The instruments are designed to indicate position along the path of the plug of control and shut-off valves on which they are installed. The indication can be either in limit positions (with the help of microswitches and detectors) or continuous one (with the help of potentiometer or electrooptic device). Both functions, limit positions indication and continuous indication, can be combined. These instruments can be installed on either rotary valves or lift valves. Their housing and cap are made of anodized aluminum with epoxy coating. Circular sealing rings between the housing and the cap and on the axis make the instruments explosion-proof and protected from dust and moisture. The instruments exclude parts made of copper or copper alloys, which are in contact with the air. The absence of mechanical contact in contactless position detectors and optoelectronic sensors ensures the following:
almost absolute insensitivity to vibration and electrical noise
weak friction force during operation
almost limitless service life
easily achieved intrinsic safety
Operation Principle The prism mechanically connected with the valve plug follows its displacement by means of gear and rod system (in case of a lift valve). The beam of light from the LED fixed on the housing is reflected by the prism upon the fixed disk. The disk has three tracks. One of them is resistance track, another — conducting track, and photosensitive track is located between them. The beam of light, reflected upon the photosensitive track, creates a bridge between two other tracks and functions as potentiometer slider regulating voltage in point C for power voltage Va — Vb. Alternating voltage Va — Vс, generated like this, is electronically converted to 4—20 мА signal. This type of sensor does not have any friction and does not generate any sparks or electric noise. It is intrinsically safe, insensitive to vibration and has an extremely long service life.