Calibration Basics for Gas Density Applications

Choosing Calibration Gasses

Whether you use Yokogawa's GD system to measure gas density, specific gravity, or % concentration, at its core it is always measuring DENSITY. Below are a few tips for choosing calibration gasses for these applications:

  • Remember that the system is only measuring density. Choose calibration gasses (Zero and Span) whose densities bracket your normal measuring density.
  • Calibrating with two gasses (Zero Gas and Span Gas) is the preferred method and results in the most accurate measurements.
  • If the density of your application does not vary widely, it is acceptable to calibrate with one gas that has a density similar to your normal process value.
  • The GD system provides excellent measurement linearity. Because of this, you can choose inexpensive, safe calibration gasses. For exampl e, the density of Acetylene may be exactly what you need in a calibration gas for your application, but do you really want to store that flammable of a gas? If not, you can choose a safer gas like Helium, whose density may not be as desirable, but will still provide accura te measurements because of the GD's linearity.
  • Locate the calibration gas bottles close to the GD40 detector. This will decrease calibration time and reduce calibration gas consumption.
  • Only use "Calibration Grade" gasses with certifi ed purity. Do NOT use bulk gasses as they will introduce measurement error. Custom blended gasses are not required.

*See the appendix for common gasses and their densities.

Setting up the GD for your Calibration Gasses

To set calibration data, press the【*】key in the measurement mode, (when password is selected, enter the password (XXX) ) and select the parameter『*CAL.DT』

Zero-point density『*Z_DNS』: Enter the density of your zero cal gas.
Configurable range = 0.0000 to 6.0000 (kg/m3) or 0.00000 to 0.40000 (lb/ft3)

Span-point density『*S_DNS』: Enter the density of you span cal gas.
Configurable range = 0.0000 to 6.0000 (kg/m3) or 0.00000 to 0.40000 (lb/ft3)

Output during calibration『*C_HLD』: Do you want the analog output to be held during calibration?

  • Disable: 0
  • Enable: 1
  • Enable (preset value): 2

Performing a Calibration

The majority of applications will require a manual calibration. The steps for completing the calibration are as follows:

  1. Press the "MODE" key.
  2. Press "NO" when DISP is displayed.
  3. Press "NO" when SEM CAL is displayed.
  4. Press "YES" when MAN CAL is displayed.
  5. Press "YES" when ZERO is displayed.
  6. Confirm that the correct density is displayed for your zero calibration gas.
  7. Flow your zero calibration gas at a rate of 0.6 LPM to the GD40 detector. This should be similar to your process gas flow rate.
  8. Press the "Enter" key.
  9. Allow the density reading to stabilize. Once stable, press the "Enter" key.
  10. Press "YES" when SPAN is displayed.
  11. Confirm that the correct density is displayed for your span calibration gas.
  12. Flow your span calibration gas at a rate of 0.6 LPM to the GD40 detector.
  13. Press the "Enter" key.
  14. Allow the density reading to stabilize. Once stable, press the "Enter" key.
  15. Return the process gas flow back to the detector.

Appendix

Table 1 Pure Gas Specific Gravities, Color Caloific Values, Densities and Net Calorific Values (0 °C, 1 atm)

No. Gas Chemical formula Specific gravity (Air=1.0000) Gloss Calorific value (kJ/m3) Gas Density (*) (kg/m3) Net Calorific Values (K/Jm3)
1 Carbon monoxide CO 0.967 12610 1.2504 12610
2 Hydrogen H2 0.0696 12780 0.08988 10830
3 Methane CH4 0.554 39940 0.7175 36020
4 Ethane C2H6 1.038 70470 1.3552 64550
5

Ethylene

C2H4 0.968 63560 1.2612 59620
6 Propane C3H8 1.522 101400 2.0102 93390
7 Propylene C3H6 1.452 93730 1.9122 87760
8 n-Butane n-C4H10 2.006 134300 2.7024 124100
9 i-Brutane i-C4H10 2.006 133100 2.6897 122900
10 1-Butene 1-C4H8 1.936 126300 2.5956 118100
11 cis-2 Butene cis-2-C4H8 1.936 126600 2.6042 118400
12 trans-2 Butene tr-2-C4H8 1.936 126300 2.6042 118100
13 i-Butene i-C4H8 1.936 125500 2.5933 117400
14 n-Pentane n-C5H12 2.490 171400 3.4542 158700
15 i-Pentane i-C5H12 2.490 169300 3.4266 156800
16 n-Hexane n-C6H14 2.974 215700 4.3205 199900
17 Benzene C6H6 2.695 163300 3.8343 156800
18 Toluene C6H5CH3 3.179 22770 4.8495 217600
19 Carbon dioxide CO2 1.519 1.9771
20 Oxygen O2 1.104 1.4289
21 Nitrogen N2 0.967 1.2504

Source: JIS K2301-1992
(*) Gas density is only reference data.

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