Campbell Scientific CR200/CR200X-series Dataloggers - Manual (Page 58)

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