FEATURE FLOW & LEVEL CONTROL MICRO-DOSING:
repetitive reliability I
ndustries 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. 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. The initial starting point is the pressure vessel where the dosing fluid is stored. This needs to be fitted with both level sensors and an accurate pressure
Tony Brennan, field segment manager Gas & Micro for Bürkert Fluid Control Systems, looks at micro dosing technology and shows how the latest developments can be integrated into existing equipment
variable, to the point that continuous dosing is also possible. This design is typically compact 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 high 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 pre-requisite.
VOLUMETRIC DOSING For applications that still require accuracy as well as a high dosing speed, micro dosing pumps provide the answer. These suit continuous dosing
‘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’
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
12 MAY 2018 | PROCESS & CONTROL
applications and their more simplistic arrangement makes them cost-effective. They are often used in process filling,
Modern valve design has enabled micro precision while at the same time maintaining high hygiene standards
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 compatible control equipment to create tailor-made systems for a wide variety of applications. From the initial application assessment,
Bürkert has developed a family of microfluidic valves that can operate at high pressures with a typical service life of 200 million cycles
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. Bürkert can offer a complete turnkey solution for all micro- dosing applications, including complete integration with the existing network topology.
Bürkert Fluid Control Systems T: 01285 648720
www.burkert.co.uk
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56
