The Walchem WDEC410-5NBNN 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 hardwired, cable glands, no 4-20 mA output, in-line PEEK sensor w/stainless steel adapter (0.1 - 1.0 ms/cm, 20 ft cable), no second sensor