How to accurately control flow rates in your microfluidic setup using Bronkhorst® flow sensors ?
How to control the flow rate in your setup with very high accuracy ?
The aim of this application note is to show how to perform easily a very responsive and precise flow rate control anywhere in your setup by using an Elveflow® OB1 pressure & flow controller and a Bonkhorst® 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 if any advice on how to tune the PID parameters is needed go to our dedicated tutorial.
Bronkhorst ® very high precision measurement will enable you to both control the volume of liquid going through your microfluidic chips (as with a syringe pump) and the flow rate very quickly.
Coriolis flow measurement
Using the Coriolis Effect (describing how moving object 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 does not depend on fluid specific heat like Thermal mass flow meters.
Coriolis flow meter can be used with gas and liquids and distinguish themselves by their high accuracy and fast response time.
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Mini Cori-Flow operate 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 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 geometry and the tube material properties but also the mass of the fluid in the vibrating tubes.
Bronkhorst® flow sensor
Adjustable range well adapted for microfluidic application:
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
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 tubing 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 a 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 fix it to a stable surface as often as possible. If you need to measure gas flow rate, see in the datasheet the specific recommendation for the sensor position.
1) First launch the Elvefow® smart interface (ESI)
Click on « Add Instrument »
3) Once both instruments are added you will 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.
9) Example of a triangle PID regulation with a triangle pattern between 50 and 200 µL/min with a 10s period. The flow rate is displayed on the right scale of the graph.
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