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T–53 Fig. 25    Angular Misalignment PULL AND BEARING LOADS for further instructions on summing vectors. Idler Force:  Belt installation tension can also be applied by exerting a force against an idler pulley  within  the  system  that  is  used  to  take  up  belt  slack  (see  Figure  23).    This  force  can  be applied manually, or with a spring.  Either way, the idler should be locked down after the appropriate tension has been applied. Calculating the required force will involve a vector analysis as described previously in the shaft separation section. Sonic Tension Meter:  The Sonic Tension   Meter   (Figure   24)   is   an electronic  device  that  measures  the natural  frequency  of  a  free  stationary belt  span  and  instantly  computes  the static  belt  tension  based  upon  the  belt span  length,  belt  width,  and  belt  type. This  provides  accurate  and  repeatable tension  measurements  while  using  a nonintrusive procedure (the measurement  process  itself  doesn't change  the  belt  span  tension).    A measurement   is   made   simply   by plucking  the  belt  while  holding  the sensor close to the vibrating belt span. The  unit  is  about  the  size  of  a  portable  phone  (8-1/8"  long  x  3-3/4"  wide  x  1-3/8"  thick  or 206mm  long  x  95mm  wide  x  35mm  thick)  so  it  can  be  easily  handled.    The  sensor  is  about  1/2" (13mm) in diameter for use in cramped spaces, and the unit is either battery operated for portability or  AC  operated  for  production  use.    The  unit  measures  virtually  all  types  of  light  power  and precision  belts.    A  gain  adjustment  allows  measurements  to  be  made  in  environments  with  high noise levels.  Data can also be collected through an IBM Compatible RS-232 serial port, if desired. For additional details, see the product section of this handbook. SECTION 11    DRIVE ALIGNMENT 11.1   Angular And Parallel Drive  misalignment  is  one  of  the  most  common  sources  of  drive  performance  problems. Misaligned drives can exhibit symptoms such as high belt tracking forces, uneven belt tooth wear, high noise levels, and tensile cord failure.  The two primary types of drive misalignment are angular and parallel.  Discussion about each of these types are as follows: Angular:    Angular  misalignment results  when  the  drive  shafts  are  not parallel  (see  Figure  25).    As  a  result, the  belt  tensile  cords  are  not  loaded evenly,  resulting  in  uneven  tooth/land pressure and wear.  The edge cords on the   high   tension   side   are   often overloaded  which  may  cause  an  edge cord failure that propagates across the entire belt width.  Angular misalignment often results in high belt-tracking forces as well which cause accelerated belt Fig. 23    ldler Forces Fig. 24    Sonic Tension Meter Backside Idler Inside Idler Force Force