Patent attributes
A valve positioner monitors a valve stem position by remotely sensing a magnet attached to a coupler shaft that does not penetrate a sealed enclosure surrounding the positioner. A torsion spring, which can be helical or spiral, concentrically surrounds the shaft and is fixed to the shaft and frictionally coupled to a fixed surface by a clutch ring that coaxially surrounds the spring and is vertically pressed against the fixed surface. The torsion spring thereby suppresses backlash, vibration, and chatter by maintaining a torsional force on the shaft. The clutch ring can include a notch or slot cooperative with a key tab rotationally fixed to the coupler shaft so as to limit a range of rotation of the coupler shaft. The positioner is rendered compact by the concentric arrangement of its elements, so that embodiments can be used in place of legacy positioners.
