Fast Response
Modern process control requires fast response without overshoot. The Oxigraf Process Controller responds in less than a second. The transit time of the gas sample through the sampling tube may be 1 second per meter of sampling tube. To respond within 5 seconds, a monitor with a 1 second response time would need to be placed within 4 meters of the potential hazard. Electrochemical sensors may incorporate long averaging times, 20 or more seconds, for large, abrupt changes in oxygen concentration. Laser diode technology offers short response times to meet your control requirements.

Sample Flow Monitor
The Oxigraf O2iL includes a sampling pump, hydrophobic filter, and flow sensor. The microprocessor controller maintains the flow at a constant value. Any flow blockage or pump failure is reported as a low flow fault. Filter impedance can also be measured to indicate a need for filter maintenance. Thus remote monitoring of the flow system is enabled. Pumps are available to provide sampling at atmospheres down to 200 mTorr.

Temperature, Pressure, and Humidity
An error budget must be established for oxygen process control. Humidity changes can cause a large variation in the oxygen measurement. A hot, wet day relative humidity of 50% at 37°C (99°F) corresponds to an absolute humidity of 3.2%. Such a water vapor dilution would cause a variation from the cold, dry air oxygen concentration of 20.9 to 20.2%, a change of 0.7%. If 19.5% is to be the alarm value, then variations from all other sources must be substantially less than 0.7% (the difference between 19.5 and 20.2%).
    Therefore, temperature and pressure corrections are important. An oxygen sensor which measures oxygen partial pressure instead of concentration would report an oxygen variation of 2% with a 10% variation in barometric pressure. The Oxigraf sensor is corrected to within ±0.2% over pressure changes of 50% and temperature changes from 0 to 50°C.

Available Factory Installed Options for the O2iL

Remote Display and Remote Maintenance
The Oxigraf Process Controller includes various communication outputs of oxygen concentration, alarms, flow, and system status. It is essential for cost effective process control to have both local and remote indication of process control operation. Another advantage of a remote display we call “remote maintenance”. A major cost of oxygen process controllers is the requirement for periodic maintenance and recalibration. With remote maintenance, site service and recalibration are no longer required to be periodic. Any system, power, flow or measurement faults will be flagged on a remote display, and service and calibration can be performed on an as-needed basis. For example, choosing an average oxygen concentration in humid air of 20.7%, the central monitor might flag measurements outside a range from 20.2 to 21.2% as requiring a calibration visit; with such a remote maintenance protocol, a periodic calibration frequency might be annual or less frequent.

Tunable Diode Laser Spectroscopy
The Oxigraf O2iL is the next generation oxygen process controller. Laser diode absorption spectroscopy assures stable, long-life oxygen measurement: there are no electrochemical cells to replace or paramagnetic sensors to recalibrate. The laser diode, derived from high reliability telecommunications VCSEL (vertical cavity surface emitting laser) diode technology, is rated for more than 100,000 hours mean time to failure. The laser diode is thermally and electronically tuned to measure the absorption of oxygen at 763 nm, and also periodically measures the background to provide an automated zero. Pressure and temperature corrections are made to yield the correct oxygen concentration as the weather changes.

Insensitivity to Movement
The Oxigraf technology has no moving parts, in contrast to paramagnetic technology. Laser diode technology will have no false alarms due to equipment vibration, mechanical accidents, or even earthquakes.

Code Access
Control of the unit via the 12-key capacitive-touch panel can be restricted by use of a password. This permits access control for maintenance and unit calibration.