Halogen uses a unique pH cartridge in its chlorine sensor system. The pH cartridge can withstand 10 bar to -0.7 bar pressures and rapidly wets if allowed to dry out, with its accuracy restored within 3 minutes. HSI is the only company with this type of pH electrode designed with these specifications in an amperometric chlorine analyzer. It does not require calibration for a year or more, and the cartridges last two years.