Wink of knowledge: Air & N2 – DGF-I1 density sensor for gases

Season 1 | Episode 1

Why this test?

The measurements performed in a series of various quick tests are intended to demonstrate how precisely the DGF-I1 density sensor for gases works in operation.
Since air and nitrogen have a similar density range, the test results confirm our expectations for the DGF-I1 density sensor.

What is a wink of knowledge?

Do you sometimes need to measure, draw or make something quickly?
And the speed at which you get to the result counts more than the perfect (scientific) approach?
For this reason, we have introduced a wink of knowledge.
Science with a twinkle in its eye, so to speak.
We’re not looking to prove something scientifically, but rather to quickly demonstrate something pragmatically. If you’re interested, we would be happy to discuss these results in more detail with you and your project.

Which gases were used?

  • Nitrogen 4.5

    PanGas (material number 6430112)

  • Dry air

    Air compressor

Density measurement

The density was measured with the gas density sensor DGF-I1.
For this purpose, the listed gases were passed through the sensor for a period of time at a constant flow rate.
A logging function was used to record a reading for the density, temperature, pressure and reference density once every second.

Nitrogen (N2)

1.2503 kg/m³

at 0 °C, 1.01325 bar abs

Dry air (Air)

1.292 kg/m³

at 0 °C, 1.01325 bar abs

The TrueDyne sensor

With a diameter of 33.5 mm and a length of 63 mm, the DGF-I1 density sensor has a very compact design and fits into the smallest of spaces.
It is screwed directly into the gas pipe or gas tank with the integrated connection; a filter protects against contamination.
The readings are transmitted to the higher-level system via an RS485 interface.
The response time of 5 seconds makes a density measurement directly in the process possible – the measurement does not have to be interrupted.

Permissible media:

Hydrogen (H2) • Helium (He) • Nitrogen (N2) • Oxygen (O2) • Carbon dioxide (CO2) • Argon (Ar)

Media which differ from the media listed above can be used after individual clarification, if necessary.
For example Neon (Ne) and Krypton (Kr).

 

DGF-I1 density sensor with size indication
DGF-I1 density sensor for gases
Max.
deviation:

Density: <0.1 kg/m³

Temperature: <0.8 °C

Pressure: <0.04 bar

With field adjustment density <0.05 kg/m³

Repeatability:

Density: <0.015 kg/m³

Temperature: <0.06 °C

Pressure: <0.005 bar

Permissible density measuring range:

0.2 … 19 kg/m³

 

Permissible pressure range:

Max.
measurement range:

1…10 bar (absolute)

Gas mixtures with argon (Ar) only up to

max. 9 bar (abs) must be used.

Burst pressure 30 bar

Test setup

Figure 1 shows the structure of the test station.
Five thermal mass flow controllers (MFC) connected in parallel allowed the various pure gases to flow through the sensor in alternation.
The installation of the exhaust at the side opening of the sensor favours the gas exchange in the housing, which optimises the reaction time.

 

  1. Gas supply
  2. MFC: Vögtlin red-y GSC-B9SA-BB23
  3. Static mixer: Swagelok
  4. Density sensor: TrueDyne DGF-I1
Design of gas mixer for wink of knowledge test
Figure 1 – Design of gas mixer

Results

In order to better assess the results of the measurements, the mean values of density, pressure, temperature, and reference density (at T = 0 °C, p = 1.01325 bar abs) were calculated.
For this purpose 100 measuring points per medium were used in the steady state.
Figure 2 shows the reaction time and stability of the measured values as well as the reference density output by DGF-I1 and the calculated reference density at 0 °C under atmospheric pressure of 1.01325 bar abs.

 

  1. Reference density Air – dry air
  2. Reference density N2 – nitrogen

A. Data extract table A

B. Data extract Table B

The maximum deviation of the DGF-I1 (density: <0.1 kg/m³) is clearly outside the scale of Figure 2
Table 1 - Mean values of the readings
Table 1 – Calculation of mean values and reference density
Wink of knowledge_air and N2_graphic
Figure 2 – Measurement results for air and N2
Figures 3 and 4 show the frequency distributions of the measured reference densities and help to visualise the repeatability of the gas density sensor.
The same readings were used as for the mean value calculations; the class width was defined as 0.001 kg/m³ for both media.
Figure 1 - Distribution of reference density - N2 nitrogen
Figure 3 – Distribution of reference density – Air dry air
Figure 2 - Distribution of reference density - Air dry air
Figure 4 – Distribution of reference density – N2 nitrogen
The fields A and B marked in Figure 2 show the origin of the raw data of tables A (second 5…15) and table B (second 160…170).
Wink of knowledge_air and N2_cutout Table A
Table A – Measurement results air and N2 – second 5..15
Wink of knowledge_air and N2_cutout Table B
Table B – Measurement results air and N2 – second 160..170

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