Microfluidics application note
Published on 28 August 2019
How to accurately control flow rates in your microfluidic setup with very high accuracy?
The aim of this application note is to show how to easily perform a very responsive and precise flow rate control anywhere in your setup, by using an Elveflow® OB1 pressure & flow controller and a Bronkhorst® Coriolis flow sensor.
Our user-friendly software includes a PID algorithm perfectly suited to the OB1 pressure & flow controller.
For further information about the PID algorithm or for any advice on how to tune the PID parameters, go to our dedicated tutorial.
The Bronkhorst ® Coriolisvery high precision measurement will let you both control the volume of liquid going through your microfluidic chips (like with a syringe pump) and the flow rate very quickly.
Coriolis flow measurement
Using the Coriolis Effect (describing how moving objects deflect from a straight path when viewed from a rotating frame) on a fluid going through a vibrating tube, it is possible to derive the mass flow through the tube, and also the density of the fluid at secondary output. This direct measurement is very accurate because there is no need to correct it with temperature, pressure and density and it does not depend on fluid-specific heat like Thermal mass flow meters. The Coriolis flow meter can be used with gas and liquids and distinguishes itself by its high accuracy and fast response time.
Coriolis flow sensor principle
Mini Cori-Flow operates according to the Coriolis principle. The instrument can be used to simultaneously measure the mass flow, temperature and density. When a fluid flows through a vibrating tube, Coriolis forces are generated, which bend or twist the tube. The extremely small tube displacements are detected by optimally positioned sensors and evaluated electronically. Since the measured phase’s shift of the sensor signals is proportional to the mass flow, the mini Cori-Flow measures the mass flow directly. The measurement principle is independent of the density, temperature, viscosity, pressure, heat-capacity or conductivity. The tubes always vibrate at their natural frequency, which is a function not only of the tube’s geometry and the tube’s material properties but also of the mass of the fluid in the vibrating tubes.
Wide range, well-adapted for microfluidic applications:
SETUP
For this setup, you will need the following Elveflow® devices:
- Elveflow® pressure & flow control instrument (OB1)
- Microfluidic Tubing for the fluidic connection of the setup elements
- Microfluidic Fittings & Connectors
- Bronkhorst flow sensor
Components list
[ob1f_rebound]
Setup Diagram
Step by step control with Elveflow® smart software
This section explains step by step how to perform the flow rate control.
Make sure that all the cables and tubings are well connected to your Elveflow® instruments (USB cable, 24V DC, Flow sensor data cable, etc). Perform leakage tests and remove any air bubbles before starting your experiment.
Knowing what fitting is best suited to your needs is the first step towards success. If you’re not familiar with microfluidic fittings, you may read our specific tutorials.
The flow sensor is very sensitive to vibrations and movement perturbations so it is recommended to affix it to a stable surface as often as possible. If you need to measure gas flow rate, see in the datasheet the specific recommendations for the sensor’s position.
1) First launch the Elvefow® smart interface (ESI)
Click on « Add Instrument »
2) Add both your OB1 ® with its specific settings and your Bronkhorst ® flow sensor (Cori-Flow)
3) Once both instruments are added you will see the above window.
5) Open the configuration window of the BFS Flow Sensor and select the “Connected to” tab. Click on the “Edit Sensor visualized in” button to open the channel selection window. Add the channel of the OB1 that will be used for feedback control.
6) You are now ready to begin the flow control!
Open the OB1 window. You should see your flow sensor on the channel selected in the previous step.
7) Change the control mode to “sensor” and open the Channel setting window and go to the “Feedback” tab to tune the parameters to match your requirements.
8) You can now perform your regulation. Set a flow rate and change the profile of the regulation according to your needs.
Open a graph to follow the evolution of the flow rate.
In this example, the regulation was on a constant flow rate of 120µL/min.
Microfluidics knowledge
Do you want tips on how to best set up your microfluidic experiment? Do you need inspiration or a different angle to take on your specific problem? Well, we probably have an application note just for you, feel free to check them out!
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