The great advantage of MEMS technology for flow measurement

MEMS (Micro-Electro-Mechanical Systems) is changing the way mass flow is measured. Smaller, more stable and with better long-term stability than classic capillary sensors: the MEMS sensor is not just an evolution, but a fundamentally different approach.

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What is a MEMS sensor?

A MEMS sensor is a tiny electromechanical system fabricated on a silicon chip, the same technology used for processors and memory chips. The foundation was laid in 1974 by Anton van Putten and Middelbeek, students at Delft University of Technology, who made a flow sensor on silicon as a study assignment. Without knowing it, they had invented the first thermal mass flow sensor on a silicon chip.

For flow measurement, MEMS means that heating elements and temperature sensors are placed directly in the gas stream on a microscale, on a single silicon chip. The most widely used variant is the calorimetric sensor: a heating element in the middle, with two temperature sensors (thermopiles) on either side.

With no flow, T1 and T2 are equal. As soon as there is flow, the gas cools the upstream thermopile and heats the downstream one. The temperature difference ΔT is directly related to the mass flow. However, every MEMS sensor behaves slightly differently; there is no sensor-to-sensor repeatability, so each unit must be calibrated individually after assembly.

The advantages of MEMS for flow measurement

1. Calibration with real gas: maximum accuracy for every gas

No assumptions, no conversion factors

Every gas has unique thermal properties: specific heat (Cp), thermal conductivity (λ) and density (ρ). The MEMS sensor responds to all these properties together, via a non-linear curve that differs per gas. This makes it possible to calibrate the meter with the actual process gas and thus achieve the highest accuracy, precisely tailored to your gas and your measuring range.

The Vögtlin red-y series is calibrated with the real gas as standard: air, O₂, N₂, He, Ar, CO₂, H₂, CH₄, C₃H₈ and, on request, with other mixtures or gases. Every calibration is NIST-traceable over the full range. Want to switch gases quickly without recalibration? The red-y also offers gas conversion factors in its memory, so you can easily switch in the software.

2. Virtually no drift: stable for years

Proven in practice, not just on paper

The MEMS chip is made of silicon in a clean semiconductor process. There are no windings, no bent metal tubes and no organic insulating layers that age. The measuring principle is therefore inherently stable; the silicon substrate does not change under thermal cycling.

Vögtlin demonstrated this with an analysis of "as found" certificates: meters that came back for calibration after years of use. Only a small proportion were outside specification, and most of those had demonstrably been contaminated by the measured gas, not by sensor drift. As long as the sensor is not contaminated, you can expect years of stability.

3. Wide measuring range in one instrument, turndown 1:100

From 1% to 100% of full scale

The MEMS sensor delivers reliable measurements over a turndown ratio of 1:100, i.e. from 1% to 100% of the set range with the specified accuracy. This is exceptionally wide for a thermal flow meter and avoids the need for multiple instruments for processes with strongly varying flows. An even greater turndown range is possible on request.

4. Extremely fast: response time of 80 milliseconds

Suitable for dynamic and pulsating flow processes

Thanks to the minimal thermal mass of the MEMS chip, the sensor responds extremely quickly to changes in the gas flow. The red-y smart meter (GSM) achieves a response time of ±80 ms; the controller (GSC) ±500 ms including valve control. The warm-up time to full accuracy is less than one second after switching on.

This makes the MEMS meter ideally suited to applications with rapid setpoint changes, pulsating flows or processes in which the response time of the measuring system directly affects the process result, such as bioreactors, gas chromatography and fuel cell applications.

5. Low pressure drop and less sensitive to contamination

Robust in less clean processes

The MEMS sensor is located in a relatively wide flow path. This results in a low pressure drop across the instrument, typically 2.5 mbar at low flow, which makes the system suitable for pressure-sensitive applications. In addition, small particles or contaminants in the gas can pass the sensor without immediately clogging the instrument, which increases system availability.

6. Compact, lightweight and energy-efficient

Ideal for OEM integration and modular set-ups

A MEMS chip consumes only milliwatts of power and, thanks to its small size, is easy to build into compact equipment. The red-y compact even runs on a standard AA battery. The modular design also makes it possible to mount several units side by side on a single gas distribution block, which is useful for gas mixing panels in which several gases are dosed in parallel.

Points to consider

The MEMS sensor is not intended for corrosive or aggressive gases that can attack the sensor surface. Do not use the meter below 200 mbar absolute in the sensor section; below this limit, molecular flow occurs (high Knudsen numbers), which disrupts the thermal measuring principle. Incidentally, vacuum downstream of the valve of an MFC is not a problem. Moisture in the gas can damage the sensor; see our article on measuring mass flow in wet hydrogen.