The Walchem WDP410-1NNU controller is now obsolete and the closest equivalent is the WPH600PSSNN-NN controller. The new WPH600 series has upgraded features; for reference, here is the description of the old model:
pH/ORP controller, with 4 powered on/off relays & 1 powered dedicated alarm relay, 120 VAC, prewired, 6” pigtails to powered relays, no 4-20 mA output, no electrode, integrated datalogging and config file import/export via USB flash stick.