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