New flow controller for low volumes

Burkert's Type 8756 achieves accurate control or measurement, thanks to its Coriolis sensor which is claimed to enhance stability and removes the requirement for zero-point adjustment in changing process conditions. The Type 8756 is aimed at OEM machine builders and system integrators and can control or measure a wide variety of liquids, whether aggressive or neutral, for small quantity applications ranging from chemical injection to food and beverage flavourings. A minimum measurable flow rate of 0.01 kg/h can be set, and go up to a maximum of 25 kg/h with a high measuring range of 1:300. The MFC/M also measures liquid density and temperature. Burkert says that minimal calibration is required when controlling or measuring liquids with different viscosities, saving time in set-up, and that the accuracy of readings is maintained. Liquids with viscosities up to 200 mPas can be measured, or higher on request.

The Type 8756’s Coriolis sensor is stated to provide the highest level of accuracy of flow measurement, achieving +/- 0.2% of the measured value at 0.0014 kg/h. This is combined with high repeatability with +/- 0.1% of the measured value at 0.007 kg/h and a fast measurement response time of <750 ms. Immune to external influences such as vibration, pressure and temperature, and with high zero-point stability, Burkert says that the MFC/M gives reliable measurement to the smallest quantities of liquid. Unlike various alternative measuring principles, the Coriolis sensor does not require a set inlet or outlet section before or after the device to guarantee accuracy. The most significant advantage of the Coriolis measurement principle is that it measures the true mass flow of a liquid and is not influenced by changing temperature or pressure conditions, says the company. In addition to the mass flow rate, the temperature and density of the medium are measured simultaneously. This system also means that the MFC/M is maintenance and wear free. 316L stainless steel construction of the MFC/M body and sensor ensures resistance to corrosive substances.

The Coriolis principle is based on the continuous measurement of the phase shift of tube oscillation caused by the liquid which flows through it. The phase shift is proportional to the mass flow of the medium and is converted into a signal. The system comprises a thin S-shaped measuring tube, which is set in vibration by an external exciter coil. The high frequency measuring tube vibrates freely between two fixed points with the changing vibration, caused by the medium flowing through it, signifying the phase shift. As a mass flow controller, the Type 8756 is designed for dosing of small quantities of typically expensive liquids conveyed from an unpressurised container. High precision dosing is achieved with a micro annular gear pump with a lowest flow rate of 50 µl, which provides extremely low pulsations across a very large control range. The pump is self-priming and is hermetically sealed.

For pharmaceutical applications, the Type 8756 MFC/M achieves FDA – Code of Federal Regulations Title 21 Paragraph 177 (CFR 21 177.2600) and accreditations also include USP Class VI chapter 87 in vitro and 88 in vivo, Implantation and Regulation (EG) No. 1935/2004 about materials and articles intended to come into contact with foodstuffs. Burkert can provide additional accreditations on request. Communication with the process control infrastructure takes place via CANopen or CANopen-based büS as well as an analogue option. Configuration and diagnostics are readily implemented by the Bürkert Communicator software tool, which is available as a free download.