High accuracy mass flow controller for gas adds analogue comms

Bürkert has augmented its Type 8742/46 range of mass flow controllers/meters (MFC/M) for gas applications with the addition of analogue communications onboard. 

Characterised by their high measuring accuracy and repeatability, the Type 8742/46 range now also includes an option with PROFIBUS-DP directly integrated.

Available as mass flow controllers or meters, the devices share the same technology while Type 8742 handles low to mid flow, with a nominal range from 0.010 lN/min to 160 lN/min, and Type 8746 is designed for high flow, covering 20 lN/min up to 2500 lN/min. 

The MFC/M is suitable for a range of applications, from metal and glass manufacturing through to filling systems.

To enable economical measurement and control upgrades for plants not using digital communications, the latest release adds analogue communications interfaces including 4-20 mA, 0-20 mA, 0-10 V or 0-5 V. A new PROFIBUS-DP variant has also been released. The two new models join the existing digital communications variant, featuring onboard CANopen or CANopen-based büS, which is able to integrate with all leading Ethernet-based networks and fieldbus. The digital option can support up to 32 MFC/M on one fieldbus gateway.

The success of Bürkert’s Type 8742/46 MFC/M devices is attributed to their accuracy and fast response times, combined with their repeatability and stability of calibration. This is achieved through Bürkert’s MEMS (microelectromechanical systems) technology, enabling the sensor to be positioned directly in the gas flow, where heat dispersal is measured between two resistors.

Since the sensor is mounted in the gas stream, as opposed to a capillary sensor, changes to the flow rate are identified more quickly without a thermal delay.

Together with the direct-acting proportional valve, the process is regulated with high response sensitivity.

The low to mid flow Type 8742 hosts a MEMS sensor mounted directly in the gas flow that is positioned in a bypass channel tube, measuring a sample and providing a faster reaction compared to a capillary sensor. 

Alternately, the high flow Type 8746 measures gas flow in the main channel itself. The advantage of this design for high flow is the ability to maintain pressure, which would be reduced with a bypass capillary channel sensor or other restrictions within the flow. This means that accurate and reliable flow rate detection is achieved, even in low pressure conditions.

The same technology also improves stability of measurement over time as it removes the repeated heating of the tubing usually associated with a conventional MFC, which generates mechanical wear and drift in the measurement reading. 

Instead, with Bürkert’s design placing the sensor within the gas flow itself, measurement stability is retained as the device isn’t subjected to the stresses of repeated heating.

Along with the Bürkert Communicator Software, which enables simple configuration and diagnostics, the optional USB büS stick interfaces between PC and process instrumentation. The büS stick can be used for data transfer and to change settings, for example to carry out an autotune for improved accuracy.

The Type 8742/46 has been designed to operate in more challenging environments and as well as IP65/67 conformance, it also adheres to ATEX II Cat. 3G/D or USP Class VI, FDA, EG 1935.

Image Caption: Bürkert has augmented its Type 8742/46 range of mass flow controllers/meters (MFC/M) for gas applications with the addition of analogue communications onboard.