration, the measurement method of the OBS5+ allows for suspended solid concentration (SSC) values greater than the normal peaks in response, extending the measuring ranges to 50,000 mg/l (mud) or 200,000 mg/l (sand), depending on the size of the particles. Other innovative options of the OBS3A and the OBS5+ include the possible usage of lithium batteries instead of Alkaline batteries and optional extended pressure ranges.