Campbell Scientific OBS300 OBS-3+ and OBS300 Suspended Solids and Turbidity Mo - Page 20
Mounting Considerations, Wiring to Datalogger
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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, highstrength 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. CAUTION 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. 10