DGF-I1 density sensor for gases

Measure the density of a gas directly in the gas line or in the gas tank: This is made possible by the DGF-I1 density sensor from TrueDyne. At the heart of the sensor is a microelectromechanical system (MEMS) with an oscillator in the form of a tuning fork. For the measurement, the metal housing surrounding the MEMS is filled with the medium. The natural frequency of the oscillator varies depending on the density of the gas surrounding it. In order to compensate for temperature effects, a platinum resistor which precisely measures the local temperature is built into the sensor.

The sensor is very compact with a diameter of 31 mm and a length of 63 mm and can be placed in even the smallest of spaces. It is screwed directly into the gas line or the gas tank with the integrated connection, and a filter protects against contamination. The measured values are transmitted to the higher-level system via an RS485 interface. The response time of 5 seconds enables density measurement directly in the process – the measurement does not have to be interrupted.


Monitoring of welding gas mixtures

For a strong weld seam, the gases used must be correctly mixed. However, mechanical valves can move and leaks or mix-ups can lead to the mixing ratio no longer being correct. Up to now, it has only been possible to check the gas used by means of random sampling. With the TrueDyne sensor you can monitor the quality of your welding gas directly in the process. With the density data and with the help of tables and calculation algorithms, the concentration of the gases used can be precisely determined and reported to the customer.

1. Welding device. 2. Gas mixer which mixes the gases used for welding. 3. TrueDyne’s DGF-I1 density sensor measures the density of the gas mixture directly in the process. If this deviates from the nominal value, the process can be interrupted immediately. 4. Thanks to the ongoing quality control of the gas used, you can weld without rejects.

Monitoring of gas mixtures for food packages

Meat or fresh salads are packaged in a protective atmosphere so that they have a longer shelf life and do not turn brown. As standard, individual food bags are pierced after filling and the gas inside them is tested. If the result is inadequate, the entire production batch must be discarded. With the density sensor from TrueDyne, you can check the quality of the gas mixture in real time and directly in the packaging process – spot checks are no longer necessary and there is less waste.

1. Gas cylinders for the filling of food packages (mostly CO2 and N2). 2. Gas mixer. 3. The two gases, A and B, are mixed. 4. The DGF-I1 is integrated directly into the production process. The sensor measures the density of the gas mixture in real time and directly in the packaging process. 5. Food is packaged in a protective atmosphere. If the density measured by the sensor deviates from the nominal value, production can be interrupted.

Monitoring of clean gas

Gases are often colorless and odorless, they can be rather expensive, and damage can occur – previously, it was only possible to check whether the right gas was being taken out of storage or introduced into a process by means of random sampling. With the density sensor from TrueDyne, you can determine the density of a gas and thus the quality directly during operation. This prevents mix-ups and rejects.

1. Clean gas storage: A cylinder containing gas C has been incorrectly stored among cylinders containing gas A. 2. Pressure reducer. 3. The DGF-I1 is integrated into the filling system and measures the gas density in real time. If gas C is introduced, it detects the deviating density and stops the filling process. 4. If the DGF-I1 determines that the density of the gas is correct, the process continues. 5. The correct gas is used and the quality is guaranteed at all times.


Measured variable:

Density in kg/m³
Temperature in °C
Pressure in bar absolute

Derived measured variables (customer-specific configuration):

  • Concentration of binary gas mixtures, ideal volume percentages (=molar percentages ) in %
  • standard density
  • Average molar mass
  • Customer-specific measured variables

Permissible media:

Hydrogen (H2)
Helium (He)
Nitrogen (N2)
Oxygen (O2)
Carbon dioxide (CO2)
Neon (Ne)
Argon (Ar)
Krypton (Kr)

Media that deviate from those listed above may be used after individual clarification if necessary.

Accuracy of measurement::

Density: <0,1 kg/m³
Temperature: ±0,8 °C
Pressure: ±0,04 bar
With field calibration density: <0,05 kg/m³


Density: ±0,015 kg/m³
Temperature: ±0,06 °C
Pressure: ±0,005 bar

Temperature conditions
Permitted medium temperature:

-20…+60 °C

Permitted ambient temperature:

-20…+60 °C

Permitted storage temperature:

-20…+60 °C

Range of application
Permitted density measuring range: 

0,2 …19 kg/m³

Permitted pressure range:

1…10 bar (absolute)
Burst pressure 30 bar (absolute)


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

Environmental conditions
Climate class:

Not specified

Electromagnetic compatibility:

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

Vibration and shock resistance:

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


Stainless steel: 1.4404 (316L)

Electromagnetic compatibility:

Stainless steel: 1.4404 (316L)
electronic board

Dimensions / Design


63 mm x 27 mm x 32 mm³ (with M8 plug)


<150 g

Housing protection:

IPx7 (IEC 60529)

Fluidic interface
Fluidic interfaces:

M22x1.5 thread
Adapter G½” thread ­(order opition)

Electrical interface

M8 connection, 4-pin, according to IEC 61076-2-104


Continuous, without the need for an external command.
On the hardware standard RS485.
Proprietary Modbus RTU communication protocol.

Power supply:

DC 4.5…12 V (max. 200 mW)
Connection cable and plug are not included in the scope of delivery. Requirements for connection cable, power supply unit and plug:

  • Power supply unit with safety extra-low voltage (SELV) or protective extra-low voltage (PELV).
    M8 plug, 4-pin
    Maximum permissible cable length:30 m
    Cable recommendation: Lumberg Automation M8 Standard Sensor / Actuator Connectors RKMWV 4-07

RS485 interface:

According to standard EIA/TIA-485-A
Maximum permissible voltage:

  • A and B: -11 V…+15 V
    (A-B) or (B-A) with active termination: 6 V

Switchable 120 Ω termination:

Pin assignment M8 connection:

1 V+      supply voltage
2 A        Modbus RS485
3 GND  signal ground
4 B        Modbus RS485

Integrated filter

sinter bronze 50 µm (theoretical pore size)

Certificates / Approvals

CE mark:

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


All installed components meet the requirements of the RoHS directive.

Electromagnetic compatibility:

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

Accessories and spare parts
Adapter fluidic:

Adapter “G½” thread for the fluidic interface.

Adapter electric:

USB-RS485 incl. M8 plug

Sealing ring:

Sealing ring for the replacement of a damaged sealing ring
(available for the respective fluidic connection – M22x1.5 or “G½” thread).


Set consisting of filter, spring washer and retaining ring for the replacement of a dirty filter.