The Walchem WDEC410-5NJNN 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 (10.0 - 100 ms/cm, 20 ft cable), no second sensor