Open-path gas detector monitors with IR beam

New types of infrared (IR) flammable gas detectors from Foxboro offer "complete" coverage. Precision Light Measurement Systems (PLMS) provide a constant stream of detection across long distances. Strategically placed detectors enable crisscrossing a facility with line-of-sight IR beams. Thus, it is almost impossible for a gas cloud to escape detection.

For large areas, a system of beams provides wider coverage than possible with individual point detectors. Open-path systems supply critical data on the severity of the gas release.

The figure shows a spherical tank being monitored using an open-path detection unit. The sensors are positioned 40-ft apart at the sphere's base. Because they are detecting only the fringe at 10% LEG- a significant warning level has not been reached.

In this example, the detector is still in a low gas density area of the cloud, but the detector is able to indicate a significant gas level and provide notice.

When open-path detection is not viable, point IR systems are recommended. Applications include small confined locations, low-lying pits and other areas where gases can collect. These units must operate daily in harsh environments--rain, snow, fog, sleet, dirt and sunlight. These conditions can affect a transmitter's beam ability to reach the receiver. However, a dual detection design incorporates a reference beam, which is invisible to the gas, and identifies when the beam intensity drops.

During a rainstorm, the coincident measurement

beam is affected to the same degree as the reference beam, thus the detector registers no gas. But the detectors will register the presence of a gas when there is an intensity differential between the sample and reference beams.

If sunlight interference is a problem, series GD4022 and GD4024 provide immunity with dual opposed transceivers that operate without interruption.

Open path and point IR units can detect an array of hydrocarbons. Typical gases include propane, methane, butane, isobutylene, methanol, ethyl acetate, ethylene dichloride, MTBE and others. Benefits from these systems are claimed to be: reliability, ease of maintenance, accuracy, durability and ease of calibration.