Infrared optical gas-measuring device and gas-measuring process

• US 6,583,417 B2
• Filed: 02/01/2001
• Issued: 06/24/2003
• Est. Priority Date: 02/10/2000
• Status: Expired due to Fees

• Current Assignee: Dräger Sicherheitstechnik GmbH (FPS Vermögensverwaltung GmbH)
• Original Assignee: Dräger Sicherheitstechnik GmbH (FPS Vermögensverwaltung GmbH)
• Inventors: Stock, Burkhard
• Primary Examiner(s): Porta, David
• Assistant Examiner(s): Sung, Christine
• Application Number:
  US09/773,721
• Publication Number:
  US 20010015408A1
• Time in Patent Office: 873 Days
• Field of Search: 250/338.5, 250/339.07, 250/339.08, 250/343, 250/339.02, 250/339.09, 250/339.13, 250/338.3, 250/339.06, 73/190.1, 73/232, 356/437
• US Class Current: 250/338.5
• CPC Class Codes: G01N 2021/3166 using separate detectors and filters
• CPC Class Codes: G01N 21/314 with comparison of measurements at specific and non-specific wavelengths dual wavelength spectrometry G01J3/427
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

An improved gas-measuring device and a gas-measuring process is provided for determining the concentration of a gas by infrared absorption. The improvement is the compact design of the gas-measuring device and the higher reliability of the measurement results furnished by the gas-measuring device and the gas-measuring process. The gas-measuring device has an infrared radiation source (1), a pyramid-like beam splitter (7), and a quadrant detector, which has two measuring detectors (3, 4) and two reference detectors (5, 6). This guarantees a compact design of the gas-measuring device and, as a consequence, low fault liability of the measurement. The gas-measuring process includes an advantageous evaluation of the measuring signals (M1, M2) received by the two measuring detectors (3, 4) and of the measuring signals (R1, R2) received by the two reference detectors (5, 6). The plurality of the measuring signals (M1, M2, R1, R2) and the manner of their evaluation leads to a more reliable determination of the gas concentration.

Claims

1. A gas-measuring device for determining the concentration of a gas, comprising:

an infrared radiation source sending measuring signals;

a quadrant radiation detector for infrared absorption of the measuring signal comprising four individual detectors arranged in a square pattern, a pyramid-like beam splitter dividing the measuring signals of the infrared radiation source among said four individual detectors, said four individual detectors including two measuring detectors located opposite one another and equipped with first identical infrared filters and two reference detectors located opposite one another, and equipped with second identical infrared filters.

2. A gas-measuring device in accordance with claim 1, wherein said four individual detectors are pyroelectric detectors.

3. A gas-measuring device in accordance with claim 1, wherein said detectors determine concentration of methane.

4. A gas-measuring device in accordance with claim 1, wherein the transmission range of the infrared filters is 3.3±

0.1 μ

m.

5. A gas-measuring device in accordance with claim 1, wherein the transmission range of the infrared filters is (3.9±

0.1) μ

m.

6. A gas-measuring device in accordance with claim 1, further comprising:

a processor for forming the quotients $\mathrm{Q1}=\frac{\mathrm{M1}}{\mathrm{R1}},\mathrm{Q2}=\frac{\mathrm{M1}}{\mathrm{R2}},\mathrm{Q3}=\frac{\mathrm{M2}}{\mathrm{R1}},\mathrm{Q4}=\frac{\mathrm{M2}}{\mathrm{R2}},$

from the measured signals M1, M2 received by the measuring detectors and the reference signals R1, R2 received by the reference detectors and using the formed quotients to determine the gas concentration.

7. A gas-measuring device in accordance with claim 6, wherein:

said processor averages all four formed quotients to determine the gas concentration.

8. A gas-measuring process for determining the concentration of a gas by the infrared absorption of the measuring signals sent by an infrared radiation source and received by a quadrant detector comprising two measuring detectors and two reference detectors, the process comprising the steps of:

forming the quotients $\mathrm{Q1}=\frac{\mathrm{M1}}{\mathrm{R1}},\mathrm{Q2}=\frac{\mathrm{M1}}{\mathrm{R2}},\mathrm{Q3}=\frac{\mathrm{M2}}{\mathrm{R1}},\mathrm{Q4}=\frac{\mathrm{M2}}{\mathrm{R2}},$

from the measured signals M1, M2 received by the measuring detectors and the reference signals R1, R2 received by the reference detectors; and

using the formed quotients to determine the gas concentration.

9. A gas-measuring process in accordance with claim 8, wherein the gas concentrations $\mathrm{C1}=\frac{\mathrm{Q°}}{}$

1-Q1Q°

1·

Cal1,C2=Q°

2-Q2Q°

2·

Cal2,

C3=Q°

3-Q3Q°

3·

Cal3,C4=Q°

4-Q4Q°

4·

Cal4.

are obtained from the quotients Q1, Q2, Q3, Q4 by standardization, wherein the quotients Q°

1, Q°

2, Q°

3, Q°

4 are related to a zero gas measurement and Cal 1, Cal 2, Cal 3, Cal 4 are calibration factors, which are determined by the measurement of a reference gas.

10. A gas-measuring process in accordance with claim 9, wherein the gas concentrations C1, C2, C3, C4 are determined continuously or at predetermined time intervals.

11. A gas-measuring process in accordance with claim 9, wherein a value is determined for the median for all values of the gas concentrations C1, C2, C3, C4 within a preset tolerance range, and a warning signal is sent if at least one value of the gas concentrations C1, C2, C3, C4 is outside the preset tolerance range.

12. A gas-measuring process in accordance with claim 9, wherein the mean value C=0.25 (C1+C2+C3+C4)

is formed for all values of the gas concentrations C1, C2, C3, C4 within a preset tolerance range, and a warning signal is sent if at least one value of the gas concentrations C1, C2, C3, C4 is outside the preset tolerance range.

13. A gas-measuring process in accordance with claim 9, wherein clean air or nitrogen is used as the zero gas for the zero gas measurement.

14. A gas-measuring process in accordance with claim 9, wherein methane with a concentration of 40% of the LEL is used as the reference gas.

15. A gas-measuring process in accordance with claim 8, wherein the concentration of methane is determined.

16. A gas-measuring process in accordance with claim 8, wherein:

said using of the formed quotients to determine the gas concentration includes averaging all four formed quotients.