After spending more than three years in research and development, the first series of Controle Analytique trace nitrogen in argon was born : the K2000. This unit, housed in a large wall-mounted enclosure was first produced for steel industry but soon found its place in the air separation industry. The K2001 was released one year later. The K2001 series was designed specifically to meet the needs of industrial gas cryogenic producers.

Less than ten years ago, the specification required for trace nitrogen in argon, in many locations, was less than 10 ppm. Today, this specification has dropped below the 1 ppm level with the new technology for argon production and purification. The K2001 is meeting this need perfectly with its lowest range of 0-1 ppm with 10 ppb resolution.

The K2001 gained wide acceptance in the industry but was soon faced with a new challenge : the electronic industries had a nitrogen in argon level below 10 ppb. Controle Analytique rose to the challenge and, the K2002 was released this year. With its first range of 0-100 ppb and a sensitivity of .1 ppb or .5 ppb based on the mode in use, the K2002 is the first low cost ppb nitrogen in argon available on the market. User-friendliness is the philosophy behind the concept.

The K2002's main application is argon purifier monitoring. In such purifiers (getter), the first impurities to break through are nitrogen followed by methane. Consequently, by monitoring the nitrogen, the end user has a clearer indication of the purifier's status.

In special cases,the K2002 may be modified to monitor both the methane and nitrogen as one impurity only. Different arrangements are possible. The K2002, for example may execute a reference reading (from another purifier in line with the sample stream) and if the reading difference exceeds a user preset limit, an alarm is generated. The K2002 comes in standard configuration with the following :

Since the introduction of the K2201, we have seen major air separation companies make it a standard for all their new projects. Other companies made the move to replace their existing analyzers (based on ion mobility, silent electric discharge, or chromatography) with the K22001. A brief description of key factors that set the K2001 apart from the competition follows.

There have been mainly three different technologies used since the sixties for online trace nitrogen analysis : ion mobility, silent electric discharge, and thermal conductivity. Thermal conductivity will not be covered below because of its serious lack of sensitivity for this particular application (low ppm level).

Ion Mobility

Ion mobility uses a radio active source (usually around 50 millicuries of tritium). The high-energy beta radiation ionizes some of the gas passing through the cell. The difference in the mobility of the ions of argon and nitrogen which are formed are measured by an electrometer amplifier. The output is fed to an analog readout or an analog-to-digital converter for display.

Ion mobility was more popular in the sixties and seventies than it was in the eighties and less so today. The reason for this his its lack of sensitivity below 2 or 3 ppm and linearity limited to 100 ppm. The detector also reacts to C0₂, CO, H₂, and CH₄, a serious drawback for low-level measurement. It is also very sensitive to flow and pressure variation into the cell. Finally, the paper work and fees involved in the operation of a radio-active based device (waste management) contribute to its decreasing popularity.

Silent Electric Disharge

There were at least three companies manufacturing this type of analyzer for trace nitrogen in argon measurement. There is some variation in their design but the basic concept is still the same.

In the silent electric discharge or SED, the argon flows through a cell made of pyrez with a quartz window. (Different material may also be used). There are two electrodes connected to a high voltage source on each side of this cell (generally a 7.5 KVAC, 60 Hz neon sign transformer). When the power is applied, the argon/nitrogen mixture emits light. The nitrogen emission is isolated with an interference filter and then, transform to an electric signal generally with a photo-multiplier tube.

There are three different types of signal conditionning for this type of analyzer. One use a chopping wheel to modulate the light beam. The signal measured by the photo detector is fed to a tuned amplifier (or filter) whose frequency is the same has the chopping wheel's. The filter's output is rectified and fed to an analog meter or digital readout. The drawback with this method is the noise ; the chopping frequency and pulse of light from the cell are not synchronized. Also, a mechanical chopping wheel always requires periodical maintenance.

Other manufacturers do not use the chopping wheel but they use bandpass filter (tuned amplifier) to twice the frequency of the cell's alternating power supply. We may also find a phase sensitive amplifier, also called lock-in amplifier or sign bit amplifier instead of a bandpass filter. Since the intensity of the emitted signal is low and the signal itself is subject to variations in the main frequency, the result for low-level measurement will therefore range from passable to mediocre.

Also, the ionization process is not constant and ''Spikes'' signals are present. High flow is normally required (>2SCFH) and over time, dirt deposits accumulate inside the cell from the chemical reaction inside the cell (looks like brownish soot). This result in a loss of sensitivity.

Some systems are also subject to what is called the ''phase reversal'' phenomenon : when a high-level of nitrogen is introduced into these instruments, the reading will decrease. Consequently, contaminated argon may in fact be erronously considered as a good product. What a nightmare for a plant manager!

The K2001

The K2001 analyzer is based on a spectroscopic emission cell, which is not a new technique in itself. It is in fact, the frequency, intensity, regulation as well as the coupling technique and focusing (stabilizing) electrodes used to keep the plasma stable that are the main characteristics that make it so sensitive, stable, and reliable.

The cell volume is less than 1 c.c. The power coupling to the cell and the stabilizing electrodes help maintain plasma position and minimize turbulence caused by gas velocity. All this ensures a better penetration of the analyte (N₂) into the plasma zone. The reaction involved into the cell may be described as follows :

This is the action of metastable argon on nitrogen molecules. There is a strong emission of the second positive system of N₂, from the vibrationnal level V¹=0. There is also a charge transfer ionisation/excitation involved caused by the transfer of charge between ions and atoms. Further information on this subject, however, will be found in future editions of the newsletter.

Special attention is paid to the optical system. Each optical filter selected is tested with our spectrometer system before being included in a K2001. We select a filter coating to achieve optimum temperature stability and to avoid moisture-associated problems. This filter is coupled with a lens that focuses the beam of light so as to fix the center wavelength of the filter properly.

The light is then directed to an enhanced photo diode. All these components are mounted in a cartridge to maintain optical path alignement.

The signal conditionning differs in many respects from the competition. The K2001 amplifies the signal by direct-charge transfer. The new K2001 series comes standard with an analog-to-digital resolution of more than 1 part per million (20 bits) compared to the competition's 1 part per 4095 (12 bits). There is no bulky photomultiplier tube (PMT) with high voltage or a chopping wheel. Consequently, you do not have the problems associated with such systems.

The entire system is controlled by a microprocessor. The quality of both parts and assembly makes the K2001 a choice instrument for the air separation industry. It is very popular, for example, in truck-loading stations.

The following features set the K2001 apart from the competition :

User-friendly operator interface :
Built-in diagnosis system ;
Automatic calibration system available ;
RS-232 or RS-485 communication port for data transmission or modem
(a free communication software is include with theses options).
No maintenance required (nor consumable parts) ;
Automatic flow regulation system ;
Typical 10-second response time for rate of change over 90% ;
Three measuring scales : 0-l, 0-10, 0-100 ppm (10 ppb resolution) ;
Exceptional stability (typical drift less than 1% over a month) ;
Automatic or manual scale change ;
Low gas consumption (works with as little as 25 cc/min.) ;
Particle filter ;
Preconditioned stainless steel tubing ;
Every analyzer includes software and data file representing a 24-hour minimum duration performance and drift test.

The K2001 is based on ''PLUG and PLAY'' philosophy. Our products are characterized by their user friendliness. The qualified Controle Analytique Technical Support Team will provide assistance should you require application information, technical support or service. Your call is important to us and as such, we will follow up until customer satisfaction is achieved. Consequently, please contact us should you need a trace nitrogen measurement. We are certain that we can provide you with the best solution for your application. We are so confident in our analyzers performance that we will reimburse you if you are not satisfied. We are proud to say that this situation never happens.


		World Leader in Nitrogen Gas Analyzers