A large, enclosed, arena-like structure is used for testing heavy construction vehicles. The facility has high ceilings [>50 feet (15.2 m)] to accommodate the large vehicles. Carbon monoxide must be monitored to both protect the employees, and to control ventilation—via a building management system.
The customer wanted the air to be sampled near the ceiling, close to the ducting. While CO, with a molecular weight of 28.01 is slightly lighter than air at 28.97, proximity to the ducting (close to air intakes, sampling the the most stale air) was the main reason.
The ventilation of the facility is divided into eight zones, and the recommendation was made to sample air at four points in each zone. The resultant 32 points are monitored on a continuous basis.
Given the inconvenient location of the sample points, as well as the presence of diesel smoke under certain conditions, remote diffusion sensors were ruled out. Instead, a sample-draw approach was employed. However, just as calibrating and maintaining sensor heads 50 ft (15.2 m) up in the air is impractical, so would be changing end-of-line sample filters at that height.
Thus, in a departure from the normal sample-draw system, open-ended tubing runs for the 32 sample points terminate near the ceiling at the appointed spots, and extend back to a cabinet at ground level. In this cabinet are all the pumps, as well as the in-line filters dedicated to each sampling point. Each sample line is also provided with a customer-adjustable blowback (backflush) feature, to clean out the sample lines periodically with instrument air.
A second enclosure houses the CO sensors and controls, including the PLC (programmable logic controller), the 32 flow controllers, and the HMI (human machine interface) touchscreen. All user control of the system, as well as alarm and fault display, is at this touchscreen—which includes a comprehensive context-sensitive HELP library.
The system is also provided with a remote annunciator screen, displaying all important system parameters, such as CO concentration and alarm status at each point, as well as any system faults. A limited number of control features can be accessed here.
Arc-Max® data acquisition, archiving, and reporting rounds out the system features.
We believe that this installation embodies the most extensive use of factory automation ever seen in a toxic gas detection system.
For further information on this system, including excerpts from the instruction manual, please contact us.