The Walchem WDB400-1NNU controller is now obsolete and the closest equivalent is the WBL600 controller. The new WBL600 series has upgraded features; for reference, here is the description of the old model:
Dual boiler controller, 120 VAC, prewired, no 4-20 mA output, no electrodes, integrated datalogging and config file import/export via USB flash stick.