Campbell Scientific OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors - Manual (Page 20)

OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors
7.2 Mounting Considerations
Schemes for mounting the OBS-3+ and OBS300 will vary with applications;
however, the same basic precautions should be followed to ensure the unit is
able to make a good measurement and that it is not lost or damaged.
7.2.1 Siting
The most important general precaution is to orient the unit so that the sensor
looks into clear water without reflective surfaces. This includes any object
such as a mounting structure, a streambed, or sidewalls. The sensor can see to
a distance of about 50 cm (20 in) in very clean water at angles ranging from
125° to 170°. The OBS-3+ sensor point perpendicular to the sensor body
whereas the OBS300 sensor is orientated to point out the end (see FIGURE
5-1).
The sensor has ambient-light rejection features, but it is still best to orient it
away from the influence of direct sunlight. Shading may be required in some
installations to totally protect from sunlight interference.
7.2.2 Mounting Options
7.2.2.1 PVC Pipe
Mounting the sensor inside the end of a PVC pipe is a convenient way to
provide structure and protection for deployments. The OBS-3+/OBS300 will
fit inside a 1.25-in. schedule 40 PVC pipe.
7.2.2.2 Cable Ties or Hose Clamps
The OBS-3+/OBS300 can be mounted to a frame or post using large, high-
strength nylon cable ties (7.6 mm (0.3 in) width) or stainless steel hose clamps.
When using clamps, do the following:
1. Cover the area(s) to be clamped with tape or 2 mm (1/16 in) neoprene
sheet.
2. Clamp the unit to the mounting frame or wire using the padded area.
Spacer blocks may be necessary to prevent the unit from chafing with
the frame or wire.
Do not tighten the hose clamps more than is necessary to
produce a firm grip. Overtightening may damage the
pressure housing causing leakage.
7.3 Wiring to Datalogger
TABLE 7-1 and FIGURE 7-1 show the recommended wiring configuration for
connecting the OBS sensor to a Campbell Scientific datalogger; wiring to
dataloggers manufactured by other companies is similar. In this configuration,
single-ended analog inputs are used to measure the OBS sensors’ voltage
signal. The red power wire is connected to a switched 12 V channel, which
allows the OBS sensor to be turned off when it is not making measurements.
This reduces current consumption. Dataloggers that do not have a switched
12 V channel can use a relay to turn the OBS sensor off and on. Appendix D,
Datalogger Connection to a Relay, provides information about using a relay.
CAUTION
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