Campbell Scientific OBS-5+ Sediment Concentration Monitor and Pressure Sensor - Manual (Page 15)

OBS-5+ System
6. Operation
6.1 Instrument Setup
6.1.1 Mounting Suggestions
Maximum depth for the OBS-5+ is limited by the installed
pressure sensor. If the maximum depths are exceeded,
the pressure sensor will rupture and the housing will flood. CAUTION
The depth limits are listed in TABLE 6-1.
TABLE 6-1. Working and Maximum Depths
Pressure Sensor Working Depth Maximum Depth
5 Bar 0 to 50 meters 75 meters
10 Bar 0 to 100 meters 150 meters
20 Bar 0 to 200 meters 300 meters
(1 Bar = 10 dBar ≅ 10 meters of fresh water)
The following precautions should be followed to ensure the unit can function
properly and is not lost or damaged.
• Always orient the unit so that the OBS-5+ sensor “looks” into water clear
of reflective surfaces.
• Pad the endcaps that contact metal with electrical tape, neoprene, or
expanded polyethylene tubes.
• Never mount the instrument by its endcaps or attach anything to them.
This could a cause a leak.
6.1.2 Surveys
The OBS-5+ will usually be towed with a cable harness for surveys. The serial
cable can tow the OBS-5+ without a depressor weight or vane as long as the
connector is strain relieved. Strain relief can be provided by attaching the
cable to the stainless steel housing (FIGURE 4-1) with a cable grip and a
length of 3 mm (1/8 in) wire rope. Install a cable clamp with a 0.5 m wire rope
to the serial cable, and clamp the wire rope to the pressure housing with two
stainless steel hose clamps, providing a small loop of slack cable to absorb
towing forces. The unit can be powered with an external battery, as shown on
FIGURE 6-1, and the serial output can be transmitted by either RS-232 or
RS-485 protocols. The latter protocol is recommended for cable lengths
greater than 25 m. An RS-485/232 serial converter is provided with each unit.
An RS-232 to USB converter is an available option.
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