Archive: Jan 2020

OBOGS Monitoring

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Aircrew hypoxia warning times can be reduced by perfecting laser diode absorption spectroscopy oxygen sensors for OBOGS monitoring.



The onboard oxygen generating system(OBOGS) is an alternative to liquid oxygen (LOX). When compared to a LOX system, the OBOGS has several advantages. First, it’s availability may be as high as 99 percent. There is no requirement for depot-level maintenance. The OBOGS has no daily service requirements, and scheduled preventive maintenance occurs at 2,000 hours. Incorporation of the OBOGS eliminates the need to store and transport LOX. Additionally, it eliminates the need for LOX support equipment. The potential for accidents related to LOX and high-pressure gases is greatly reduced. The basic components of the OBOGS are the concentrator, oxygen monitor, and oxygen breathing regulator. The concentrator produces an oxygen-rich gas by processing engine bleed air through two sieve beds. The oxygen monitor senses the partial pressure of the gas and, if necessary, provides a low-pressure warning to the pilot. The oxygen regulator is a positive pressure regulator.



Pilot Hypoxia:

  • Pilot hypoxia can result in impaired judgment, loss of aircraft, and loss of aircrew.
  • 22 aircrew hypoxia reports investigated by NAWCAD over 2 years.
  • F/A 18C Class A mishap, May 2001, loss of pilot/aircraft, $30M cost of aircraft and site cleanup.


Oxigraf Fast Responding Oxygen Sensors:

  • Reliable VCSELs now make laser diode oxygen sensors viable for air crew OBOGS monitors.
  • Effort can be combined with OBOGS flow/pressure monitor for integrated pilot “dry mask” warning or backup system.
  • LD Sensor fast enough to monitor gas composition blender systems.

Please download your On-Board Oxygen Generating System (OBOGS) Monitoring Application Note (pdf)

Oxygen Depletion Calculator

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The calculation of percentage of oxygen in the air after the evaporation of a volume of liquefied gas – nitrogen or solid CO2 in a confined space.

  • Calculate the volume (Vr m3) of the confined space.
  • Calculate the volume of the released gas (Vg) by multiplying the volume of the liquid nitrogen (in liters) or weight of solid carbon dioxide (in Kg) by the expansion ratio of LN (.682) or the inverse density of CO2 (.552 m3/Kg).
  • Calculate the volume of available oxygen (Vo m3) as 0.2095*(Vr-Vg).
  • Calculate the % oxygen available to breathe as 100*Vo/Vr.
Room Length (meters)
Room Width (meters)
Room Height (meters)
Type of Spill (LN or CO2)
Amount of Spill (liters of LN2 or Kg of CO2)

Volume of Room.

Volume of Released Gas.

Volume of Available Oxygen.

Percent Oxygen Available to Breathe.


  • Uniform mixing of LN or CO2 with room air.
  • No pressure considerations taken.
  • Spill is contained in the room.

Oxygen Monitor for Quantum Computer Helium Laboratory

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Model O2iM – Oxygen Deficiency Safety Monitor:

The Oxigraf state of the art Oxygen Deficiency Monitor, the Model O2iM, is a fast response, accurate and reliable safety monitor for oxygen displacement monitoring in Quantum Computer Laboratory, MRI, NMR, and liquid nitrogen and helium storage facilities. Our reliable solid state sensor does not require routine maintenance or factory calibration, and the O2iM is equipped with an automatic/programmable auto-calibration system. The system easily interfaces with alarm system, HVAC controls, and building management systems.

Oxigraf Case Study:

State-of-the-art helium (and other rare gases) recovery, purification and liquefaction systems are required for operation of helium-3/helium-4 milli Kelvin dilution refrigerators in modern Quantum Computer Laboratories, liquid helium superconducting magnets (such as NMRs, MRIs, etc.), MEG systems for medical applications, cryogenic measurement cryostats, various size helium and cryogenic vacuum facilities.

The Problem:

Reliable solutions for sampling gas from remote locations in a Helium Processing Facility are needed in order to monitor equipment and personnel safety. During their operations, helium processing facilities are dealing with the presence of cryogenic nitrogen and helium, which presents oxygen deficiency hazards. Oxygen deficiency in the workplace can lead to blackouts, cause falls, and present more serious health risks — some of which can be fatal. The Oxigraf expert’s team can be brought in to help eliminate the risk of oxygen depletion.

The Solution:

The Oxigraf Model O2iM, which has a high-flow pump option and allows for sampling from long distances. This sensor allows for continual monitoring of the clients’ facilities atmosphere from a safe location, and provides local alarms and interfaces with sophisticated safety features to prevent hazards such as cryogenic spills, which can lead to rapid displacement of breathing air.

Oxigraf’s top-of-the-line oxygen deficiency monitor is flexible and efficient, and provided the client with a reliable, immediate oxygen alarm for concentrations of less than 19.5%. It also eliminated the need for frequent recalibration or replacement of oxygen sensors, as well as the comprehensive, time-consuming maintenance often involved in sampling systems. The risk of false alarms and alarm failures can also be eliminated.


This unique sensor features a rapid response time of less than a second. The built-in pump draws gas remotely, allowing for these quick response times. In fact, we offer the best response speed/signal in the industry, and can add multiplexors (valving) in order to monitor four or more locations from over 100 feet away.The transit time of the gas sample through the sampling tube may be 1 second per meter of sampling tube with our standard pump or using our high flow option, a much faster response is possible on long tubing lengths. The high flow pump operates at a much faster rate and pre-fetches samples.

Additionally, this sensor is insensitive to movement, temperature and pressure changes, has auto-calibration for absolute accuracy, and includes options for multi-port and high-flow sampling. It also features a remote display and optional battery backup to allow for proper functioning during power interruptions. In addition, it can be fitted with a Z-Purge system, which allows the unit to be used in Class 1 Div 2 hazardous areas. The monitor includes a sampling pump, hydrophobic filter, and flow sensor, while the microprocessor controller maintains the flow at a constant value.

The Result:

When comparing the Oxigraf O2iM sensor to other O2 sensing solutions, it can be determined that O2iM is “the champion,” allowing for reliable performance 24/7. Oxigraf customers are particularly impressed with the unique engineering of the “Pre-Fetch” high-flow pump option, which allows for the monitoring of distant sample locations while maintaining fast response times.

Typical O2iM Installation:

Learn More:

Oxigraf has over 20 years of experience producing laser gas sensors and instruments, and is the leading manufacturer of laser absorption spectroscopy sensors for oxygen gas measurement and analysis. Oxigraf O2iM Oxygen Safety Monitors have been widely adapted in hundreds of facilities since 2004, replacing a wide range of less reliable electrochemical sensors. Oxigraf O2 and CO2 sensors, in particular, have been widely adapted by OEM manufacturers of medical respiratory gas monitors in order to measure breath waveforms, end-tidal gas values, anaerobic thresholds, VO2 maxs, and non-invasive cardiac outputs. For more information on our sensors, or to speak with an expert about your specific monitoring needs, contact the team today.

Please download your Oxigraf Case Study: Oxygen Monitor for Quantum Computer Helium Laboratory