The Walchem WPH420-3NNN controller is now obsolete and the closest equivalent is the WPH620PSNNN-NN controller. The new WPH600 series has upgraded features; for reference, here is the description of the old model:
proportional control outputs, 120 VAC, pre-wired wph420 with 10’ cables, with (2) e90495 connectors for ew pumps, no 4-20 mA output, none