The Walchem WDP410-5NNU controller is now obsolete and the closest equivalent is the WPH600HSSNN-NN controller. The new WPH600 series has upgraded features; for reference, here is the description of the old model:
pH/ORP controller, with 4 on/off control outputs and diagnostic alarm relay, hardwired, cable glands, no 4-20 mA output, no electrode, integrated datalogging and config file import/export via USB flash stick.