LINEAR VIBRATION TESTING AND ADJUSTING V Peak  =  52.36 D x F x 10^-6 Where V Peak  =      Vibration   velocity   in   inches per second peak. D =  Peak-to-peak displacement in mils (1 mil = 0.001 in). F =        Frequency    in    cycles    per minute (cpm). Acceleration  measurements  or  "gs"  are  commonly  used where  relatively  large  forces  are  applied.    At  very  high frequencies (60,000 cpm) it is perhaps the best indicator of vibration. The vibration acceleration can be calculated as: g Peak = 1.42 D x F2 x 10^-8 Measurement The  exact  nature  of  linear  vibration  is  difficult  to  define without   instrumentation.      The   human   senses   are   not adequate to detect relationships between the magnitude of    displacement    of    a    vibration    and    its    period    of occurrence.        For    instance,    a    first    order    (1    x    rpm) vibration  of  0.010  in  (0.254  mm)  displacement  may  feel about  the  same  as  a  third  order  measurement  of  0.001 in  (0.026  mm).    However,  the  severity  of  vibration  does correlate  reasonably  well  with  levels  of  perception  and annoyance. Establishing  the  vibration  frequency  is  necessary  when analyzing this type of problem.  It allows identification of the engine component or mass  system which is causing the  vibration.    In  discussions  of  vibration,  the  frequency of the motion is commonly referred to in terms of "order" of  vibration.    In  an  engine,  the  order  of  vibration  is  the number   of   vibratory   cycles   exhibited   by   a   component during one revolution of the crankshaft. Order = Vibration Frequency (cpm) Engine Speed (rpm) Overall  vibration  motion  is  the  vector  sum  of  the  motion of all the orders.  In other words, individual order motions will    add    or    subtract    to    produce    the    overall.        This measurement    is    not    used    to    identify    problems    or establish  limits,  but  rather  as  an  indication  of  the  total linear vibration motion. A vibration analyzer is a prerequisite to troubleshooting a problem of this nature.  A unit that measures frequencies and   amplitude   is   suggested.      Further,   the   analyzer should  be  rugged  and  easily  understood.    Good  results have  been  obtained  with  the  IRD  Mechanalysis  Model 320.  It is offered by: IRD Mechanalysis, Inc. 6150 Huntley Road Columbus, Ohio 43229 All   measurements   must   be   made   on   the   main   rigid structural  members  of  the  engine  and  generator.    The instrument pickup must be  positioned  on  the  crankshaft centerline  at  the  locations  shown  on  the  sample  form. Measurements     (except     torque     reaction     and     some misalignment)   can   be   made   at   no-load   operation.      If measurements  are  taken  while  the  generator  is  loaded, the   magnetic   field   of   the   generator   leads   must   be avoided. If    excessive    linear    vibration    motion    is    present    or suspected,  an  initial  measurement  should  be  made  to identify   the   source   prior   to   starting   corrective   action. These   measurements   are   to   be   checked   against   the applicable  limits  shown  in  the  graph  on  Page  107.    A sample    form    is    described    in    this    data    sheet    for convenient   recording   of   raw   data   at   various   engine speeds  (generator  frequencies).    This  form  can  be  used for the basic engine, single-bearing generators, and two- bearing generators. Identification Experience    has    shown    that    in    order    of    decreasing importance,    the    primary    sources    of    linear    vibration motion problems are: 1.  Misalignment of engine and driven equipment. 2.  Unbalance of rotating parts. 3.        Resonance    from    structural    mass    (weight)    and stiffness (rigidity) combinations. 4.  Torque reaction. 5.  Cylinder misfiring. 6.  Combustion forces. 7.  Unbalance of reciprocating parts. As  test  data  is  reviewed,  if  excessive  vibration  motion exists, it will be due to one of the following causes: 104