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Bidirectional flow sensor

The FLOW UNITs are bidirectional flow rate sensors compatible for stand-alone use with the Line Up™ controllers, or with any other microfluidic control system such as the MFCS™ series using the Flowboard hub. Available in 5 flow rate ranges, the FLOW UNIT allows for pressure regulation using the DFC (Direct Flow Control) algorithm  to monitor or control the system by flow rate instead of pressure.

Main benefits
  • Compact

    Uses minimum bench space

  • Adaptable

    Use with or without a PC

  • Intuitive

    Straight forward set up & use

  • Wide range

    Measurement from nL to mL


Tune measurements for various liquids

When combined with a FLOW UNIT, one can A scale factor can be added to your measurements when handling other fluids than the liquid for which the flow sensor is calibrated for. For organic solutions, a second calibration with isopropyl alcohol is built-in on the FLOW UNIT models S, M and L.

Flow rate measurement

The FLOW UNIT is a unique tool to easily monitor flow-rates in any microfluific system with the best precision & accuracy. A micro heater provides a minimal amount of heat to the medium monitored. Two temperature sensors, located on both sides of the heat source, detect  temperature variation. The flow-rate is then calculated based on the thermal desorption, which is directly related to the flow-rate.

Monitor & Control experiments

Flow-rate measurements (bidirectional) for all FLOW UNITs are displayed in FLUIGENT software. An additional function displays and records the dispensed volume for each FLOW UNIT. Flow-rates can be directly controlled with the MFCS™ series and LineUp™ series intruments using the DFC, “self-learning” flow rate control algorithm.

Precision for various flow rate ranges

The different FLOW UNIT models offer an extensive choice of flow-rate ranges to best match your needs over the range of 7nL/min to 5mL/min.

Locally control flow rate

Combined with a LineUp™ Push-Pull or a LineUp Flow EZ™ one can monitor or control  flow rate without a PC.


Sensor diameter25 µm150 µm 430 µm 1.0 mm 1.8 mm
Dead volumeNoneNoneNoneNoneNone
Maximum pressure200 bar200 bar 100 bar 15 bar 15 bar
Wetted materialsPEEK
& Quartz Glass
& Quartz Glass
& Borosilicate Glass
& Borosilicate Glass
& Borosilicate Glass
Calibrated mediaWater





Accuracy (m.v.= measured value)
also applies to negative values
10% m.v. above 75 nL/min
7.5 nL/min below 75 nL/min

5% m.v. above 0.42 µL/min
21 nL/min below 0.42 µL/min

20% m.v. above 4.2 µL/min
210 nL/min below 4.2 µL/min
5% m.v. above 2.4 µL/min
0.12 µL/min below 2.4 µL/min

20% m.v. above 25 µL/min
5 µL/min below 25 µL/min
5% m.v. above 0.04 mL/min
1.5 µL/min below 0.04 mL/min

20% m.v. above 0.5 mL/min
100 µL/min below 0.5 mL/min
5% m.v. above 0.2 mL/min
10 µL/min below 0.2 mL/min

Repeatability (m.v.= measured value)
also applies to negative values
<1% m.v. above 90 nL/min
0.9 nL/min below 90 nL/min

0.5% m.v. above 0.7 µL/min
3.5 nL/min below 0.7 µL/min

1% m.v. above 0.7 µL/min
7 nL/min below 0.7 µL/min
0.5% m.v. above 1.4 µL/min
8 nL/min below 1.4 µL/min

1% m.v. above 25 µL/min
0.25 µL/min below 25 µL/min
0.5% m.v. above 0.04 mL/min
0.2 µL/min below 0.04 mL/min

1% m.v. above 0.5 mL/min
5 µL/min below 0.5 mL/min
0.5% m.v. above 0.2 mL/min
1 µL/min below 0.2 mL/min


Control in real-time, protocol automation, data record and export
ver. or more recent

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Software Development Kit

Custom software application
ver. or more recent

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Flow rate control without a PC
Flow rate control with Fluigent software

Connect the USB cable between the computer and the Flowboard. The green led is now switched on.

Connect the FLOW UNIT on the Flowboard

Integrate the FLOW UNIT to the microfluidic system with the dedicated tubing & fittings.

For L or XL FLOW UNIT model:

  1. Cut the 1/16’’ OD tubing to the desired length, leaving a square-cut face.
  2. Slide the nut over the tubing with the nut thread facing the tubing end being connected.
  3. Slip the ferrule over the tubing, with the tapered portion of the ferrule facing the nut. NB: the nuts and ferrules are specifically designed to work together. FLUIGENT advises you to only associate the provided ferrules with the provided nuts and vice-versa.
  4. Insert the assembly into the receiving port, and while holding the tubing firmly against the bottom of the port, tighten the nut finger tight.
  5. To check the tightness of your connection, you may pull gently on the tubing: it must stay fitted in the ferrule and nut.
  6. Do the same thing on the 2nd port.

For XS, S or M FLOW UNIT model:

  1. Cut the 1/32’’ OD tubing to the desired length, leaving a square-cut face.
  2. Slide the fitting over the tubing.
  3. Insert the assembly into the receiving port, and while holding the tubing firmly against the bottom of the port, tighten the fitting finger tight.
  4. To check the tightness of your connection, you may pull gently on the tubing: it must stay fitted in the ferrule and nut.
  5. Do the same thing on the 2nd port.
    • Note: Please verify you connect the FLOW UNIT in the right direction by checking the arrow on the sticker.
    • Check the provided kits with your FLOW UNITs as they can be different according to their model.

FLOW UNIT models are highly sensitive and should be properly cleaned to always maintain high performance. With proper care and maintenance, the FLOW UNITs can last many years. No cleaning or improper cleaning may leave deposits on the internal capillary wall which could result in measurement deviations and even clogging. Cleaning the sensor after use and before storing the device for a long period of time should prevent the sensors from any damage.
Do not allow the sensor to dry with media in the capillary tube without flushing clean first. Also try to avoid letting the filled sensor sit for extended periods (depending on your liquid).
Before storing the sensor, always drain of fluid, flush with cleaning agent, blow out, and dry the capillary.

For the XS FLOW UNIT model, filter your solution through a 5µm (or lower) membrane filter.

Cleaning and flushing of the FLOW UNITs should consider the nature of the materials that were being pumped through them. Typically, one should select a cleaning solution that is safe for the FLOW UNIT (the inside surface) and the rest of the set up but yet will dissolve the type of samples that were in contact with the surface.
For FLOW UNIT XS, S and M, fluids have to be compatible with PEEK & Quartz glass.
For FLOW UNIT L and XL, fluids have to be compatible with PEEK & Borosilicate glass.

The following steps are recommended for water-based solutions, in the right order:
• Rinse all your system with water.
• Clean the FLOW UNIT with a non-foaming detergent.
The detergent needs to be compatible with FLOW UNIT, the rest of your set-up (microfluidic chip, especially) and fluids used during your experiment.
• Remove all the contaminants thanks to a disinfectant (for example, Javel bleach).
• Rinse the Javel bleach (or the selected disinfectant) with water.
• Rinse all you system with isopropanol. Thanks to this final step, you won’t leave any trace on your Flow Unit.
• Then, sensor yellow plugs must be installed for storage

Working with multiple liquids
Switching between multiple liquids can leave transient deposits in the form of liquid layers inside the glass capillary. This is especially common for insoluble liquids, but can happen even with miscible liquid combinations. For example, when IPA is followed by water in a sensor without drying in between, large offsets can be observed for hours after switching to water. If possible, dedicate a separate sensor for each different liquid to be measured. If not possible, use caution when switching media and clean properly.

Working with water
When working with water it is recommended not to let the sensor dry out. All salts and minerals in the water will deposit on the glass and are difficult to remove. Although salt solutions are particularly prone to problems, even clean water can still contain enough dissolved minerals to form a deposition layer. Flush with DI water on a regular basis to prevent build-up. If you still encounter problems, occasionally flush the sensor with slightly acidic cleaning agents.
When working with water containing organic materials (sugars, etc.) microorganisms often grow on the walls of the glass capillary and form an organic film that can be difficult to remove. Flush on a regular basis with solvents such as ethanol, methanol or IPA, or with cleaning detergents to remove organic films.

Working with silicone oils
When working with silicone oil it is recommended not to let the sensor dry out. Silicone oils can be cleaned out using special cleaners. Check with your silicone oil supplier for cleaning agents compatible with glass surfaces.

Working with paints or glues
When working with paints or glues it is critical not to let the sensor dry out. Often, depositions of paints and glues cannot be removed anymore after they have dried. Flush the sensor with cleaning agents recommended by your paint or glue manufacturer that are compatible with glass. Ensure that you have found a good cleaning procedure before performing the first tests, and always clean shortly after emptying the sensor.

Working with alcohols or solvents
Unlike most other fluids, alcohols and solvents are not critical and a short flush of isopropanol (IPA) is sufficient to clean the capillary walls.

Other liquids or applications
If uncertain about your application and how to clean the flow sensor, please contact FLUIGENT for additional support at support@fluigent.com

• 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.

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®).

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.

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.

• 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.

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.

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 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.