Combustible Gas Detection – upgrade to upper class!

Monitoring the environment for explosive gases most of the time you would be looking for hydrocarbons. It is a characteristic of hydrocarbons that they have a number of C - H bonds. These bonds absorb infrared light at a wavelength of 3,4 m ( unsaturated hydrocarbons absorb at 3,3 m ). This effect can be used to reliably detect these substances

The most important advantage is that they are resistant against catalyst poisons and high concentrations. They can even be used in oxygen free atmosphere.

Another important advantage of this technology is that a failure cannot go unnoticed. If an important component such as lamp or detector fails, the system will recognise this as 100 % absorption (an alarm situation). Most infrared gas detectors are designed as so - called NDIR (Non Dispersive Infra Red) double- beam detectors. This means, the light beam is divided in two portions with different wavelengthes. One is the measuring beam that will be absorbed by gas, the other is a reference beam at a wavelength that will not be absorbed by gas. This beam compensates for intensity variations of the lamp, dirt and corrosion. As the optics takes are mostly self maintained an eventual inspection only checks if there is gas access to the sensor. Therefore much longer maintenance interval compared to the catalytic sensor can be justified. As a rule of thumb, twice as long is OK.

Infrared gas detection is not restricted to the 0 - 100 % LEL range. Substances with more C - H bonds will absorb more light and thus generate a stronger signal. So fuels and solvents can even be detected in the ppm range. Therefore infrared sensors can also be used for other applications such as TLV monitoring, leakage alert systems, active carbon filter break-through or monitoring of the hydrocarbon content of afterburner air supply.

The signal created by an infrared gas sensor is not linear and strongly temperature dependent. To convert this signal into a standard format that can be handled by a pcs system, it takes a powerful electronics and software package. Having this on board, it is easy to provide more features making the users life easier. Examples are: Non intrusive one- man calibration, included gas library where you select the gas and measuring range you want, display on site, stand - alone design etc.

Sure infrared gas detection is upper class and this means more expensive, but this investment pays easily off for a unit focusing on manufacturing and not wanting spend too much capacity on instrumentation maintenance.

Such typical high - end instrument is the Compur 501 IR. Its stainless steel housing (in protection class IP 67) will withstand any weather condition and is nearly undestructible. The instrument itself offers any feature you can think of: Non intrusive one man calibration without the need of a programming terminal, integrated connection box (no extra cost!), intuitive menu, electrical isolation of signal and power supply and many others.

For plants which already have the required combustible gas detection systems there is now a chance for a very cost- effective upgrade: The Statox 501 IR LC!

It consists of an EEx e (enhanced safety) terminal box and a sensor with integrated electronics. This sensor operates at the same supply voltage as a catalytic sensor. Its output signal is also identical to the signal of a catalytic sensor! This new innovative technical approach keeps the price in the same ballpark as catalytic sensors!

To be precise, all the advantages of an infrared gas detector are now available for nearly the same price as a catalytic sensor and existing gas detection systems can now be upgraded without replacing the existing hardware.

Of course the miniaturised chip inside the sensor cannot provide the same powerful electronics and software package as a high- end instrument, but however the new Compur Statox 501 IR LC features the most important advantages of an infrared system. So the next time maintenance is due with your gas detection system check with Compur Monitors. The investment for an upgrade might pay back within one maintenance interval.