CO2 Gas Analyzer Overview

PP Systems specializes in the design and manufacture of CO2 infrared gas analyzers (IRGA's). These instruments are single channel, absolute CO2 analyzers for measurement of a single gas stream.  All analyzers are based on a standard module (SBA-4) which employs a non-dispersive measurement technique, coupled with microprocessor based signal processing to achieve good stability and specificity to CO2. All analyzers are fully compensated for temperature and pressure. Fast warm-up, adaptation to changing ambient conditions and excellent stability is achieved by automatic resetting of the analyzer zero at regular intervals.

Normal operation of the analyzers requires a continuous flow of the sample gas. However, static measurements are available with the SBA-4 and EGM-4 enabling the use of aerosol calibration mixtures as well as the injection of syringe samples. All analyzers feature an analog output making them compatible with industry standard PID controllers when CO2 control is required. In addition, all analyzers feature a 4-20 mA current output and digital (RS232) output for transfer of data in ASCII format.

In addition, we offer a full range of soil and canopy chambers (soil CO2 flux, net canopy CO2 flux, etc.) and environmental probes for use with our CO2 infrared gas analyzers to enhance measurement capability. Currently, we offer probes and sensors capable of measuring PAR (Photosynthetically Active Radiation), %RH, temperature and O2.

Auto-Zero

All PP Systems' CO2 infra-red gas analyzers feature the auto-zero facility. This feature, which occurs at regular intervals, allows for fast warm-up, adaptation to changing ambient conditions and excellent stability of the CO2 signal. The action of auto zeroing minimizes the effects on span (gas sensitivity) of sample cell contamination, source aging, changes in detector sensitivity and changes in pre-amplifier gain.

Our company considered using a 2 wavelength detector several years ago, but concluded that true auto zero instruments such as ours provided greater stability and reliability for the following reasons:

• Major effects of temperature are on the transmission characteristics of the interference filters and in 2 wavelength instruments, these are required to closely track.
• Dirt in the cells, changes in cell reflectivity, changes in source position or relative emission over the source surface can differentially affect the sensors.
• Changes in source temperature will affect the relative emissions at the two wavelengths.
• Cross sensitivity problems to other gases are increased as neither wavelength must be affected.
• Both sensors will require electronics and these must have identical temperature coefficients and must age exactly the same.
• Reliability must decline as the component count increases.
• Using two sensors degrades the signal/noise which is inversely proportional to the sensor area.

The only disadvantages to the auto zero approach is that the analyzer requires a flow, a solenoid valve and a chemical absorber (soda lime) which requires replacing at regular intervals. The advantages of an auto-zero system, in our opinion, far outweigh the disadvantages.

Software

All PP Systems' analyzers are supplied with a Windows^® based software program for transferring and logging sensor data. The sensor data may be recorded manually or automatically depending on user specified settings. Stored records (ASCII) can be later imported into your favorite spreadsheet program for further analysis.

On-line help is available to guide you every step of the way.