MICRO DOSING – CREATING AN APPLICATION SPECIFIC SOLUTION
FLUID HANDLING MICRO DOSING
BURKERT
MICRO DOSING – CREATING AN APPLICATION SPECIFIC SOLUTION
Industries that employ micro dosing technology such as pharmaceuticals , medical applications including in-vitro diagnosis , environmental analysis and inkjet printing represent a diverse variety of applications . What is essential for all of them is that the most appropriate design and materials choice can be made for each one .
Tony Brennan , Field Segment Manager Gas & Micro for Bürkert Fluid Control Systems , looks at the technology involved in micro dosing and how the latest developments can be integrated into existing equipment .
The two most common methods of micro dosing are time-pressure dosing and volumetric dosing ; each has its strengths and most appropriate applications so making the right choice is essential to a successful installation .
Control of time and pressure
Creating a micro time-pressure-dosing system requires a range of components that need to be carefully linked together to deliver a reliable and effective solution . The initial starting point is the pressure vessel where the dosing fluid is stored . This needs to be fitted with both level sensors and a highly accurate pressure transducer to ensure a constant supply of fluid at the correct rate .
The fluid is initially controlled by flow control valves which deliver it to the dosing system . In some cases , a conductivity probe can be fitted at this point to check that the correct fluid is being used . The dosing system itself will be based around a precision flow control valve that meets the specifications of the process .
Time-pressure dosing needs two controlled circuits , one to control the dispensing of the fluid and the other to maintain the pressure of the propellant gas that is used to drive the liquid through the system . With a known system pressure , the volume being dispensed is controlled by the defined opening time of the valve . This operation is usually controlled by a PLC via a HMI .
This design has a number of benefits : It is capable of delivering a high dosing frequency as well as controlling the dosing speed . The dosing volume is variable , to the point that continuous dosing is also possible .
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This design is typically compact in dimensions and can be arranged to deliver several different fluids into one process .
Modern valve design has enabled micro precision while at the same time maintaining the highest hygiene standards . Onboard circuit boards enable calibration and process parameters to be retained within the valve assembly while network connectivity is assured through fieldbus communications . This type of system is more commonly seen in pharmaceutical , medical and biotech applications as well as drinks vending machines , where speed and hygiene are prerequisite .
Volumetric dosing
For applications that still require accuracy as well as a high dosing speed , micro dosing pumps provide the answer . These are excellent for continuous dosing applications and their more simplistic arrangement makes them very cost effective . They are often used in process filling , the dosing of adhesives or lubricants as well as environmental analysers .
Again , micro pumps are designed for a variety of applications . Often the dosing amount is controlled by a frequency generator and accuracy levels are typically ± 2 %. In some cases , all the wetted parts can be easily changed , and the fluidic chamber can be designed as a disposable item .
Selecting the most appropriate materials and specifications is best done with assistance from a manufacturer , which has the expertise and application knowledge to create the best solution .
Installed reliability and precision
The whole purpose of micro dosing systems is to deliver repetitive volumes of fluid quickly and accurately . Moreover , the accuracy must not decline over the lifetime of the dosing valve , so continued precision and long-term reliability are essential . To that end , Bürkert has developed a family of microfluidic valves that can operate at high pressures with a typical service life of 200 million cycles .
Within this range there are specialist products , such as the Type 6712 Whisper valve , which offers fast acting control and an internal volume of just 5 μl . Products such as this can be combined with a host of compatible control equipment to create tailor-made systems for a wide variety of applications .
From the initial application assessment , through design and construction to installation and commissioning , working with a single supplier can reduce complexity and deliver the most efficient solution .
Of course , these systems need to fit seamlessly with the existing process equipment , especially in terms of communications . As an expert in fluid control systems , Bürkert offers a complete turnkey solution for all micro-dosing applications , including complete integration with the existing network topology .
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