How to control the flow using an OB1® pressure controller and a flow sensor?

Microfluidic flow control : The OB1® pressure controller has the advantage to be the fastest and the most stable of the microfluidic flow controller. In combination with a flow sensor, it can also perform an ultra-precise flow control and monitor the amount of liquid injected in a chips. You can request a flow rate value in the Elveflow Software and the pressure controller will automatically adjust pressure to reach the requested value thanks to a customizable PID Feedback loop. This application note aims to guide you to easily perform this flow control.

Flow control algorithm

The Elveflow smart interface provides an efficient flow control algorithm that allows to easily put up your experiment. Even if you are not familiar with this kind of algorithm, the interface can set these parameters for you with an auto-tune button. You then only have to adjust a bit the speed and the smoothness of the regulation using the corresponding parameters. These parameters are :

• The PID type : first let it to basic, it’s very efficient in most of the cases
• The “max flow”: change this parameter only if you use only a small portion of the sensor range. Otherwise don’t do anything and let it to zero, it will automatically assume that you are using the whole range.
• The “P” parameter: reduce it if you get instability problems
• The “I” parameter: increase it to have a responsive system, but progressively to stop when instabilities arrived.

Don’t worry! Press the auto-tune button and the software will evaluate your set-up and adjust the “P” and the “I” parameters for you. So first, change nothing and press it, you can then adjust according to your needs.

For this setup, you will need the following Elveflow® devices for the best microfluidic flow control :

• Elveflow® pressure & flow control instrument (OB1)
• Microfluidic Tubing for the fluidic connection of the setup elements
• Microfluidic Fittings & Connectors
• BFS or MFS

The first important things to do when you want to run the auto tune is to have your setup ready: checkup that the connections are well established, the valves in the appropriate configuration and the system ready.

It is also important to be in a steady state, make some liquid circulate into the setup first to avoid transitional states that will give a wrong system calibration.

Then launch the Elveflow® smart interface and follow these steps:

This case is a typical microfluidic cases well adapted to our flow regulation All the regulation parameters where compute using the “auto-tune” functionality. It gives a fast regulation (rise time of 0.2s) with a little bit of overshot and a good stability.

This example shows very fast switches between 60 µL/min and 10 µL/min with 1s time period. In this case, the user needs to adapt a bit manually the parameters given by the auto tune to have a stable system for these very fast transitions and an ideal microfluidic flow control.