The ST977 is a rugged, sealed replacement sensor designed for the SA877 and SA878 insertion / retraction assemblies. The patented solid state reference cell features the unique IonTrap™ design for extended service life in the most severe applications. The body, with integral bulb guard and anti-blowout restraint, is moulded from chemically resistant Ryton (PPS) and the reference junction is porous Teflon. Built-in temperature compensators are available. Sensor also available in ORP (Redox) version.