Photoacoustic gas monitor for measurement without vapour interference

Paul Boughton
The PA4000 Photoacoustic Infrared Gas Monitor, from General Monitors,  provides high-performance gas monitoring while eliminating interference from water vapors, offering a reliable, low maintenance, cost-saving solution in situations where contaminants or interference preclude use of other measurement techniques.

The PA4000 Gas Monitor is designed with an advanced photoacoustic, infrared (IR) sensor to monitor a variety of gases including hydrocarbons, solvents, alcohols, CO2, CO and other dangerous gases.  It is stable and highly selective to the gas of interest and can operate for months with virtually no drift.  

The PA4000 Gas Monitor eliminates a problem common to infrared analyzers: cross-sensitivity to water vapour. It features a proprietary sensing technique that determines the amount of water vapour in the sample and subtracts it from the gas reading.  This technique allows the gas reading to be stable with no compromise to measurement sensitivity.

With a range of 0-1000 ppm depending on the specific configuration, the PA4000 Gas Monitor is accurate to ± 2ppm at 0-100ppm and ± 10 per cent of reading from 100-1000ppm.  

The PA4000 features sensitivity of 2ppm and resolution of 1ppm, with specifications for other ranges dependent on application.  For certain gases, it detects concentrations as low as 0.01ppm.

The PA4000 Gas Monitor is easy to install, operate and maintain.  Most installations are as simple as mounting the instrument, connecting the sample line and powering the unit. In its most common configuration the monitor draws gas samples via an internal pump, which enables the device to monitor areas that are hard to reach. The PA4000 can also be used by delivering a pressurised sample to the unit. In case of blockage by a dirty end-of-line filter or clogged sample line, the instrument alerts operators by producing a fault.

Like traditional gas sensors, the PA4000 Gas Monitor indicates gas concentrations and alarms.  The direct reading display shows the actual gas value as well as any current alarms and diagnostic messages.  The gas monitor is factory pre-calibrated so that it arrives ready to detect a specific gas at a desired range.

The PA4000 Gas Monitor operates over a wide temperature range of 32°F to +122°F (0°C to +50°C) and has a storage temperature range of -67°F to +158°F (-55°C to +70°C).  It has a temperature effect of ±0.3% per degree (°C) of reading and operates at a humidity range of 0-95% relative humidity, non-condensing.

The PA4000 Gas Monitor can be configured to monitor from up to eight remote areas, with standard features including a vacuum fluorescent display, audio alarm and four relays.  The unit can be housed in general purpose, explosion-proof or rack-mount enclosures. It also offers standard 4-20mA and 0-10 V outputs.  The multipoint sequencer option allows expansion of the PA4000 to monitor up to eight locations with the display indicating the monitored location with its corresponding gas concentration.