Gas Detection Sensor Mounting Height and Location Guidelines: It is important to mount the gas detection heads in areas that are most likely to first be exposed to a gas leak, or that are most representative of the gas levels in the area being monitored. Here are some criteria to consider:
Density of the gas: When detecting for LEL levels of gases and vapors, the density of the gas should be considered. Higher density gases such as propane and gasoline are heavier than air and will tend to collect near the floor. For these gases it is best to mount the sensor within inches of the floor. Lower density gases such as hydrogen or natural gas are lighter than air and will tend to collect near the ceiling. For these gases, it is best to install the sensor within inches of the ceiling.
Toxic gases: Where safe breathing levels are the main concern, sensors should be located in the typical breathing zone, which is 4 to 6 feet from the floor. For low ppm level detection, the density of the gas does not matter as the gas will spread out and flow with the normal ventilation in the area.
Ventilation: Consideration should be given as to where ventilation intake and exhaust ducts are located in a room. Sensors should not be located near a duct blowing fresh air into the room, since the air will not be representative of the monitored area. Sensors can be located near a duct that is removing air from the monitored area, since air from the surrounding area will be drawn towards that location.
Leak source: Where are the most likely leak sources of gas in the room? Sensors should be located near where the leak situation might occur. For example, if you have a large room and there is a gas tank or a process involving gases or solvents in one corner of the room, it is important to install the sensors close to the potential leak source(s). If gas could leak from anywhere in the room, or many locations in the room, then it is necessary to monitor the whole room.
How much area does one sensor cover? A sensor is like your nose, meaning it can only sense what immediately surrounds it. The trick is to strategically place the sensors to detect the gas leak, using the techniques listed above. For a large, open area, an industry rule of thumb is to space sensors 30-40 feet apart. This can be more or less depending on the area to be monitored and the budget.
Height locations for typical gases or vapors:
| Lighter than air% LEL% / % Vol. |
(On or near the ceiling)
|Hydrogen (H2) |
|Breathing Zone PPM |
(4-6ft above floor)
|Acetylene (C2H2), Ammonia (NH3) ppm, Carbon Dioxide (CO2) ppm, Carbon Monoxide (CO), Chlorine (Cl2), Ethylene (C2H4), Formaldehyde (CH2O), Fluorine (F2), Hydrogen Chloride (HCl), Hydrogen Cyanide (HCN), Hydrogen Fluoride (HF), Hydrogen Sulfide (H2S), Methanol (CH4O), Oxygen (O2), Ozone (O3), Nitric Oxide (NO), Nitrogen Dioxide (NO2), Phosphine (PH3), Silane (SiH4), Sulphur Dioxide (SO2), TVOC (target gas dependant)|
|Near The Floor % LEL / % Vol. |
(6 inches above floor)
|Alcohol, Benzene (C6H6), Carbon Dioxide (CO2) %Vol., Diesel Fuel, Ethanol (C2H6O), Gasoline, Hexane (C6H14), Isobutane (i-C4H10), Isobutylene (C4H8), Jet Fuel, Propane (C3H8), Pentane (C5H12), Propylene (C3H6), Refrigerants, Toluene (C7H8), Xylene (C8H10)|
The docking stations for GX-2009, GX-2012, and 03 Series instruments all use the same software to communicate and upload data from the instrument to a data file. This software is called SDM-GX Docking Station PC Controller. You can have one centralized data file on a network location where multiple users can access and review data received from any of these instrument docking stations. As long as the docking stations are connected to a PC (up to 10 docking stations can be connected to one PC) and the PC is connected to the same network where the data file is located, then all instruments can automatically transmit their alarm events, calibration and bump test data to one data file. Anyone who is on the same network and has the SDM-GX software installed on their workstation will have access to all the data coming from these docking stations.
Below is a link to a step by step guide for setting up a network location for a SDM-GX Docking Station PC Controller data file.
How to Create a Network Location for SDM Cal Stations
RKI offers a compact 11” notebook PC with Ethernet and the SDM-GX Docking Station PC Controller software pre-installed as an available accessory to our line of calibration stations. This will allow up to 10 docking stations to be managed.
By definition a confined space is any space that is large enough and so configured that an employee can bodily enter and perform assigned work, has limited or restricted means for entry or exit, and is not designed for continuous employee occupancy. These spaces may include, but are not limited to, underground vaults, tanks, storage bins, pits and diked areas, vessels, sewers, and silos. In addition, this space may not have adequate ventilation or air movement allowing gases to form pockets or stratify within the confined space adding to the danger.
When testing confined spaces prior to entry it is necessary to test at all levels looking for dangerous gases. This may include gases that are lighter than air and may collect at the top of a confined space, such as methane, heavier than air gas that may settle at the bottom of a confined space such as hydrogen sulfide, carbon monoxide which has about the same density as air and oxygen content. Using a sample drawing portable gas monitor for this application makes this task extremely easy to perform. Confined space monitors can be provided with an internal motorized sample pump or an attachable sample pump. An attached pump, either motorized or hand aspirated, can turn a personal portable diffusion monitor into a sample drawing instrument allowing for greater versatility.
For example, if a worker is required to enter a confined space such as a manhole, this individual would need to test the atmosphere around the top of the manhole cover before removing the lid. A confined space safety gas monitor with a sample pump will allow the user to easily “sniff” around the lid for gas. If the manhole lid has pick hole openings, the sample probe can be used to test under the lid for explosive, toxic gas, and oxygen content. Once the lid is removed, the sample probe can then be lowered into the confined space starting at the top and sampling all levels until the probe reaches the bottom.
With a non-sample drawing instrument the sensor block or the monitor itself is lowered into the confined space. The dangers of using a monitor in this fashion is that it can be dropped into liquids destroying the sensors or the instrument. Also, if the monitor is lowered into the confined space, the user would be unable to see the actual gas readings at the various levels. Monitors provided with sample pumps include hoses that can be purchased in various lengths to accommodate a variety of confined spaces. In addition, each monitor can include a probe with water-blocking filter to prevent damage to the instrument in the event that the probe is dropped into liquids.
In summary, choosing a monitor with either internal motorized pump or a diffusion monitor with attachable pump will allow the instrument to be used in a variety of different applications including confined space entry where accurate sampling of the atmosphere is essential to worker safety.
All portable gas monitors need to be calibrated periodically to ensure proper operation. The RKI GX-2003 Model has a feature that allows the user to program a calibration interval that fits their needs, type of usage, and company practice. With this feature, the instrument operator will be prompted each time the instrument is turned on with a calibration status message. If the calibration is still current, the message will indicate the number of days remaining until the next calibration date. If the calibration is overdue, a reminder message will be displayed indicating that the calibration is past due. The calibration date is reset automatically when a successful calibration is performed for all active sensors. If it appears that the calibration date is not being reset properly, verify the following:
The calibration date is only reset if all active sensors are successfully calibrated. When an auto calibration is performed, a calibration fail message will be indicated if any of the sensors fail calibration. If this happens, the calibration date will not be reset.
If the single calibration method is used (calibrating sensors one by one), all sensors must be calibrated successfully for the calibration date to be reset.
Some versions of the GX-2003 include a high range (0-100 % volume) methane sensor. This sensor must be calibrated by the single calibration method, using a cylinder of methane with a high concentration of methane, typically 50 % volume or 100 % volume. In addition, all other sensors must be successfully calibrated using either the auto calibration or single calibration method (see 1 and 2 above).
We hope this information will help to diagnose situations where the calibration date does not appear to be resetting properly. Please contact RKI technical support at 1-800-754-5165, or through our contact page for additional assistance.
Did you know leak detection of hydrocarbons is required at many injection, disposal, and storage wells, compressor sites, and around brine pits? The Railroad Commission of Texas (RRC) statewide rules 95, 96, and 97 outline the requirements for installation and operation of LEL leak detectors. Fixed Systems
The RKI M2 is an ideal solution for meeting these requirements. The M2 transmitter can operate as an independent, stand-alone detector head or with a RKI controller. A digital display of the gas concentration, as well as alarm and status lights, can be viewed through the front window. The M2 also has two levels of alarms with relays, plus a fail alarm with relay.
The RRC rules state the detector needs to be tested twice a calendar year. Calibration of the M2 can be performed by one person utilizing the magnetic wand. Since the housing does not need to be opened, it is unnecessary to declassify the area for maintenance.
Depending on the size of the site, it may be necessary to install multiple LEL detector heads. With our Beacon controller line we can accommodate 1, 2, 4 or 8 points of detection. Or the M2 can operate as a standalone either 24VDC or 12 VD powered.
In environments with combustible gas hazards, it is important to know long before the gas concentration reaches the LEL. Typical safety standards require that a gas detection unit give warnings at 10 – 20% of the LEL. Do not confuse the alarm level with the volume of gas required to reach the LEL. For example: Methane has an LEL of 5% by volume in air. For a gas detector to give an alarm at 10% of the LEL, it must trigger when it detects 0.5% by volume. The detector for this application would most likely be calibrated for the range from 0% to 5% gas by volume, but display the reading as 0 – 100% LEL
You can receive a calibration certificate with any instrument order, if you request it at the time you place your order. Calibration certificates are $10 each. Just reference part # 90-CALCERT as a separate line item of your order.
As an ISO 9001 company, shipping quality products is a major priority for RKI. Each RKI product is put through a detailed quality assurance check-list prior to shipping. RKI includes a Statement of Quality and Conformance card with each instrument to verify this quality process.
For customers who require more detailed calibration information for their instruments, RKI offers a Calibration Certificate. These certificates include the instrument’s model number, part number, and serial number as well as the specific readings during it’s pre-shipment calibration. The certificate also includes traceability information for the gas used.
The GX-2012 can monitor 0 to 100% volume methane when equipped with RKI’s thermal conductive sensor (TE-7561). If the GX-2012 is equipped with both catalytic bead and thermal conductivity sensors, it can monitor and display from 0 to 100% LEL and 0 to 100% volume ranges of methane. The instruments display will show one line for the methane channel and automatically change between % LEL and % volume ranges as the sample changes. There are no set up changes or display mode changes needed.
Also, to help quickly recognize if a worker has been exposed during a particular shift, the GX-2012 has an easy to recognize graphical Peak Reading that can be seen in the normal operation mode. Without going to a different screen or pushing any buttons, a supervisor can quickly recognize if there has been any exposure for the worker while the instrument has been turned on.Add Battery Option letter below to the end of the Base Model part # and add price to the Base Model price.
|72-0290-05-__||GX-2012, 1 sensor, % volume CH4 base, choose battery option|
|72-0290-11-__||GX-2012, 2 sensor, LEL / % volume CH4 base, choose battery option|
|72-0290-13-__||GX-2012, 2 sensor, O2 / % volume CH4 with alkaline battery pack|
|72-0290-18-__||GX-2012, 3 sensor, LEL / % volume CH4 / O2 base, choose battery option|
|72-0290-19-__||GX-2012, 3 sensor, LEL / % volume CH4 / CO base, choose battery option|
|72-0290-23-__||GX-2012, 4 sensor, LEL / % volume CH4 / O2 / CO base, choose battery option|
|72-0290-24-__||GX-2012, 4 sensor, LEL / % volume CH4 / O2 / H2S base, choose battery option|
|72-0290-27-__||GX-2012, 5 sensor, LEL / % volume CH4 / O2 / H2S / CO base, choose battery option|
Deciding on the appropriate and most efficient solution for a fixed system application involves evaluations of the environment and decisions about the different ways to monitor that environment. Typical components of a fixed system include a Controller and a Detector. One decision to make is whether to use a Direct Connect sensor or a Sensor/Transmitter for the detector part of the fixed system. Both Direct Connect Sensors and Sensor/Transmitters have advantages that should be understood before deciding on which detector to select.
Direct Connect Sensors
Direct connect sensors offer the advantage of having a lower cost than a sensor/transmitter style, because a direct connect sensor does not utilize a transmitter in its design. A direct connect style detector can only be used with an RKI controller. The signal-processing circuitry normally found in the transmitter is located in the RKI controller for further signal treatment. In a direct connect configuration, the calibration adjustments are performed at the controller, with the test gas being applied to the sensor. RKI’s controllers utilize unique operating software that allows direct connect sensor calibration to be done quickly and easily by only one person. The distances that a direct connect sensor can be located from the RKI controller are appreciable, ranging up to 1,000 ft. with appropriate sized wire. One other advantage of a direct connect sensor is that it can be calibrated without opening the detector enclosure (also known as ‘non-intrusive calibration’), this can be a big cost savings for detectors located in hazardous locations, as a hot work permit is not required.
Sensor / Transmitters
Detector/transmitters send a feedback signal, usually an industry standard 4-20 mA, with 4 mA being the output at zero (gas free atmosphere) and 20 mA, the output at full scale gas concentration. A mA is a unit of measure for electrical current, one thousandth of an amp. Other digital outputs are also available in various formats, for example ModBus, DeviceNet, Lonworks, etc. There are three primary advantages for choosing a detector/transmitter as supplied by RKI. They are:
It is important to remember that RKI’s Direct Connect detectors are designed and intended to work only with RKI controllers. Also, most of RKI’s controllers can accept either direct connect style or detector transmitter styles. These controllers include the models Beacon 110, Beacon 200 and Beacon 410. The Beacon 800 is designed to operate only with detector/transmitter styles. Also, not every gas detector offering from RKI is available in a direct connect configuration. Please consult with RKI regarding your specific applications.
We hope that the above summary of information helps to clarify the major distinctions between Direct Connect Sensors and Sensor/Transmitters.
*Capable of accepting Direct Connect Sensors
Electrical equipment sometimes must be installed in areas where combustible vapors and gases are used or may be present. These are commonly referred to as “hazardous locations”, and are defined by the National Electrical Code (NEC) in the US, or the Canadian Electrical Code (CEC) in Canada. When equipment must be installed in hazardous locations, there are strict requirements for the construction of the installation, including materials and design requirements. To prevent inadvertent ignition of flammable gases and vapors by electrical equipment, the two most common methods of protection are “Explosion Proof” and “Intrinsically Safe”. We will discuss these methods as they relate to gas detection equipment.
Generally speaking, “explosion proof” is the more commonly used method for detector/sensor assemblies for fixed gas detection systems, where higher voltages and power requirements may be encountered, and the installation is permanent. Intrinsically safe method can also be used for permanent installations where the detector/sensors are relatively low power devices. Almost all portable instruments use the “intrinsically safe” method.
An “explosion proof “ classification for a sensor/transmitter means that the housing has been engineered and constructed to contain a flash or explosion. Such housings are usually made of cast aluminum or stainless steel and are of sufficient mass and strength to safely contain an explosion should flammable gases or vapors penetrate the housing and the internal electronics or wiring cause an ignition. The design must prevent any surface temperatures that could exceed the ignition temperature of the gases or vapors covered by its Group rating (see below). If the sensing element is a high-temperature device (e.g. Catalytic bead or “pellistor”), it may be protected by a flame arrestor to prevent the propagation of high temperature gases to the ambient atmosphere.
An “intrinsically safe” classification and design means that an electronic circuit and it’s wiring will not cause any sparking or arcing and cannot store sufficient energy to ignite a flammable gas or vapor, and cannot produce a surface temperature high enough to cause ignition. Such a design is not explosion proof, nor does it need to be. For permanent installations, such an installation may include “intrinsically safe barriers” that are located outside the hazardous location, and limit the amount of energy available to the device located in the hazardous area.
The North American classifications for hazardous locations as related to flammable gases and vapors:
Class I: Gases and vapors
Division 1: Gases or vapors are usually present and/or may be present at any time in sufficient concentrations for an explosion hazard.
Division 2: Gases or vapors are not normally present and are present only in the event of a leak in some kind of containment vessel or piping, again in potentially hazardous concentrations.
Groups A, B, C, D: Groups of atmospheres categorized by the volatility and/or ignition temperatures. “A” is the most hazardous and “D” is the least hazardous group for gases and vapors.
A typical dilution fitting is a plumbing device that is attached to a gas detection instrument sample inlet port, and then the sample hose is attached to the dilution fitting. When used, the sample flow going into the instrument passes through the dilution fitting. The dilution fitting has 2 small holes; one is in the sample gas stream path, and the second is through the side of the fitting and causes the instrument to take in ambient air. Essentially, the dilution fitting creates a calibrated “leak” into the incoming sample, and dilutes the sample with fresh air. If the dilution fitting is calibrated to be 1 to 1, then when used it will dilute the sample gas stream with an equal amount of ambient air.When is a dilution fitting needed?
There are at least two situations where a dilution fitting is needed. The first common usage is when a catalytic LEL sensor is used to test a space that is inerted (contains no oxygen). Since a catalytic sensor requires oxygen in order to operate, a 1 to 1 dilution fitting blends enough fresh air with the sample to provide enough oxygen for the sensor to properly detect flammable gases if they are present. The second common reason for using a dilution fitting is to extend the range of the gas monitor.
When a dilution fitting is used, it reduces the reading of the gas monitor. If the gas monitor is calibrated to read correctly without the dilution fitting used, then when the fitting is used the gas monitor will read lower than what is actually in the gas sample. For example, if a 1 to 1 dilution fitting is used, since it dilutes the sample by 50%, this means that the reading will be half of what is actually present in the test space. In order to understand what is the correct reading, it is necessary for the operator to multiply the meter reading by 2. If a dilution fitting is 2 parts dilution to 1 part sample, then it knocks the reading down to 1/3 of the actual value, and in this case it is necessary to multiply the meter reading by 3 to get the actual concentration. So, a reading of 50% LEL is actually 150% LEL.
A dilution fitting ratio can be affected by changes in pressure of the incoming gas sample. The fitting is calibrated to provide the correct dilution if the sample is drawn from atmospheric pressure. If the pressure is different, it can change the ratio. For example, if the sample is drawn from a strong vacuum, the fitting may have a difficult time pumping enough gas through the sample hole, and therefore it would draw a larger proportion of the sample through the dilution hole. In this case, you would be getting more dilution of the sample, and so the readings would be lower than expected. If the sample is drawn from a pressurized vessel, it may force too much gas through the sample hole and the pump will not be able to draw the correct amount from the dilution hole. In this case the reading may be higher than expected. In the case where it is testing an inerted space with a catalytic sensor, if insufficient dilution occurs then the LEL reading may be low or near zero because the catalytic sensor is not responding properly due to a lack of oxygen.
Dilution Fittings Increase H2S Range
This special instrument has an internal dilution fitting. It is built inside the instrument to extend the range of the H2S sensor, and the user cannot remove or adjust it. The dilution ratio used is about 7 to 1, but it is not necessary for the operator to do any multiplying because the instrument is designed and calibrated to read correctly with the internal dilution present.
The range of this H2S EAGLE is 0 to 1,000 ppm. It is very important when calibrating this instrument to use a sample bag. Fill the sample bag, and then draw from the bag with the instrument. If a demand flow regulator is used, or if a fixed flow regulator is connected directly to the EAGLE, then the internal dilution will not work properly and the H2S calibration will not be correct.
|EAGLE Configuration|| H2S Range |
|Standard||0 – 100 ppm|
|Internal Dilution Fitting||0 – 1,000 ppm|
|Dilution Fittings||80-0405RK||Dilution fitting 50 / 50, for EAGLE only (for use with hose & probe)|
|80-0406RK||Dilution fitting 3 to 1 for EAGLE only (for use with hose & probe)|
|EAGLE’s with Internal Dilution||72-5101RK-11T||EAGLE for LEL & PPM, with teflon-lined hose, and internal dilution|
|72-5201RK-11||EAGLE for LEL & PPM / O2, with internal dilution for LEL|
|72-5501RK-11||EAGLE for LEL & PPM / O2 / CO / H2S / SO2 (with internal LEL dilution)|
|Transformer Testing EAGLE with Dilution Fitting||72-5101RK-TR1||EAGLE for Hydrogen (H2), 0 – 5% volume, for transformer gas testing, with bag & dilution fitting|
|72-5201RK-TR1||EAGLE for H2 (0-5%)/ O2, for transformer gas testing, with sample bag & dilution fitting|
|Tank Testing EAGLE with Dilution Fitting||72-5101RK-TT||EAGLE for LEL, tank testing version, with float probe & dilution fitting|
|72-5201RK-TT||EAGLE for LEL & PPM / O2, tank testing version, includes float probe assembly and dilution fitting|
|72-5301RK-TT||EAGLE for LEL & PPM / O2 / H2S, tank testing version, includes float probe assembly and dilution fitting|
|72-5401RK-TT||EAGLE for LEL & PPM / O2 / H2S / CO, Tank Tester version (with float probe & dilution fitting)|
Calibration frequency is one of the most commonly asked questions regarding the use of gas detection instruments. Regulatory agencies typically refer users to follow manufacturers recommended protocols for calibration.The calibration frequency for gas detection instruments really depends on the type of use a customer will give the instrument. For example, some users who require the readings to hold up in court as data for certain legal applications must calibrate both before and after each test or each series of tests, in order to remove all doubt of the proper functioning of the instrument. The other extreme is someone who only uses the instrument a couple times a year for non-critical applications. This type of user should calibrate their instrument before each use.
What we generally recommend is that users develop a frequency of calibration that is tailored to their application and usage. Initially, the user may begin by calibrating once per week, and note any changes or adjustments needed to the calibration. If, week after week, there is very little or no adjustment needed, then the calibration frequency can decrease to the point that there will be only a small adjustment needed when calibrating.
In general, for most users, this frequency ends up being somewhere between one and three months. For users who do not wish to develop their own frequency, we recommend that they calibrate once a month.
For users who “bump test” their instrument prior to each use, the calibration cycle can be extended to 3 to 6 months for instruments that successfully pass the bump gas test.
There is no universal standard for pass/fail tolerance on a bump test. The tolerance must be determined by the user based on frequency and usage. A typical tolerance could be +/- 20% or +/- 30%, or a simple triggering of the instrument’s alarm.
All of our newer instruments have auto-calibration. This feature makes calibration quick and painless. Using the 4 gas cylinder, a 4 gas portable monitor can calibrate all 4 channels together in just a minute or two. With this simplification of the calibration task, we encourage users to calibrate their instruments more frequently than they may have done in the past.
Calibration frequency of fixed systems depends upon the type of use you have and the sensor types. Typical calibration frequencies for most applications are between 3 and 6 months, but can be required more often or less often based on your usage.
A precaution to note.
It is generally recommended that a bump test or calibration be performed if it is suspected that the instrument has been subjected to any condition that could have an adverse effect on the unit (sensor poisons, high gas concentrations, extreme temperature, mechanical shock or stress, etc).
Download a PDF of this FAQ
Combustible Gas Detection
In detecting combustible gases in oil and gas, petrochemical and other applications, choosing between the two most common gas sensing technologies used for this purpose will be critical in ensuring a safe, reliable and cost effective solution. These technologies are catalytic combustion and infrared. Both have advantages and disadvantages depending on an application specific needs.
RKI Instruments, a world leader in gas detection equipment, offers both technologies, providing the user with flexibility in selecting the best sensing technology for their situation. Of the many hydrocarbons that are found in industry today, most are detectable with a catalytic combustion sensor and many are detectable with an infrared sensor. It is important to consider the specific compounds to be monitored as there are some that do not readily lend themselves to detection with a general purpose infrared (IR) detector, such as hydrogen, acetylene, and aromatic compounds, like benzene and toluene, for example. We will look at some common compounds and discuss the basic principles of operation for the two technologies as well as their advantages and disadvantages.
Typical alkane gases monitored
Other alkenes, alcohols, and amines monitored
Catalytic detectors are based upon the principle that when gas oxidizes it produces heat, and the sensor converts the temperature change via a standard Wheatstone Bridge-type circuit to a sensor signal that is proportional to the gas concentration. The sensor components consist of a pair of heating coils (reference and active). The active element is embedded in a catalyst. The reaction takes place on the surface of the catalyst, with combustible gases reacting exothermically with oxygen in the air to raise its temperature. This results in a change of resistance.
There is also a reference element providing an inert reference signal by remaining non-responsive to gas, thereby acting as a stable baseline signal to compensate for environmental changes which would otherwise affect the sensor s temperature.
The major advantages of catalytic detectors:
The limiting factors in catalytic detector technology:
The Infrared (IR) detection method is based upon the absorption of infrared radiation at specific wavelengths as it passes through a volume of gas. Typically two infrared light sources and an infrared light detector measures the intensity of two different wavelengths, one at the absorption wavelength and one outside the absorption wavelength. If a gas intervenes between the source and the detector, the level of radiation falling on the detector is reduced. Gas concentration is determined by comparing the relative values between the two wavelengths. This is a dual beam infrared detector.
Infrared gas detection is based upon the ability of some gases to absorb IR radiation. Many hydrocarbons absorb IR at approximately 3.4 micrometers and in this region H2O and CO2 are relatively transparent. As mentioned earlier, there are some hydrocarbons and other flammable gases that have poor or no response on a general purpose IR sensor. In addition to aromatics and acetylene, hydrogen, ammonia and carbon monoxide also cannot be detected using IR technology with general purpose sensors of 3.4 micron specifications.
The major advantages of IR gas detectors:
The limiting factors in IR technology:
There is clear need for both IR and catalytic detectors in industry. When making a choice, be sure to consider the field environment and the variables in detector design. Life-cycle cost assumptions will not hold true in all environments. The same can be said for detector mean-time-to-repair or failure. Careful analysis of detectors, suppliers and field experience will help you to select the best catalytic or IR detectors for your application.
Calibration is a vital and necessary step to ensuring the proper performance of any gas detector. The calibration process requires use of a known concentration of test gas, also known as span gas or calibration gas. Use of incorrect or expired calibration gas can result in improper calibration. This can result in unsafe operation, as well as improper diagnosis of instrument malfunction. This article will focus on disposable (non-refillable) calibration gas cylinders for both reactive and non-reactive gases.
Reactive Gas Mixtures
Reactive gas mixtures are calibration gas mixtures that include at least one component gas which is classified as reactive. This is a broadly used term for chemicals that have some instability under certain conditions, and may react with certain materials, moisture, oxygen, or other chemicals. Reactive gas mixtures include mixtures containing hydrogen sulfide, chlorine, sulfur dioxide, ammonia, hydrogen chloride, among others. Reactive gas mixtures are generally packaged in a special cylinder made of aluminum and treated (passivated) by a special process to minimize reactivity with the reactive gas. Reactive gas mixtures typically have a shelf life of one year or less. After shelf life has expired, it is likely that the concentration of the reactive gas will either decrease or eventually disappear all together.
Non-reactive Gas Mixtures
Non-reactive gas mixtures are calibration gas mixtures that do not include any reactive gases. This is a broadly used term for chemicals that are stable under most conditions, and are not affected by moisture, oxygen, or other chemicals. Non-reactive gas mixtures include mixtures containing alkane or alkene hydrocarbons (methane, ethane, propane, hexane, isobutylene, etc.), nitrogen, hydrogen, carbon monoxide, carbon dioxide, among others. Non-reactive gas mixtures are generally packaged in a cylinder made of steel. Non-reactive gas mixtures have a shelf life of three years.
Shelf Life For All Cylinders
The shelf life for a cylinder is RKI’s warranty. Below is a guide to the shelf life for RKI gas mixtures. As a general rule, all steel cylinders have a 3 year shelf life while aluminum cylinders range from 6-24 months.
|Cylinder Size||Gas mixtures containing||Shelf life |
|17/34/103 L (steel)||All mixtures||3 years|
|34 AL / 58 AL||H2S/N2||2 years|
|34 AL / 58 AL||LEL/O2/H2S/CO||2 years|
|34 AL / 58 AL||SO2/N2||2 years|
|34 AL / 58 AL||NH3/N2||18 months|
|34 AL / 58 AL||Cl2/N2||9 months|
|34 AL / 58 AL||HCl/N2||1 year|
|34 AL / 58 AL||HCN/N2||18 months|
|34 AL / 58 AL||NO/N2||18 months|
|34 AL / 58 AL||NO2/N2||6 months|
|34 AL / 58 AL||PH3/N2||18 months|
|34 AL / 58 AL||SiH4/N2||1 year|
How Do I Know When My Calibration Gas Cylinder Has Expired?
All RKI Instruments calibration gas cylinders include the statement “Best when used by” followed by month and year. Cylinders should not be used beyond this date.
The primary risk associated with combustible gases and vapors is the possibility of explosions. Explosion, like fire, requires three elements: fuel, Oxygen, and an ignition source. Each combustible gas or vapor will ignite only within a specific range of fuel/Oxygen mixtures. Too little or too much gas will not ignite. These conditions are defined as the Lower Explosive Limit (LEL) and the Upper Explosive Limit (UEL). Any amount of gas between the two limits is explosive. It is important to note that each gas has its own LEL and UEL, as shown in the chart below. The gas concentrations are shown by percent of total volume, with the balance as normal air.
Between these two limits explosions can occur under some conditions, with the maximum explosive energy available at approximately the midpoint. Note that these limits are sometimes referred to as LFL (Lower Flammable Limit) and UFL (Upper Flammable Limit). These limits are empirically determined, and various authorities sometimes quote slightly different figures, based on slightly different experimental procedures.
|Common Combustible Gas LEL’s and UEL’s|
|Isopropyl Alcohol (IPA)||(CH3)2CHOH||2.0%||12.7%|
as Tracer: Has a high sensitivity ppm sensor for detection of natural gas leaks down to 10 ppm in leak check mode. When equipped with the proper sensors, the GasTracer has both barhole and leak check modes available. The Gas Tracer has a version where the charcoal filter is removed from the CO sensor to allow for detection of H2S. The readout is displayed as ppm CO (not H2S), and there is no way to differentiate CO from H2S readings.
GX-2012: Has the capability of H2S detection with a dedicated H2S sensor. With the Gas Tracer, H2S sensor is not available.
There are no standards for placement of O2 sensors, or for gas sensors in general for that matter. Think of the sensors like a smoke detector. The sensor responds to what is immediately around the sensor. In the case of using an oxygen sensor to detect the level of oxygen as it is displaced by another gas, the inert gas has to migrate to the sensor from the source. So, when placing sensors, the following variables must be taken into account.
Each RKI sensor is labeled with a serial number (S/N) in which the first two numerals specify the manufactured date.
Example: Serial Number (S/N): 792D01278AT
Generally, an inert atmosphere is one that contains little or no oxygen and is comprised of mostly non reactive gases. Truly “Inert” atmospheres are usually present intentionally as a result of the oxygen being displaced by an inert gas or other gases.
Inert atmospheres may occur in industrial settings like gas transmission companies, pipelines, cryogenics, power transformers and others. Nitrogen, argon, helium and carbon dioxide are the most common components of inert gas mixtures.
The most common sensor used for combustible gases is a catalytic bead type sensor. This type of sensor requires oxygen to operate. As a result catalytic sensors cannot be used for directly monitoring inert atmospheres.
For inert monitoring applications, RKI offers a dilution fitting with many of it’s sample drawing instruments both portables and fixed, which adds the oxygen to the sample at a controlled rate. A dilution fitting allows the catalytic bead type sensors to be used to monitor combustible gases in an inert atmosphere.
Another technique that can be used is to employ an infrared combustible sensor to monitor for methane or heavy hydrocarbons. Infrared sensors, do not require oxygen to operate and therefore do not need dilution fittings. However, IR sensors cannot be used to monitor for hydrogen and some other flammable gases.
If monitoring for inorganic compounds with electrochemical sensors, most EC sensors require a small amount of oxygen to operate. So, while an EC sensor can detect for inorganic compounds in an oxygen free atmosphere on a very short term and intermittent basis, they cannot be used to continuously monitor in a permanent inert atmosphere.
Finally, oxygen sensors may be used to monitor for the integrity of the inert atmosphere and verify that no oxygen is present within that atmosphere. And oxygen sensors may be used to ensure that an inert atmosphere is not leaking to an outside normal atmosphere, when placed in the normal atmosphere, for worker safety.
Please contact RKI Instruments, Applications Engineering, with any questions or for discussions with your applications.
Available RKI Monitors for Inert Monitoring
The Eagle 2 is capable of monitoring most Volatile Organic Compounds. Two types of PID sensors can be used with the Eagle 2, a low range (0 – 50 ppm) sensor and a high range (0 – 2,000 ppm) sensor. With either the low or high range sensor, the Eagle 2 has a PID Relative Response feature, which enables you to change the PID sensor’s response to a different VOC gas on the fly. The Relative Response feature provides a list of pre-programmed response factors of 17 different VOC’s. You can select from this list of gases, whose response is relative to the configured gas, normally isobutylene, which is programmed into the Eagle 2’s memory. For example, if the PID channel is setup for and calibrated to isobutylene (IBL), you can select isopropyl alcohol (IPA) from a gas list accessible from the PID Relative Response Screen in Display Mode so that the PID channel responds to sampled gas as if it were calibrated to isopropyl alcohol. There is no set up or calibration required.
Use Response Factors For Specific VOC’s
The Eagle 2’s relative response feature includes 16 pre-defined gases and 1 gas that can be user defined using the Eagle 2 Maintenance Data Loader Program. If the target VOC is not on the Eagle 2’s list of 17 pre-programmed Relative Responses, a user can go to RKI’s chart of Response Factors to interpret the readings for the desired target VOC by multiplying the reading with the appropriate response factor. Use the link below to find RKI’s Relative Response Factors. This chart is also located in the Eagle 2’s Operators Manual.
The Eagle and Eagle 2 Portable Gas Monitors were designed with EPA Method 21 in mind. EPA Method 21- Determination of Volatile Organic Compound Leaks, is a test method used for the determination of leaks of VOCs from process equipment. The performance requirements for portable instruments used for this purpose are outlined in Sections 6 and 8 of Method 21. Basic requirements from Method 21 are as follows:
Section 6.1 The VOC instrument detector shall respond to the compounds being processed. Detector types that may meet this requirement include, but are not limited to, catalytic oxidation, flame ionization, infrared absorption, and photoionization.
The Eagle and Eagle 2 use a catalytic oxidation sensor that will respond to virtually all VOCs.
Section 6.2 The instrument shall be capable of measuring the leak definition concentration specified in the regulation.
The range of detection for both the Eagle and Eagle 2 is 0-50,000 parts per million (ppm) for methane, which covers most currently defined or published leak rates.
Section 6.3 The scale of the instrument meter shall be readable to + 2.5 percent of the specified leak definition concentration.
With a minimum resolution of 5 ppm, the Eagle monitors will meet this requirement for leak rates defined as 200 ppm or greater. With optional PID sensor even higher resolution is available.
Section 6.4 The instrument shall be equipped with an electrically driven pump to ensure that a sample is provided to the detector at a constant flow rate. The nominal sample flow rate, as measured at the sample probe tip, shall be 0.10 to 3.0 l/min (0.004 to 0.1 ft3/min)…
The Eagle and Eagle 2 use a high-performance electric pump that samples at a nominal flow rate of approximately 0.7 to 1.0 l/min, and sounds an alarm if the flow rate drops below 0.3 l/min.
Section 6.5 The instrument shall be equipped with a probe or probe extension for sampling not to exceed 6.4 mm (1/4 in) in outside diameter, with a single end opening for admission of sample.
The Eagle and Eagle 2 probe is 1/4 OD, and includes a hydrophobic element to prevent intrusion of water or other liquids into the sample system.
Section 6.6 …The instrument shall, at a minimum, be intrinsically safe for Class I Division 1 conditions, and/or Class II Division 1 conditions, as appropriate…
The Eagle and Eagle 2 are certified to be intrinsically safe for Class I Division 1 Group A, B, C, and D hazardous locations by CSA (Canadian Standards Association.
Section 126.96.36.199 The instrument response factors for each of the individual VOC to be measured shall be less than 10 unless otherwise specified in the applicable regulation…
Response factors for various VOCs can be supplied, and a list of commonly encountered materials is included in the Eagle and Eagle 2 Instruction Manual. None of the published factors is greater than 10, in fact none are greater than 3.
Section 188.8.131.52 The calibration precision shall be equal to or less than 10 percent of the calibration gas value.
The Eagle and Eagle 2 can be calibrated anywhere in its range, and calibration precision is better than 5 % of the span gas value.
Section 184.108.40.206 …measure the time required to attain 90 % of the final stable reading…
Section 220.127.116.11 The instrument response time shall be equal to or less than 30 seconds…
Eagle and Eagle 2 response to 90% of full value is less than 30 seconds.
Note: All information referenced to currently available EPA Method 21 as of January 1, 2003.
A dilution fitting is a plumbing device that is attached to Eagle or Eagle 2 sample inlet port, and then the sample hose is attached to the dilution fitting. When used, the sample flow going into the instrument passes through the dilution fitting. The dilution fitting has 2 small holes; one is in the sample gas stream path, and the second is through the side of the fitting and causes the instrument to take in ambient air. Essentially, the dilution fitting creates a calibrated “leak” into the incoming sample, and dilutes the sample with fresh air. If the dilution fitting is calibrated to be 1 to 1, then when used it will dilute the sample gas stream with an equal amount of ambient air.
When is a dilution fitting needed?
There are at least two situations where a dilution fitting is needed. The first common usage is when a catalytic LEL sensor is used to test a space that is inerted (contains no oxygen). Since a catalytic sensor requires oxygen in order to operate, a 1 to 1 dilution fitting blends enough fresh air with the sample to provide enough oxygen for the sensor to properly detect flammable gases if they are present. The second common reason for using a dilution fitting is to extend the detection range of the gas monitor.
When a dilution fitting is used, it reduces the concentration of the sample gas. If the gas monitor is calibrated to read correctly without the dilution fitting, then when the fitting is used the gas monitor will read lower than what is actually in the gas sample. For example, if a 1 to 1 dilution fitting is used, since it dilutes the sample by 50%, this means that the reading will be half of what is actually present in the test space. In order to calculate the correct reading, it is necessary for the operator to multiply the meter reading by 2. If a dilution fitting is 2 parts dilution to 1 part sample, then it knocks the reading down to 1/3 of the actual value, and in this case it is necessary to multiply the meter reading by 3 to get the actual concentration. So, a reading of 50% LEL is actually 150% LEL.
The dilution fitting ratio will be affected by changes in pressure of the incoming gas sample. The fitting is calibrated to provide the correct dilution if the sample is drawn from atmospheric pressure. If the pressure is different, it will change the ratio. For example, if the sample is drawn from a strong vacuum, the fitting may have a difficult time pumping enough gas through the sample hole, and therefore it would draw a larger proportion of the sample through the dilution hole. In this case, you would be getting more dilution of the sample, and so the readings would be lower than expected. If the sample is drawn from a pressurized vessel, it may force too much gas through the sample hole and the pump will not be able to draw the correct amount from the dilution hole. In this case the reading may be higher than expected. In testing an inerted space with a catalytic sensor, if insufficient dilution occurs then the LEL reading may be low or near zero because the catalytic sensor is not responding properly due to a lack of oxygen. It is also critical to make sure the probe filters are clean as this too can cause erroneous (low) readings. The Eagle and Eagle 2 1:1 dilution fitting can be used with any length hose up to 70 ft. (21m).
The Eagle 2 data-logging capacity is dependent on the interval trend setting, number of sensors installed, and number of alarms or other events.
The following chart of the Eagle 2 data-logging capacity is for an Eagle 2 standard four gas unit with no alarms or events. Additional sensors, alarms or events will reduce the listed data-logging capacity.
|INTERVAL TREND TIME||DATA-LOGGING HOURS|
|5 seconds |
180 seconds (3 minutes)
300 seconds (5 minutes)
600 seconds (10 minutes)
|239 hours (10 days) |
479 hours (20 days)
959 hours (40 days)
1,439 hours (60 days)
2,879 hours (120 days)
8,639 hours (360 days)
14,399 hours (600 days)
28,798 hours (2,000 days)
The Eagle 2 can store the following files in addition to standard interval trend data:
No, you do not need the NiMH batteries in the Eagle 2 for continuous operation mode.
In critical applications, we recommended using fully charged NiMH batteries installed as a power back-up.
It is important to note, not to use the continuous operation adapter or charger with alkaline batteries installed in the Eagle 2. This can result in damage to the instrument.
We also recommend using the continuous operation mode only for short term and infrequent extended monitoring events. Please do not try to use it as a substitute for a fixed gas detection system. When using the Eagle 2 in continuous operation mode, the instrument is no longer intrinsically safe.
The battery charger for Eagle 2 (including power adapter as pictured above) is Part Number; 49-2175RK.