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Density sensor DLO-M2 for liquids

The DLO-M2 sensor measures the density of liquids in a microelectromechanical system (MEMS system). Within the MEMS system, the liquid is directed to an omega-shaped microchannel, the so-called omega chip. This tiny silicon tube – it is hardly thicker than a hair – is set into oscillation for the measurement. The density of the medium can be derived from the natural frequency of this oscillation: the denser the medium, the lower the oscillation.

Thanks to the measurement in the MEMS system, the sensor is only 30 x 80 x 15 mm in size and can be accommodated even in tight spaces. The high-precision measurement results are immediately available, allowing continuous measurement during the process. The density of liquids depends on their temperature. To compensate for this effect, an integrated platinum resistor detects the temperature of the liquid.

The density sensor sends the measured data to the readout system via the data line in Modbus RTU transmission mode.



Product description

Modbus RTU

Modbus RTU

  • Modbus RTU
  • RS-485 point-to-point connection
  • Modbus over serial line – Specification
Modbus RTU

Inline measurement

  • Directly in the running process
  • Values are output instantaneously
  • Quick change of media possible


  • Density value
  • Max. measurement deviation: ±0.5 kg/m³
  • Repeatability: ±0.25 kg/m³


  • Hydrocarbons
  • Aqueous media
  • and much more – Ask us
Icon Concentration

Concentration packages (option)

  • Sugar / water according to ICUMSA (%mass)
  • NaCl / water according to Laliberté / Cooper (%mass)

Continuation of concentration packages

  • High-fructose corn syrup HFCS42, HFCS55, HFCS90 (%mass / °Brix / °Plato / °Balling)

Continuation of concentration packages

  • Ethanol / water according to OIML IST-90
    (%mass / %vol@20 °C / ABF@20 °C)

Continuation of concentration packages

  • Methanol / water (%mass)
  • Ethylene glycol / water in (%mass)

Continuation of concentration packages

  • Mineral content in water according to Huber (mg/l)
  • Hydrogen peroxide in water (H2O2) (%mass)


From volume (l) to mass (kg)

For example, when a fuel is pumped from a truck into a tanker, the volume of the refuelled liquid is recorded as standard. However, since the density varies according to pressure and temperature, it is not possible to make precise statements about the mass. With the DLO-M2 sensor from TrueDyne, you can collect the necessary data on the density during the process and use them to calculate the mass (V-ρ=m).


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1. Fuel is pumped from the truck to the tanker. 2. Standardised volumetric measurement in litres. 3. Installed in a bypass line, the density sensor DLO-M2 measures the density directly on the truck. Thanks to the compact design of the sensor, it can also be retrofitted into the process. 4. Together with the volumetric measurement, the density can be used to calculate the mass of the fuel in kilograms, which is then handed over to the customer.

Concentration monitoring

In most cases, the refrigerant in a cooling circuit consists of a mixture of ethylene glycol and water. The optimum concentration is determined depending on the minimum temperature entering the circuit to prevent the liquid from freezing. At the same time, the aim is to keep the water content as high as possible, as this has a positive effect on the thermal conductivity. So how can the concentration of the glycol-water mixture be monitored in the process? With TrueDyne’s DLO-M2 sensor, you collect the data you need to determine the concentration of the medium in the running process.


1. Density sensor with integrated glycol-water concentration calculation. 2. The concentration is output directly as a measured value. 3. Refrigeration plant and preparation of the concentration for cooling industrial applications. 4. Heat exchangers on the roof of factory buildings. Due to the circulation, water can evaporate and the concentration of the refrigerant changes. This is where the DLO-M2 is used for concentration monitoring.

Beer application

Alcohol is produced by fermenting a sugar source with a catalyst, typically yeast or certain bacteria. In the process, the carbohydrates (sugar and starch) are converted into carbon dioxide and ethyl alcohol. This serves as the basis for all alcoholic beverages, regardless of whether they are beer or spirits such as gin and whiskey.

In order to be able to make a statement about the progress of the fermentation process, measurement samples must be taken and analysed regularly. This is exactly where TrueDyne’s DLO-M2 density sensor with integrated concentration determination comes in. Even with small sample volumes, a precise indication of the progress of the fermentation process is possible.


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1. Taking a sample from a fermentation tank. 2. Preparation of the sample by degassing and filtering of turbid and suspended matter. 3. Density measurement with integrated concentration calculation of sugar in water. This enables a precise statement about the progress of the fermentation process. 4. Disposal of the test sample. Due to the sensor design and the resulting low sample volume, hardly any rejects are generated.


Quality monitoring

The density of a liquid depends on its composition. If different liquids are mixed, the correct mixing ratio can be checked with density measurements. For example, in the case of heating oil: according to the legal requirements, 7% biodiesel may be added to heating oil. Since this is tax-free, it is often used on the border of legality. With the DLO-M2 density sensor from TrueDyne, they monitor the quality of the heating oil in the running process.


1. Tanker truck for the delivery of heating oil. 2. The sensor measures the density of the heating oil directly at the transfer point. The data collected on site shows whether the right media are being refuelled in the correct ratio. 3. The product is handed over to the customer. Good quality is guaranteed.



The density sensor was designed to measure the density of fluids. This is done with a microelectromechanical system (MEMS) with an omega-shaped microchannel (omega chip) built into an internal bypass.

When a liquid flows through the density sensor, the bypass arrangement creates a pressure gradient across the microchannel, allowing the liquid to reach the omega chip. The liquid influences the physical properties of the excited sensor (resonance frequency and quality), these are digitalised and evaluated in the microcontroller. The measured values can be read out via the serial interface (RS-485, Modbus).

Thus, density measurements in the range 600…1,000 kg/m3 (for further options see product specifications) can be realised at a flow rate of 0…10 l/h. settings.

Omega Chip

The Omega chip, a vibronic microsystem, is the heart of the measurement system and serves to generate the sensor signal in the overall system. The essential component of this microsystem is a silicon tube (microchannel) which is vibrated electrostatically in a vacuum. To compensate for temperature effects, a platinum resistor is integrated, which allows local real-time temperature detection. The Omega chip consists essentially of crystalline silicon and glass.

Measuring principle omega chip

Measuring principle (omega chip)

Density measurement

For density measurement, the density sensor uses the omega chip. The filled microchannel is set into resonant oscillation and analysed.

The resulting natural frequency of the microchannel depends on the mass and thus on the density of the medium in the microchannel: the greater the medium density, the lower the natural frequency. The natural frequency is thus a function of the density of the medium.


f = natural frequency, E ⋅ I = tube stiffness, ρTube = tube density, ATube = tube cross-section, ρFluid = fluid density, AFluid = fluid cross-section.




Density and variables derived from it (e.g. standard density, concentration, etc.)

Typical media:

Particulate free (<30 μm) media such as

  • Gasoline, diesel, kerosene
  • OME (synthetic materials)
  • Oils and lubricants
  • Water-based media
  • Methanol, ethanol, isopropanol
  • LPG*
  • AdBlue®*
  • Glycol mixtures*

Other media can be used after individual clarification. *Optional

Concentration packages:

  • Various sugars in water
  • Invert sugar in water
  • High fructose corn syrup
  • Methanol in water
  • Ethanol in water
  • Salt in water
  • Minerals in water
  • Hydrogen peroxide in water
  • Ethylene glycol in water
  • Butane in propane

Note: User-specific concentration packages on request

Measurement performance

Max. measurement deviation:

Density: ±0,5 kg/m³ (option ±[0.2 kg/m³ or 0.0075 x abs (T-25 °C)] kg/m³ if the value is >0.2 kg/m³)
Temperature: ±0,3 °C (option ±0.15 °C or ±[0.005 x abs(T-25 °C)] °C if the value is >0.15 °C)


Density: ±0,25 kg/m³ (option ±0,1 kg/m³)
Temperature: ±0,1 °C (option ±0,05 °C)

DLO-M2_ex - Maximale Messabweichung

Temperature conditions

Permissible medium temperature:

-40 …..+60 °C

Permissible ambient temperature:

-40 …..+60 °C

Permissible storage temperature:

-40 …..+60 °C


Permissible density measuring range:

600…1,000 kg/m³ (option 0…1,200 kg/m³)

Permissible viscosity range:

0.3…5 mPa s (option 0.3…50 mPa s)

Permissible pressure of medium:

0…20 bar (abs)
Burst pressure: 80 bar (abs)

Permissible particle size:

Max. 30 μm

Permissible flow rate range:

0…10 l/h (water)


Vibrations (<20 kHz) have no influence on the measuring accuracy due to the high working frequency of the microchannel.

Inlet and outlet sections:

Inlet and outlet sections have no influence on the measuring accuracy.

Ambient conditions

Climate class:

Not yet defined

Electromagnetic compatibility:

EMC 2014/30/EU (EN 61326-1)

Vibration and shock resistance:

Not yet defined

Degree of protection:

IP54 (IEC 60529)



Stainless steel:

  • 1.4404 (316L)
  • 1.4542 (AISI/SUS 630)

In contact with media:

Stainless steel:

  • 1.4542 (AISI/SUS 630)

BOROFLOAT® 33 glass
Epoxy resin

Dimensions / Design
















Type: DLO-M2_ex (On the DLO-M2 (not Ex) the clamping bracket is omitted on the earthing plate with M3×8 TORX screws – Marked orange in the diagram


30 mm x 66 mm x 15 mm (without cable and cable gland)


<200 g

Dimensions of measuring channel:

160 x 200 μm (500 nl)


Fluidic interfaces

Fluidic interfaces:

2 x M5 threaded holes at a 45° angle to the side and front surfaces

Electrical interface


Continuous, without the need for an external command.
On the hardware standard RS485.
Proprietary Modbus RTU communication protocol (see data sheet)

Cable design:

Permanently installed cable. Connection cable type KS-Li9YD11Y 4xAWG 28, manufacturer: Kabel Sterner

Cable length:

3 m (option up to 30 m)

Cable outer diameter:

2.3 mm

Wire diameter:

4 x AWG 28

Level control:

Digital communication lines and power supply in one common shielded cable, unidirectional, RS-485
Provide termination resistance of 330 Ω on the client side

Energy supply:

Maximum current consumption 26 mA
Maximum power consumption 350 mW

Supply: 5 V…13.3 V

Dielectric strength:

The reference potential (GND) is connected to the housing and the earth connection (see product structure). There is no electrical isolation between the supply circuits, the communication interface and GND

Data rate:

Response time: 100 ms

Cable assignment:

Wire colour assignment

  • yellow – RS485 B, D1
  • green – RS485 A, D0
  • brown – GND (signal ground), common
  • white – VDD (supply voltage)
  • blank – shielding
Certificates / Approvals

CE mark:

The density sensor meets the legal requirements of the EC directives. TrueDyne Sensors AG confirms successful testing of the density sensor with attachment of the CE mark.



  • LVD 2014/35/EU (L96/357)
  • EMC 2014/30/EU (L96/79)
  • RoHS 2011/65/EU (L174/88)


  • EN 61010-1:2010
  • EN 61326-1:2013
  • EN 61326-2-3:2013
  • EN 50581: 2012
Product structure

DLO-M2 – Product structure











Product structure:

  1. Density sensor DML02(_ex)
  2. Mounting holes for mechanical fastening (6 x M3 threaded holes)
  3. Fluidic interface (2 x M5 threaded holes)
  4. Clamping bracket on earthing plate with screws M3×8 TORX
  5. Electronic interface for communication and power supply

For the DLO-M2 (not Ex), point 4 (clamping bracket on earthing plate with M3×8 TORX screws) is omitted.
Marked orange in the diagram.


1080x810px_DGF-M1_mechanical mounting_1901_TrueDyne_density sensor

Mechanical fastening: DLO-M2