The 4CM carbon-monoxide sensor was developed to meet the most stringent toxic-gas and mining standards. The 4CM is said to respond 12% faster to CO hazards and recovers in over half the time of the industry average for other sensors. It has a typical t90 response time of 7 s and a recovery time to an indicated level of less than 2 ppm in less than 100 s. The sensor provides excellent accuracy and stability at high and low gas concentrations, meeting EN45544 requirements for uncertainty, typically achieving 1 ppm for zero concentrations, and less than 1% variation at 250, 750 and 1,000 ppm. — City Technology, Des Plaines, Ill.