Viscosity sensor VLO-M1 for liquids

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The VLO-M1 viscosity sensor measures the viscosity of a fluid in a microelectromechanical system (MEMS system). In the sensor, the medium is passed through a pressure gradient to the omega chip, an omega-shaped microchannel. This vibronic measuring system generates the measured values by setting a silicon tube in the chip into resonant oscillation and analyzing it. This is because the vibration quality depends on the viscosity of the liquid in the microchannel. At the same time – and independent of the viscosity – the density of the medium to be measured can be determined via the frequency of the microchannel. Since the temperature influences both viscosity and density, the temperature of the medium is also recorded in the chip in real time. In this way, the temperature effect can be compensated.

The measuring system, which is sub-millimeter in size, enables the sensor to be compactly built. It is only 80 x 30 x 15 mm³ in size and can therefore be accommodated even in tight spaces.  The measured values are transmitted to the higher-level system via an RS232 interface and the ASCII command protocol in the TrueDyne Sensors standard.


Monitoring of fuel concentrations

New cars must be put through their paces before they are registered. The engine is tested at its limits and often started “cold”. As a result, the fuel no longer burns completely and it mixes with the engine oil. Too much fuel in the engine oil can destroy the engine. With the viscosity sensor, tests no longer have to be interrupted – you can monitor the viscosity of the oil directly in the process and replace it if necessary.


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1. Test bench for testing motors. 2. Engine under test. 3. Fuel used for the test. 4. Engine oil used in the engine. 5. The quality of the engine oil is tested directly in the process, damage due to possible contamination can be avoided.

Measured variable: 

Viscosity, Density and several metries derived from them (e.g. standard density, concentration, etc.)

Permitted media:

Particel free (<30 μm) hydrocarbons like for eg.

  • petrol E5 / E10 / E85
  • diesel B7 / B10 / XTL
  • Jet-A1 (also F-35 or JP-8)
  • M100 (methanol)
  • isopropanol
  • OME* (synthetic fuel)
  • LPG*

Aqueous media like for eg.

  • AdBlue®*
  • Glycole mixtures*

If necessary, media that deviate from the listed may be used, after individual clarification. *Optional

Accuracy of measurement:

Viscosity: ±[0.2 mPa s + 5% of measured value]
Density: ±[0.2 or 0.01 x abs (T-25 °C)] kg/m³ if the value is >0.2
Temperature: ±0.15 or. ±[0.0075 x abs(T-25 °C)] °C if the value is >0.15


Viscosity: ±0.1 mPa s
Density: ±0.1 kg/m³
Temperature: ±0.05 °C

VLO-M1 max measurement error

Temperature conditions
Permitted medium temperature:

-20…+60 °C

Permitted ambient temperature:

-20…+60 °C

Permitted storage temperature:

-20…+60 °C

Range of application
Permitted viscosity range

0,3…50 mPa s

Permitted density measurement range:

600…1000 kg/m³ (Option 0…1200 kg/m³)

Permitted process pressure range:

0…20 bar (absolute)
Bursting pressure 80 bar (absolute)

Permitted particle size:

Max. 30 μm

Permitted flow range:

0…10 l/h (water)


Due to the high operating frequency of the micro channel, vibrations (<20 kHz) do not affect the measuring accuracy.

Inlet and outlet runs:

Inlet and outlet runs do not affect the measuring accuracy.

Ambient conditions

IEC/EN 60068-2-1
IEC/EN 60068-2-2
IEC/EN 60068-2-30

Elektromagnetische Verträglichkeit:

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

Schwingungs – und Stossfestigkeit:

IEC/EN 60068-2-6
IEC/EN 60068-2-27
IEC/EN 60068-2-64


Stainless steel:

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

Medium wetted material:

Stainless steel:

  • 1.4542 (AISI/SUS 630)

BOROFLOAT® 33 glass
Epoxy resin

Dimensions / design


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


<150 g

Dimensions measuring channel:

160 x 200 μm (500 nl)

Housing protection:

IPx4, IPx5, IPx6, IPx7 (IEC 60529)

Fluidic interfaces
Fluidic interfaces:

2 x M5 threaded holes with an angle of 45° to the side and the front surface

Electrical interfaces
Cable type:

Fixed installed cable

Cable length:

3 m

Outer diameter of cable:

2.3 mm

Diameter of cores:

4 x AWG 28

Lead of gage:

Digital communication line and power supply in a common shielded cable


Continuous, without the need for a command from the outside
Hardware Standard RS232 Proprietary ASCII output string

String VLO


Power supply:

Power connection DC 5 to 12 V (max. 400 mW) via power unit with safety extra low voltage (SELV) or protective extra low voltage (PELV)

Voltage strength

The maximum permissible fault voltage between GND (signal ground) and earth must not exceed 36 Vpeek.

Data rate:

10 Saps
(Option acyclique with 100 ms response time)

Cable occupation:

white: VDD (supply voltage)
brown: GND (signal ground)
green: RX (input)
yellow: TX (output)

Note: The cable assignment corresponds to the view of the sensor (VLO-M1)

Certificates and approvals
CE mark:

The density sensor meets the legal requirements of the EC Directives. TrueDyne Sensors AG confirms that the density sensor has been successfully tested by applying the CE mark.


All installed components meet the requirements of the RoHS directive.

Electromagnetic compatibility:

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

Product design

Product Design: VLO-M1

  1. Housing
  2. Electronic interface for communication and power ­supply
  3. Drill holes for mechanical mounting (6 x M3 threaded holes)
  4. Fluidic interface (2 x M5 threaded holes)


1080x810px_DGF-M1_mechanische Befestigung_1901_TrueDyne_Dichtesensor

Mechanical mounting: VLO-M1

DLO-M1_VLO-M1_fluidischer Anschluss

Fluidic installation: VLO-M1