7.3. Ocean Controls Modbus/BACnet interfaces

*This topic is primarily for information only. These Ocean Controls (OC) products have good reliability and rarely need troubleshooting provided the instructions and information in their product manuals has been read and understood. In the rare circumstance where a fault with one of these products is suspected then it is usually best to contact Ocean Controls Support by email – typically only OC will have the technical knowledge to diagnose potential faults with these products.

The Australian company Ocean Controls markets a range of add-on devices that can interface Davis Vue and VP2 stations to industrial systems of various types using either the Modbus or BACnet interface protocols. The devices may seem complex because of all the acronyms flying around, but are actually relatively straightforward to set up and to use.

Use of such devices is associated with an array of acronyms such as PLC (Programmable Logic Controller), RTU (Remote Terminal Unit), BMS (Building Management System) and SCADA (Supervisory Control And Data Automation) but all of these tend to refer to different aspects of controlling machinery and processes in an industrial setting. For example, a typical use for such devices is to control building heating and ventilation systems dependent on outside weather conditions (sensed for example by a VP2 station). Because they provide an interface from Vue and VP2 stations, these OC products are widely sold by Davis resellers worldwide.

Modbus and BACnet are two alternative standards for providing a data interface between controllers and machinery. Their purpose is to provide a common interface standard to allow equipment from different manufacturers to be interconnected reliably. There are many pros and cons to each standard (see www.wevolver.com/article/bacnet-vs-modbus for more details) but in essence Modbus is a simpler but less secure option, while BACnet is more secure and technically more comprehensive.

Another important aspect of usage is the communications protocol that the devices are designed for. Modbus commonly uses either RTU (Remote Terminal Unit) which equates to communication over RS232 or RS485 serial lines or, alternatively, TCP/IP Ethernet. BACnet MS/TP uses Master-Slave/Token-Passing over RS485 serial protocol.

There are several products in the OC range which differ in the exact functionality offered, but share some common features:

• Require an external voltage supply of 12v or 24v DC, but PoE (Power over Ethernet) variants are also available for some models.
• Need an RS232 data input from the weather station. This means that the VP2 data must be supplied from a legacy console type paired with a Weatherlink serial logger. The only legacy console now available new are the cabled and wireless Envoy products. Note that the newer 6313 Weatherlink console and 6100 Weatherlink Live products are NOT compatible with these OC interface products.
• Different units provide Modbus or BACnet compatibility and other hardware variations.
  

GWY-141 Modbus interface (now discontinued)

TBA

KTA-282 Modbus interface (now discontinued)

TBA

KTA-302 BACnet interface (now discontinued)

TBA

KTA-382 Modbus interface (launch March 2025)

TBA

KTA-402 BACnet interface (launch February 2025)

TBA

To be completed!

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