High precision for time-pressure microlitre dosing

Laboratory equipment and analysis devices used in the life science as well as pharmaceutical sectors require very accurate and repeatable dosing components. Tony Brennan reports

Combined with its existing range of dosing valves and pumps, the Type 8763 controller means that Bürkert can provide a full-service offering for micro volume time-pressure dosing.

Improving laboratory performance

Research companies and laboratories working in sectors such as genomics and in-vitro diagnostics are under pressure to maximise output, but must also maintain accuracy. 

Manufacturers of bench-top equipment for these applications have several choices in terms of the technology they use to measure and dispense fluids.

Syringe dosing offers excellent precision for example, but it is not suitable for high-speed applications, it takes up quite a lot of space and cleaning of the equipment can be difficult.

Some improvements can be achieved through batch dosing – reducing the equipment footprint and increasing speed, but flow rates can be limited, and dosing volumes may only have a certain amount of flexibility. There is also increased complexity in the control valves and dosing reservoir, all of which need to be cleaned between applications.

Time-pressure dosing, on the other hand, offers improved flexibility in dosing quantities, high speed operation and a cost-effective solution for multiple dosing points. It is an important process that is ideally suited to genomics, and processes in the pharmaceutical sector.

Maintaining accuracy

Time pressure dosing uses a pressurised carrier gas to optimise the performance of the dosing valves that dispense micro-volumes of reagents as part of an automated process. This method of liquid measurement provides continuous dosing, saving time compared to refilling a syringe pump. It is also free from downtime or rejects at the beginning of dosing cycles, reducing overall production time and wastage.

However, each time the dosing valves operate, the pressure in the reagent storage vessel drops slightly and, unless this is corrected, the dosing volumes will gradually decrease. It is therefore essential that the supply pressure in the tank is constant and stable.

Improved dosing consistency

Bürkert’s Type 8763 closed-loop controller ensures that stable dosing of microlitre volumes is provided, even with minimal pressure difference between dosing cycles.

Functionality such as an additional pump or pressure sensor can also be added through a further sensor input and actuator output.

High-accuracy repeatable dosing is supported with active pressure relief for precise regulation, while bidirectional control can increase or decrease pressure in the storage vessel. This delivers short response times, which ensure immediate and reliable pressure control.

The Type 8763 is available in three pressure ranges and both analogue and digital variants, with the latter also incorporating analogue control. Digital communication achieves optimum process parameters by running defined pressure cycles to specific programs, which can be set according to application requirements.

Pre-developed, bespoke programs with features including pressure curves and warning thresholds can also be developed by Bürkert on request.

Robust materials

In addition to accuracy and consistency, Bürkert has also paid close attention to the materials that are used throughout its products.

As an experienced supplier to many industry sectors that handle aggressive liquids, as well as needing to meet stringent hygiene standards, Bürkert uses a range of materials to match the chemical resistance requirements of the application.

The latest development by Bürkert can be combined with a range of dosing valves, all designed with media separated actuators constructed using the most appropriate materials. This also extends to the Type 8763, where the pressure inlet is only exposed to air or inert gases. However, the vent port may be in direct contact with solvents and so can be specified from a list of materials including PPS and FFKM.

Flexible communications

Instruments used in laboratory applications need to record data and be capable of sharing information with a wider network.

The digital interface of the Type 8763 also enables parameters to be changed while the system is running for improved control flexibility.

Automated process documentation increases process safety and access to data is also possible during system operation.

The digital variant of the Type 8763 pressure controller communicates over Bürkert Systembus (büS), based on the CANopen protocol with additional functions.

The pressure controller joins Bürkert’s Efficient Device Integration Platform (EDIP), which enables intelligent networking down to sensor and actuator level over büS connectivity.

Industrial communication standards including PROFINET, PROFIbus, Ethernet and Modbus/TCP are supported to enable flexible integration of system components.

The pressure controller is simple and quick to set up with plug-and-play functionality and no calibration required. Configuration, parameter setting and diagnostic management takes place with Bürkert’s free-of-charge Type 8920 Communicator software.

Downloadable from the Bürkert website, the Communicator software provides an intuitive, standardised interface for büS-compatible components.

Bürkert’s Type 8763 Pressure Controller offers millisecond response times and active pressure relief to maintain optimum performance and continuous dosing.

Together with a range of dosing valves, manifolds and integrated controls, Bürkert can work with OEMs to create an initial concept and develop it to a bespoke solution. This approach reduces development time and minimises the time taken to bring new equipment to market.

Tony Brennan is Field Segment Manager, gas & micro, Bürkert Fluid Control Systems.