Slide valve position indicator

Abstract

The angular displacement of an inclined cam about the compressor slide valve shaft rotates an annular surface having a helically inclined face aligned with and spaced apart from a sensor head of a magnetic sensor mounted to the compressor. The rotation provides a linear variation in the size of the gap between the sensor head and the inclined ramp which directly corresponds to the compressor slide valve position between its fully closed and fully open positions. Linear variation in the size of the gap produces a correspondingly linear output signal from the magnetic sensor which provides the input for an analog input card in an associated programmable logic controller to determine the slide value position.

1 . A slide valve position indicator comprising:
 a magnetic sensor having a magnetic sensor head at a first end thereof and adapted to output an electrical signal to a processor,   a rigid mount for rigidly mounting said magnetic sensor in spaced apart relation to a slide valve position indicating shaft of a screw compressor,   a ferrous metal cam mountable to the shaft, and an inclined cam surface formed on said cam in opposed facing spaced relation to said sensor head spaced apart by a sensor range spacing,   said inclined cam surface formed so as to reduce said sensor range spacing at a first end of said cam surface and to increase said sensor range spacing at a second end of said cam surface and so as to linearly vary said sensor range spacing therebetween as said shaft moves said cam relative to said sensor head in linear correspondence with a corresponding slide valve position.   
   
   
       2 . The indicator of  claim 1  wherein said inclined cam surface is a smoothly helical surface. 
   
   
       3 . The indicator of  claim 2  wherein said cam is formed on a disc mountable to a distal end of the shaft so that said disc is orthogonal to the shaft. 
   
   
       4 . The indicator of  claim 3  wherein said cam surface is formed around an annular perimeter of said disc and said helical surface varies by said sensor range spacing relative to said sensor head. 
   
   
       5 . The indicator of  claim 4  wherein said sensor range spacing varies over a range corresponding substantially to a detection range of said sensor. 
   
   
       6 . The indicator of  claim 5  wherein said mount is a rigid bracket mountable to the compressor adjacent the shaft. 
   
   
       7 . The indicator of  claim 6  wherein the sensor is elongate and held by said mount so as to be substantially parallel to said shaft and substantially orthogonal to said disc. 
   
   
       8 . The indicator of  claim 7  wherein said helical surface extends substantially 270 degrees around said shaft. 
   
   
       9 . The indicator of  claim 8  wherein said sensor range spacing is substantially in the range of 1-5 mm. 
   
   
       10 . The indicator of  claim 9  wherein said disc is steel. 
   
   
       11 . The indicator of  claim 10  wherein said electrical output of said sensor is an analog electrical current signal.