File:Moving coil instrument principle.png

 /*
 =======================================================
 Demonstrating the principle of a moving coil instrument
 -------------------------------------------------------
 Created by Søren Peo Pedersen - see my user page at
 http://da.wikipedia.org/wiki/Bruger:Peo
 =======================================================
 */
 
 #declare CloseUp=yes;
 #declare Fontname="arialbd.ttf";
 
 
 global_settings {max_trace_level 256}
 
 #local txtMetal=texture {
   pigment {color rgb .5}
   finish {
       metallic
       phong 1
       reflection .5
       }
   }
 
 #include "functions.inc"
 #local CoilSpring=isosurface {function {f_spiral(-x,z/5,y,.2,.01,1.34,0,0,0)}
     contained_by { box {<-2,-2,-.2>,<2,2,.2>} }  // container shape
     accuracy 0.001                      // accuracy of calculation [0.001]
     max_gradient 4                      // maximum gradient the function can have [1.1]
     texture {txtMetal}
     }
 
 #macro txtCoilYoke(Transparency)
     texture {pigment {color rgbt <.5,1,0,Transparency>} finish {ambient .4}}
 #end
 
 #macro MovingPart(Transparency)
   #local txtCopper=texture {  // Texture for copper wire in coil
     pigment {color 
       #if (Transparency=0)
         rgb <.5,.25,.15>
       #else
         rgbt <1,.5,.3,Transparency>
       #end
       }
     finish {            
       #if (Transparency=0)
         metallic 1
         reflection rgb <1,.5,.3> 
         phong 1
         ambient .4
       #end
       }
     }
   
   #local FramePart=merge {  // One of four "sides" in the square-shaped coil
     difference {  // Staright parts of coil yoke
       box {<-.3,1,-1.00001>,<.3,1.5,1.00001>}
       box {<-.25,1.05,-2>,<.25,2,2>}
       txtCoilYoke(Transparency)
       }
     difference {  // Rounded corners of coil yoke
       cylinder {<-.3,1,-1>,<.3,1,-1>,.5}
       box {<-.25,0,-2>,<.25,2,0>}
       box {<-1,1,-2>,<1,2,-1> inverse}
       txtCoilYoke(Transparency)
       }
     
     #local n=0; // Outermost layer of windings on coil
     #while (n<11)
         cylinder {<-.275+.05*n,1.4,-1.00001>,<-.275+.05*n,1.4,1.00001>,.025 texture {txtCopper}}
         intersection {
             torus {.4,.025}
             box {<0,-1,-1>,<1,1,0>}
             rotate <0,0,90>
             translate <-.275+.05*n,1,-1>
             texture {txtCopper}
             }
         #local n=n+1;
     #end
     
     #local n=0;
     #while (n<7)
       cylinder {<.225,1.35-.05*n,-1.00001>,<.225,1.35-.05*n,1.00001>,.025 texture {txtCopper}}
       intersection {
         torus {.35-.05*n,.025}
         box {<0,-1,-1>,<1,1,0>}
         rotate <0,0,90>
         translate <.225,1,-1>
         texture {txtCopper}
         }
       #local n=n+1;
     #end
     
     }
   
   #merge {  // The entire mobile coil on its yoke:
       #object {FramePart}
       #object {FramePart rotate <90,0,0>}
       #object {FramePart rotate <180,0,0>}
       #object {FramePart rotate <270,0,0>}        
       box {<-.03,0,-1.79>,<.03,5,-1.81> // Needle
         pigment {color rgbt <0,0,0,Transparency>}
   // Changed by user:xorx due to this comment
         rotate <0,0,-90>
         }
       }
 #end
 
 #declare MagnetPoleShoe=merge {
   cylinder {<-1.44222,-.9,-.8>,<-1.44222,-.9,.8>,.1}
   cylinder {<-1.44222, .9,-.8>,<-1.44222, .9,.8>,.1}
   sphere {<-1.44222,-.9,-.8>,.1}
   sphere {<-1.44222, .9,-.8>,.1}
   sphere {<-1.44222,-.9, .8>,.1}
   sphere {<-1.44222, .9, .8>,.1}
   cylinder {<-1.44222,-.9,-.8>,<-1.8,-.9,-.8>,.1}
   cylinder {<-1.44222,-.9, .8>,<-1.8,-.9, .8>,.1}
   cylinder {<-1.44222, .9,-.8>,<-1.8, .9,-.8>,.1}
   cylinder {<-1.44222, .9, .8>,<-1.8, .9, .8>,.1}
   box {<-1.8,.9,-.8>,<-1.44222,1,.8>}
   box {<-1.8,-1,-.8>,<-1.44222,-.9,.8>}
   difference {
     box {<-1.8,-.9,-.9>,<0,.9,.9>}
     cylinder {<0,0,-5>,<0,0,5>,1.7}
     }
   difference {
     box {<-1.799999,-.837596,-.8>,<0,.837596,.8>}
     cylinder {<0,0,-5>,<0,0,5>,1.6}
     }
   difference {
     merge {
       torus {1.7,.1 rotate <90,0,0> translate <0,0,-.8>}
       torus {1.7,.1 rotate <90,0,0> translate <0,0,.8>}
       }
     plane {<0,1,0>,0 rotate <0,0,31.9657>}
     plane {<0,-1,0>,0 rotate <0,0,-31.9657>}
     }
   texture {txtMetal}
   }
 
 #object {MagnetPoleShoe}
 #object {MagnetPoleShoe scale <-1,1,1>}
 
 #if (CloseUp)
   // Changed by user:xorx due to this comment
   #object{MovingPart(0) translate <0,0,-.000001> rotate <0,0,135>}
   #object {MovingPart(.7) rotate <0,0,45>}
 #else
   #object{MovingPart(0) rotate <0,0,100>}
 #end
 
 cylinder {<0,0,-2>,<0,0,-1.5>,.4 txtCoilYoke(0)}
 cylinder {<0,0,1.5>,<0,0,1.7>,.4 txtCoilYoke(0)}
 cylinder {<0,0,-2.5>,<0,0,-2>,.1 texture {txtMetal}}
 cylinder {<0,0,1.7>,<0,0,2.2>,.1 texture {txtMetal}}
 
 #object {CoilSpring translate <0,0,1.6>}
 #object {CoilSpring translate <0,0,-1.6>}
 
 merge { // Core inside moving coil
     cylinder {<0,0,-.9>,<0,0,.9>,.8}
     cylinder {<0,0,-.8>,<0,0,.8>,.9}
     torus {.8,.1 rotate <90,0,0> translate <0,0,-.8>}
     torus {.8,.1 rotate <90,0,0> translate <0,0,.8>}
     texture {txtMetal}
     }
 
 merge { // Frame & screw for mechanical adjustment
   difference {
     box {<-.2,-2,-2.8>,<.2,.2,2.5>}
     box {<-1,-1.25,-2.2>,<1,1,1.9>}
     box {<-1,-1.6,-1.5>,<1,1,1.5>}
     }
   cylinder {<0,0,-2.8>,<0,0,-3.3>,.2}
   difference {
     cylinder {<0,0,-3.3>,<0,0,-4>,.4}
     sphere {<0,0,-2>,1.6 inverse}
     box {<-1,-.1,-5>,<1,.1,-3.4>}
     }
   pigment {color rgb <0,.5,1>}
   finish {ambient .4}
   }
   
 difference {  // Horse-shoe permanent magnet
   merge {
     box {<-3.8,-1,-1>,<3.8,3,1>}
     cylinder {<0,3,-1.000001>,<0,3,1.000001>,3.8}
     }
   box {<-1.8,-2,-2>,<1.8,3,2>}
   cylinder {<0,3,-2>,<0,3,2>,1.8}
   pigment {
     object {
       union {
         text {ttf Fontname,"S",1,0 scale 3.1 translate <-3.7,-.85,-1.5>}
         difference {
           plane {<-1,0,0>,0}
           text {ttf Fontname,"N",1,0 scale 3.1 translate <1.9,-.85,-1.5>}
           }        
         }
       color rgb 1
       color rgb <1,0,0>
       }
     }
   finish {ambient .4}
   }   
 
 box {<-4.3,3,-1.7>,<4.3,6,-1.68>  // Scale behind needle:
   pigment {
     object {
       union {
         #local n=0;
         #while (n<101)
           #local h=5.1;
           #if (n/5=int(n/5)) #local h=5.2; #end
           #if (n/10=int(n/10))
             #local h=5.3;
             #local Number=text {ttf Fontname,str(n/10,0,0),.04,0 scale .5}
             #object {
               Number
               translate <(min_extent(Number).x-max_extent(Number).x)/2,5.35,-1.71>
               rotate <0,0,45-.9*n>
               }
           #end
           box {
             <-.01,4.8,-1.71>,<.01,h,-1.69>
             rotate <0,0,45-.9*n>
             }
           #local n=n+1;
         #end
         }
       color rgbt <1,1,1,.5>
       color rgbt <0,0,0,.5>
       }
     }
   finish {ambient .4}
   }
 
 difference {
   cylinder {<0,0,-1.7002>,<0,0,-1.7001>,4.75}
   cylinder {<0,0,-2>,<0,0,-1>,4.55}
   box {<0,0,-2>,<9,9,-1> inverse rotate <0,0,45>}
   pigment {color rgb 0}
   finish {reflection .95}
   }
 
 #declare Spotty=pigment {
   bozo
   color_map {
     [0 color rgb .5]
     [1 color rgb 1]
     }
   scale .05
   }
   
 sky_sphere {
   pigment {
     gradient z
     pigment_map {
       [0 Spotty]
       [.8 Spotty]
       [.913 color rgb <1,1,1>]
       [1 color rgb <1,1,1>]
       }
     scale 2
     translate <0,0,-1>
     rotate <15.5,28.5,0>
     }
   }
 
 camera {
   up <0,1,0> right <.93,0,0>
   location <-5,5,-9>
   #if (CloseUp)
     look_at <0,-.45,-.8> angle 24
   #else
     look_at <-.55,2.4,-.8>
   #end
   }
 
 light_source {<50,150,100> color rgb 1}
 light_source {<-100,80,-150> color rgb 1}