The Walchem WDEC410-1NMNN controller is now obsolete and the closest equivalent is the WCN600 controller. The new WCN600 series has upgraded features; for reference, here is the description of the old model:
Dual input 120 VAC, prewired, no 4-20 mA output, submersion PEEK sensor (100 - 1000 ms/cm, 20 ft cable), no second sensor