Gas detector working principle (Open path)

Most widely usedGas detector are of two types

a)  Open path gas detectors

b)  Closed path gas detectors

apart from this we also use (Electro-chemical principle GD, MOS GD, Catalytic detection GD)

Let us consider open path gas detector

The opecl (optic path eclipse developed by detronics) is an open path IR (Infra Red) gas detection system that provides continuous monitoring of combustible hydrocarbon gas concentration in the range of 0 to 5 LFL metres over a distance of 5 to 120 metres

LFL stands for Lower Explosive Limit per distance and can be calculated from mA as

[{(mA reading-4)/16}*5]=LFL meters

The system consists of two stainless steel modules a transmitter and a receiver along with mounting fixture.opecl installation

Both modules are powered from an external 24 volt dc.The receiver provides the measurement signal output and an internal magnetic calibration switch.  The transmitter houses dual xenon flash lamps. Both modules are installed at approximately the same elevation and must be aligned to point directly at one another. No direct electric connection is required

opecl tra

(a transmitter/receive module look like is as shown above)

Theory of operation

The opecl transmitter module illuminates a direct linear path ending at opecl Rx module.As flammable hydrocarbon gases intersect the light beam between the two modules certain IR(Infra Red) wavelength are absorbed by the gas while other wavelengths are not.The amount of IR absorption is determined by the concentration of the hydrocarbon gas A pair of optical detectors and associated electronics located in the receiver module measures the absorption.

opecl working

The change in the intensity of the absorbed light (active signal) is measured relative to intensity of light at a non absorbed wavelength (reference signal) The microprocessor computes the gas concentration and converts the value into 4 to 20 mA which is then communicated to external control room .The output 4-20 mA corresponds to 0-5 LFL

OPECL is capable of detecting most hydrocarbon gases and vapors including methane, ethane, propane, butane, and propylene. Gas type and other operational parameters are selected via digital communications. The factory calibrated setting is methane.

To learn more about Instrumentation and Control, purchase your copy now

from amazon


23 thoughts on “Gas detector working principle (Open path)

  1. Pingback: My Post till now | Kishore Karuppaswamy

  2. Pingback: All my posts till now | Kishore Karuppaswamy

  3. Pingback: A typical Foundation Field bus wiring diagram | Kishore Karuppaswamy

  4. Pingback: Flow transmitter DP type | Kishore Karuppaswamy

  5. Pingback: Instrumentation related to a motor driven pump | Kishore Karuppaswamy

  6. Pingback: Dampers | Kishore Karuppaswamy

  7. Pingback: Calibration of Temperature transmitter zero trimming | Kishore Karuppaswamy

  8. Pingback: Calibration of siemens sipart PS2 | Kishore Karuppaswamy

  9. Pingback: Temperature transmitter – RTD | Kishore Karuppaswamy

  10. Pingback: Painting Procedure | Kishore Karuppaswamy

  11. Pingback: Instrumentation Cable design specification | Kishore Karuppaswamy

  12. Pingback: Acceptable accuracy ranges of Instruments | Kishore Karuppaswamy

  13. Pingback: Standard Power supply requirements for Instrumentation devices | Kishore Karuppaswamy

  14. Pingback: General design requirements of Instrumentation part 2 | Kishore Karuppaswamy

  15. Pingback: General design requirements of Instrumentation part 3 | Kishore Karuppaswamy

  16. Pingback: AK ENCON ENGINEERING SERVICES | Kishore Karuppaswamy

  17. Pingback: Bastard Esterraj Stephen and MC GSN Raju | Kishore Karuppaswamy

  18. Pingback: Boiler | Kishore Karuppaswamy

  19. Pingback: General design requirements of Instrumentation part 5 | Kishore Karuppaswamy

  20. Pingback: All my posts till now | kishore koduvayur

  21. Pingback: AS-i (Actuator sensor-Interface Protocol) | Kishore Karuppaswamy

  22. Pingback: Profibus | Kishore Karuppaswamy

  23. Pingback: Ultrasonic flow measurement working principle | Kishore Karuppaswamy

Leave a Reply