Bidirectional Microfluidic Flow Sensor

Electrically charged fluids can’t be used with Flow unit + (M+ and L+) but standard Flow unit such as XS, S, M, L and XL are compatible.

Most of the times, flow-rate peaks represent air bubbles. In order to get a stable measured flow rate, you have to remove all the air bubbles into your set-up. To achieve this, flush your set up by applying a higher pressure until air bubbles disappeared. Besides, you own flow controller might not deliver a stable flow. Contact us for more information.

Yes the diameter of the capillary is small: 25 µm, so depending on the size of your system, you may need to push your fluids harder to obtain a given flow-rate. Then the maximum pressure drop between the sides of the XS FLOW UNIT model at maximum flow-rate is 0.8 bar.

You can find cleaning procedures in the FLOW UNIT cleaning procedure. Concerning specifically the XS FLOW UNIT, it may withstand pressures up to 200 bar, so is it possible to use high pressure or flow-rate pumps in case of clogging.

It is possible to add a filter in the fluidic path. As an example, you can find among Idex products, biocompatible precolumn filters (references A-355, A-356). These filters are designed for use with 1/16’’ OD tubing. You can choose either 0.5 µm (A-700) or 2 µm (A-701) frit version to filter particles from you flow path.

For some fluid controllers, the settling-time may be long. For this reason, the transition phase after an order change in the fluid controller takes much longer, depending on the nature of the fluid controller. Visit us on www.fluigent.com for further information.

Some fluid controllers are unable to limit the fluctuations of the flow-rates around a mean ordered value because of the mechanical actuation they use. How to connect tubing to the FLOW UNIT models Therefore, the flow-rate within your system can be an imprecise response to the fluid controller. Visit us on www.fluigent.com for further information.

The FLOW UNITS have to be plugged to either  Flowboard or to FlOW EZ, which allows the communication between the FLOW UNITS and the computer.

The following section explains how you can calculate this scale factor and shows an example with a fluorinated oil: FC-40.
A method for providing a known flow-rate is required to work out the scale factor for the selected fluid. This could be a syringe pump, a peristaltic pump or a pressure regulator delivering fluid onto a precision balance with volume calculated from known density. Here is an example using MFCS™-EZ.
Make a table that contains the time for each measurement, results from weighing scale, the flow-rate of the pump and the data measured by the FLOW UNIT. A minimum of 3 measurements is recommended for each flow-rate.
The principle of the experiment is to inject the FC-40 through the desired FLOW UNIT model connected to the FLOWBOARD. Then simultaneously you record the flow-rate given by the software and you measure the weight of fluid you have collected over a chosen period of time. Knowing the density of the fluid, you are able to define the actual flow-rate.
Note that if a peristaltic or a syringe pump is used, one has to wait until the target flow-rate is reached (settling times can be long) and to calculate an average flow-rate due to the pulsations.

You can calculate a scale factor which will correct the measured flow-rate returned by the FLOW UNIT.
The different FLOW UNIT models are calibrated to provide an accurate reading when used with the corresponding fluid, water or isopropyl alcohol.
For the FLOW UNIT models XS/XL, only one single calibration for water is available. For the FLOW UNIT models S/M/L, two calibrations are available: Water and Isopropyl alcohol.
The FLOW UNIT can be used to handle different fluids not originally calibrated for. When possible, select a standard calibration field that most closely matches your fluid.
For example, water calibration can be used for water based solution and isopropyl alcohol calibration for hydrocarbons or oil. The calibration can be selected and switched in the software.
In order to obtain accurate flow-rates for alternative fluids, it is necessary to use correction factors (scale factor), to convert the displayed value into the actual value. The scale factor can be added in the software. Adding the scale factor ensures that the flow sensor reading is now accurate for the target fluid.

• The flow-rate calculated by the FLOW UNIT is based on a temperature diffusion-advection measurement with the glass capillary. If your fluid is not pure water (or isopropanol) you first need to add a scale factor to calibrate your FLOW UNIT.
• There might be a leak within your system. Please check if your system is completely tight before going any further.
• This might be because of your screwed fitting. Please unscrew and then re-screw it.
• Your fluid controller may not be as precise as the FLOW UNIT sensor.

The FLOW UNIT sensors are already temperature compensated, so they work in a range of 10°C to 50°C. This can be useful if your device needs to fit within an incubation chamber.

With the XS FLOW UNIT, the diameter of the capillary is small: 25 µm, so depending on the size of your system, you may need to push your fluids harder to obtain a given flow-rate. Then the maximum pressure drop between the sides of the XS FLOW UNIT model at maximum flow-rate is 0.8 bar.

In general, any cleaning by mechanical means should be avoided. Never enter the sensor flow path with sharp objects that could scratch the glass surface.

Furthermore, no abrasives or liquids containing solids that can grind the surface clean should be used. Anything that affects the glass wall will cause deviations in the measurement performance or permanently damage the sensor.

Strong acids and bases should also not be used to clean the sensor. Acids can sometimes be used in low concentration and at low temperatures. Before using the acid check how compatible it is with borosilicate 3.3 glass (Pyrex® or Duran®).

• Make a fresh 1% solution (10 grams per liter) in cold or warm water. If available, use warm water below 130F (55°C). For difficult soils, use very hot water (above 150F or 65°C) and use double the recommended amount of detergent.
• Circulate solution slowly for at least 1/2 hour.
• RINCE THOROUGHLY—preferably with running water.
• Drying can affect residues and corrosion. Impurities from rinse water can be deposited during evaporation. To minimize this, Dry with techniques that physically remove rinse water from the substrate such as isopropyl alcohol final rinse.