The Walchem WDIS410-5N1U 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, no 4-20 mA output, free chlorine/bromine sensor, 0-20 ppm, w/flow cell and 20 ft. cable, integrated datalogging and config file import/export via USB flash stick.