The Walchem WDP410-12NU controller is now obsolete and the closest equivalent is the WPH600PSSAN-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, two isolated analog (4-20 mA) outputs, no electrode, integrated datalogging and config file import/export via USB flash stick.