I am trying to wire three generic rain gauges to a single CR1000 data logger as part of a research experiment. The three rain gauges have a two-pin connector, so the wiring between the gauges and the logger is established with tow-wire cables. Following the example provided by ShortCut, i can wire two of the rain gauges to pulse ports P1 and P2, respectively. However, it is not clear how can I wire the third rain gauge to the data logger. According to ShortCut, i need a three-wire cable -i.e. one to 5V excitation, one to control port C1, and one to ground, Yet, the rain gauge has only two wires; i guess pulse (5V) and gorund. Any ideas on how could i wire this third gauge? can i wire more than one rain gauge to a single pulse port? Any help regarding this issue will be very much appreciated.
Many thanks in anticipation.
The third wire (clear) that you see in ShortCut is the shield connection of the cable. The two conductors you have would correspond to white and black.
Campbell Scientific wires a resistor inside rain gages that allows wiring them the way ShortCut displays. Page 10 of the manual for the TE525 shows the resistor in the circuit. You should not directly connect a rain gage to 5V, unless there is a resistor in it to limit current through the switch. The resistor to add would be 100 Ohms, and does not need to be high precision.
An alternate means of wiring is shown in Table 93 of the CR1000 manual.
JFYI - the two wires from your raingauge are connected to a switch that closes when the 'bucket' tips to the other side.
Also for your problem of having 3 gauges.. see 'Pulse Input on Digital I/O Channels C1-C8' which for my version of the CR1000 manual (Rev 9/09) is under 4.5.2 on page 75.
As for protecting the reed switch contact from current surges over long cables the resitor is very good advice. :-)