PetroStreet

What's the difference in IR and open path IR detectors and where are they preferred to be installed?

Point IR Detectors

Area Monitored: Point IR detectors monitor a specific, localized area for the presence of flammable hydrocarbon gases or vapors. They are positioned at locations where gas leaks are likely to occur in order to quickly detect dangerous concentrations.
Measurement: They measure the concentration of hydrocarbon gas at a fixed absorption path length, typically a few inches, using infrared absorption of an optical beam.
Output: The output is usually expressed in parts per million (ppm) or percentage of the lower explosive limit (%LEL).

Open Path IR Detectors

Area Monitored: Open path IR gas detectors monitor a wide area along the path of an infrared beam, which can extend up to 130 meters. They are suitable for perimeter monitoring, along pipelines, and around storage tanks.
Measurement: They measure the average gas concentration along the entire beam path, using a broadband IR emitter and alternately selecting active and reference wavelengths.
Output: The gas concentration output is expressed in ppm.meters or LEL.meters, representing the product of the average gas concentration and the gas cloud length. They do not pinpoint the exact location of a leak but rather the total amount of gas along the path.

Some more details, if needed:

Advantages of Open Path IR Detectors

Wide Area Coverage: Effective for monitoring large open areas or perimeters.
High Sensitivity Leak Detection: Offers high sensitivity in detecting leaks.
Low Maintenance: Generally require less maintenance compared to point detectors due to the fewer number of sensors needed to cover large areas.
Fail-to-Safe Detection: Incorporate fail-to-safe detection mechanisms.

Disadvantages of Open Path IR Detectors

Cannot Pinpoint Leak Location: Unable to pinpoint the exact location of a gas leak.
Susceptibility to Environmental Factors: Environmental conditions such as fog, rain, and dust can affect the transmission of the infrared beam, potentially reducing the detector’s accuracy.

Advantages of Point IR Detectors

Precise Location: Can be placed at the known location of the highest gas concentration.
Cost-Effective: Generally less expensive than open-path detectors, making them suitable where localized monitoring is sufficient and cost is a key consideration.

Disadvantages of Point IR Detectors

Limited Coverage: Monitor only a single point, which may not be sufficient for large areas where gas dispersion is unpredictable.
Slower Response in Open Areas: In exposed outdoor locations, weather shields are required, which can increase response time.

Additional Considerations

Applications: Open path detectors are suitable for situations where gas release is dispersed by wind or natural diffusion. Point detectors are better for monitoring specific potential leak sources.
Cost: Open path detectors usually cost more than single point detectors, but can be more cost-effective than using a row of point detectors to achieve the same coverage.
Maintenance: Open path IR detectors generally require less frequent maintenance than point detectors.

ivani1, excellent explanation.
Got that on for one of my support works.

Point Type IR Detectors:
Point type detectors shall be specified for the following applications:
a. Locations having inert gas backgrounds
IR detectors can be used in locations that have inert gas backgrounds because such detectors do not require oxygen to operate.
b. Locations having constant background of gases
IR detectors are not poisoned by a constant background of gases and do not respond to hydrogen.
c. If specific gases require detection
IR detectors can be tuned to detect somewhat specific gases because they measure different hydrocarbons at specific wavelengths.

Open Path IR Detectors:
1.The installation of an open path type IR systems shall not be installed without prior approval of the owner.
2.Open path IR detectors shall not be used in congested areas or in areas of high traffic.
3.The IR source and reflector shall be installed on a rigid structure to prevent movement caused by ambient atmospheric changes.

Much appreciated.
We as Operations Support staff need many such short & correct explanations about things.

tuan wrote: 22 Jul 2025, 18:40 Point Type IR Detectors:
Point type detectors shall be specified for the following applications:
a. Locations having inert gas backgrounds
IR detectors can be used in locations that have inert gas backgrounds because such detectors do not require oxygen to operate.
b. Locations having constant background of gases
IR detectors are not poisoned by a constant background of gases and do not respond to hydrogen.
c. If specific gases require detection
IR detectors can be tuned to detect somewhat specific gases because they measure different hydrocarbons at specific wavelengths.

Open Path IR Detectors:
1.The installation of an open path type IR systems shall not be installed without prior approval of the owner.
2.Open path IR detectors shall not be used in congested areas or in areas of high traffic.
3.The IR source and reflector shall be installed on a rigid structure to prevent movement caused by ambient atmospheric changes.