The Walchem WDIS series controller is now obsolete and has been replaced by the WDS600 series controller. The new series has upgraded features; for reference, here is the description of the old series:
Disinfection Controller
Control: 2 powered relays, 2 dry contacts
Output: 4-20mA
Controller for Disinfection Process. Optionally includes sensor for chlorine dioxide, free chlorine/bromine, ozone or peracetic acid. Up to two analog outputs available.