FLOW-BUS, Fieldbus Communication Protocol

FLOW-BUS is a RS485-based field bus communication system for parameter value exchange between digital Bronkhorst products. In this system, each device features a microcontroller for its own tasks but also for exchanging parameter value information with other instruments / devices on the same FLOW-BUS system.

FLOW-BUS systems may have a minimum of 2 and a maximum of 126 connections. The maximum length for datelines between the first and the last connection may be up to approx. 600 meters. Longer distances are possible, but only in combination with special bus-repeater modules. Each instrument connection T-part (stub) must be kept as short as possible (maximum cable length 0.5 meter).

• FLOW-BUS is a multi-master network with a token-ring architecture
• Baud rates of 187,500 (default) or 400,000 Baud
• 15-24 Vdc supply voltage
• easy installation and communication with other Bronkhorst equipment
• automatic node search
• automatic bus optimization (gap fixing)
• PC-communication through RS232 via local-host function (recommended number of instruments is 10) or stand-alone interface
• optional: galvanic isolation up to 500 V (for data lines)
• connection to a maximum of 120 instruments to 1 bus
• max. bus length: 600 meters

FLOW-BUS, Fieldbus Communication Protocol

Since 2000, Bronkhorst has been developing digital instrumentation according to the “multibus” principle. The basic pc-board on the instrument contains all of the general functions necessary for measurement and control, including alarm, totalizing, and diagnostic functions. Its standard features include analog I/O-signals and also an RS232 connection. Additionally, these instruments can integrate an interface board with DeviceNet, PROFIBUS DP, Modbus, FLOW-BUS, or EtherCAT protocol.

The first generation (MBC-I) resembles a 16 bit Fujitsu controller. In 2003, the Multibus type 2 (MBC-II) release replaces the first generation. This version also relies on the 16 bit Fujitsu controller but with several improvements to the MBC-I. One of them is the current steering of the valve. Additionally, it reduces heat production and improves control characteristics.

The latest version Multibus controller type 3 (MBC3) was introduced in 2011. It is built around a 72MHz 32 bit NXP ARM controller. It has AD and DA controllers on board which makes it possible to measure noise free and control valves without delays. The internal control loop runs 6 times faster than the MBC-II, therefore offering an improvement in control stability. It also has several advance functions like reverse voltage protection, in-rush current limitation, and over-voltage protection.