Campbell Scientific CR200X CR200/CR200X-series Dataloggers - Page 58
SDI-12 Recording, Cabling Effects on Measurements
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Section 4. Sensor Support 4.6 SDI-12 Recording Read More! SDI-12 Sensor Support p. 112 and Serial Input / Output p. 105. SDI-12 is a communications protocol developed to transmit digital data from smart sensors to data acquisition units. It is a simple protocol, requiring only a single communication wire. Typically, the data acquisition unit also supplies power (12V and ground) to the SDI-12 sensor. The CR200(X) is equipped with 1 SDI-12 channel and an SDI12Recorder () CRBASIC instruction. 4.7 Cabling Effects on Measurements Sensor cabling can have significant effects on sensor response and accuracy. This is usually only a concern with sensors acquired from manufacturers other than Campbell Scientific. Campbell Scientific sensors are engineered for optimal performance with factory installed cables. 4.7.1 Analog Sensor Cables Cable length in analog sensors is most likely to affect the signal settling time. For more information, see Signal Settling Time. 4.7.2 Pulse Sensors Because of the long interval between switch closures in tipping bucket rain gages, appreciable capacitance can build up between wires in long cables. A built up charge can cause arcing when the switch closes, shortening switch life. As shown in FIGURE. Current Limiting Resistor in a Rain Gage Circuit (p. 46), a 100 ohm resistor is connected in series at the switch to prevents arcing. This resistor is installed on all rain gages currently sold by Campbell Scientific. Figure 32: Current Limiting Resistor in a Tipping Bucket Rain Gage Circuit 46