Data logger wiring

Campbell Scientific data loggers typically use SDI-12 to measure the sensor because RS-232 Recommended Standard 232. A loose standard defining how two computing devices can communicate with each other. The implementation of RS-232 in Campbell Scientific dataloggers to computer communications is quite rigid, but transparent to most users. Features in the datalogger that implement RS-232 communication with smart sensors are flexible. communications require more terminals per CS650, and RS-232 programming is more complicated than SDI-12 programming.

Wire color, function, and data logger connection for SDI-12 shows the SDI-12 wiring for the CS650 water content reflectometer. SDI‑12 data is transmitted to a CRBasic data logger odd numbered control or U terminal. Wiring information for RS-232 communications is provided in A200 and Device Configuration Utility.

Wire color, function, and data logger connection for SDI-12
Color	Function	Data logger connection
Green	SDI-12 data	C, SDI-12, or U configured for SDI-12¹
Red	SDI-12 power	12V
Black	SDI-12 reference	G
Clear	Shield	G
Orange	Not used	G
¹U terminals are automatically configured by the measurement instruction.

NOTE:

The orange wire is only used for RS-232 communications and should be grounded when using SDI-12.

For the CR6 and CR1000X data loggers, triggering conflicts may occur when a companion terminal is used for a triggering instruction, such as TimerInput(), PulseCount(), or WaitDigTrig(). For example, if the CS650 is connected to C3 on a CR1000X, C4 cannot be used in the TimerInput(), PulseCount(), or WaitDigTrig() instructions.

FAQ(s)

Can the cable for the CS650 or CS655 be shortened?

Modifications to the CS650 or CS655, including shortening the cable, will void the warranty. However, shortening the cable will not affect the sensor’s performance. If a decision is made to shorten the cable, care should be taken to avoid damaging the cable jacket and exposing bare wire except at the ends that connect to the data logger or multiplexer terminals.

Can the cable length for a CS650 or a CS655 really be up to 2,000 ft?

The cable properties and power requirements of the CS650 and the CS655 are such that communication with a data logger may work for cable lengths greater than 2,000 ft. If multiple sensors are communicating through the same universal or control terminal, the total length of all of those sensors must not exceed 2,000 ft.

In practice, it is less expensive to purchase a new data logger than to buy a CS650 or CS655 with 2,000 ft of cable. If the cable is run through conduit, or if a 2,000 ft long trench needs to be excavated, then the installation cost becomes more expensive than buying another data acquisition system and sensors with shorter cables.

Does the cable for the CS650 or CS655 have to go in conduit?

The cable for the sensors is rugged and resistant to damage from the sun and typical weather conditions. However, it is susceptible to damage from rodents, machinery, shovels, and so forth. Running the cable through electrical conduit or PVC pipe will help protect it, but this is not an absolute requirement. In areas where rodent activity is low, direct burial in a trench is usually sufficient. A particularly vulnerable location is where the buried cables exit the ground and enter the enclosure housing the data logger. At that exit point, take steps to protect the cable from damage.

Can more than 10 CS650 or CS655 sensors be put on the same data logger terminal?

Yes. Because there are a total of 62 available SDI-12 addresses (0 to 9, a to z, A to Z), it would be possible to communicate on the same universal terminal or control port with 62 sensors if each one had a unique address.

In the specifications for the CS650 and the CS655, a limit is stated of 10 sensors per universal terminal or control port because the -VS option gives the sensor an SDI-12 address that matches the last digit of its serial number. That limits the available addresses to 0 to 9, for a total of 10 available addresses. To use addresses a to z or A to Z, change the sensor address with an A200 Sensor to PC Interface or with terminal commands.