The Walchem WDP410-52NU controller is now obsolete and the closest equivalent is the WPH600HSSAN-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, two isolated analog (4-20 mA) outputs, no electrode, integrated datalogging and config file import/export via USB flash stick.