The Walchem WDIS410-542U controller is now obsolete and the closest equivalent is the WDS600 controller. The new WDS600 series has upgraded features; for reference, here is the description of the old model:
Disinfection controller, hardwired, cable glands, single isolated analog (4-20 mA) output, chlorine dioxide sensor, 0-20 ppm, w/flow cell and 20 ft. cable, integrated datalogging and config file import/export via USB flash stick.