The Walchem WDT400-1N2U controller is now obsolete and the closest equivalent is the WCT600PSSNN-BN controller. The new WCT600 series has upgraded features; for reference, here is the description of the old model:
Dual cooling tower controller, 120 VAC, prewired, no 4-20 mA outputs, two graphite electrodes & loose flow switches, 20 ft cables, integrated datalogging and config file import/export via usb flash stick.