The Walchem WEDT410-521U controller is now obsolete and the closest equivalent is the WCT600 controller. The new WCT600 series has upgraded features; for reference, here is the description of the old model:
Cooling tower controller -bleed & feed w/2 biocides, hardwired, cable glands, two isolated analog (4-20 mA) outputs, electrodeless conductivity & ph sensors and tees, 20 ft cable (for inline mounting), data logging and configuration file capability.