The Walchem WPH420-342U controller is now obsolete and the closest equivalent is the WPH600 controller. The new WPH600 series has upgraded features; for reference, here is the description of the old model:
pH/ORP controller, proportional control outputs, 120 VAC, pre-wired WPH420 with 10’ cables, with (2) e90495 connectors for ew pumps, single isolated analog (4-20 mA) output, submersion flat ph electrode w/preamp (wel-phf-21), integrated datalogging and config file import/export via USB flash stick.