The CAN* peripheral interface (CPI) is a new proprietary measurement bus that provides communication between Campbell Scientific dataloggers and various peripheral modules and sensors. The CPI bus is an improvement upon the SDM (synchronous device for measurement) bus that has served our dataloggers for many years. The CPI bus allows multiple CPI-enabled devices to be connected and controlled through a single port on the datalogger, and synchronizes the measurements of these modules to the scan of the datalogger. The devices and the datalogger operate in concert with one another as a single measurement unit, expanding the functionality of the datalogger.

CPI improvements over SDM include higher data throughput and more robust signaling, allowing much longer cable lengths and immunity to noise. The SDM bus will continue to be supported by the dataloggers, but the CPI bus will be included more and more frequently as a communication option along with SDM as new products are developed.

One motivation for developing the CPI was to provide a solution for the communication and synchronization needs of a new line of datalogger peripherals known as Campbell distributed modules (CDMs). The first two of these modules were released last year: the CDM-VW300 and CDM-VW305 dynamic vibrating-wire analyzers. Other measurement modules are in development. All CDM devices share a common mechanical design that is optimized for building networks of multiple devices. CDM devices enable the customization of a datalogger system by adding unique functions and additional measurement channels as needed, and they provide the flexibility to spatially distribute the measurements.

Campbell smart sensors that have historically used SDM to communicate with the datalogger can also benefit from the CPI bus. We will incorporate CPI into new versions of some sensors to help with their communication and synchronization requirements.

An important design objective of the CPI bus is versatility and ease of use. Connections are made using standard Ethernet cables. CPI-enabled devices offer dual connections to the bus on each unit, making it simple to connect devices in series. Branching network configurations can be achieved using a passive RJ45 hub. Hardware setup is simple, and the CRBasic program disseminates configuration information to the devices at startup. A rich set of bus diagnostic information is available through the datalogger.

The SC-CPI interface module provides a CPI bus connection for our existing CR3000, CR1000, and CR800 dataloggers. The new CR6 is the first Campbell datalogger to directly support the CPI bus. With the future release of more CDMs and other devices that make use of the CPI bus, we will continue to expand the capability of our dataloggers and provide users with the flexibility and configurability they need.

* Controller area network