TM 1-1500-204-23-4 than  one-half  of  the  minimum  scale  division),  examine lines    and    connections    for    security    and    anchorage. When   lines   are   secure   and   anchored   properly   and pointer still oscillates, replace indicator. (b) Zero check test. At zero indication,  errors  must  not  exceed  tolerances  specified in table 4-11.  When tolerances listed in table 4-11 are exceeded, indicator shall be replaced. i. Remote Reading Pressure Indicators. Principles   of   operation,   types,   and   testing   of   remote reading     pressure     indicators     are     described     in     the following paragraphs. (1)     Principles     of     operation     and     types. Remote    reading    pressure    indicators    are    connected indirectly to the pressure source by electrical transmitters and wiring.  The transmitters are connected directly to the pressure source by tubing or hose.  As the pressure increases or decreases, the mechanism in the transmitter   is   displaced.      When   the   mechanism   is displaced,  a  signal  is  sent  to  the  indicator  through  the electrical   wiring   which   causes   the   mechanism   in   the indicator  to  turn  to  a  corresponding  position  as  that  of the transmitter, thus giving an indication of the pressure being   measured.      This   type   system   is   called   self- synchronous     (autosyn),     and     may     be     adapted     to practically  all  pressure  measuring  needs.    The  autosyn system    of    transmitting    pressure    readings    may    be incorporated   for   use   with   oil   pressure,   fuel   pressure, multi-purpose, hydraulic pressure, and manifold pressure indicators. Table 4-9.  Static Friction Error (Counter Drum Pointer) (Vibrator Inoperative) Test point altitude Tolerance (feet) (feet) 500 .......................................... 70 1,500 .......................................... 70 2,500 .......................................... 70 3,500 .......................................... 70 7,500 .......................................... 80 12,500 .......................................... 90 17,500 .......................................... 110 22,500 .......................................... 120 32,500 .......................................... 180 35,500 .......................................... 300 42,500 .......................................... 300 (2)    Testing.        The    following    paragraphs describe    tests    and    replacement    criteria    for    remote reading pressure indicators. (a) Continuity check test.  Test wiring for  proper  continuity  as  specified  in  applicable  wiring diagram. (b)    Master    transmitter    test.        Test indicators   and   transmitters   with   a   synchro   test   set. When  either  indicator  or  transmitter  is  faulty,  it  will  be replaced. (c) Zero check test.  With ac power on (26V,  400Hz),  error  at  zero  indication  must  not  exceed tolerances specified in table 4-12.  When errors exceed tolerances listed in table 4-12 and wiring and transmitter are    in    correct    working    order,    the    indicator    will    be replaced. j.   Tachometer Systems.    Principles  of  operation, types, and testing of tachometer systems are described in the following paragraphs. (1)     Principles     of     operation     and     types. Tachometer systems are independent instrument systems  which  furnish  their  own  operating  power.    A tachometer system consists of an indicator, a generator, and  connecting  wiring.    Synchronous  rotor  three-wire, synchronous    rotor    two-wire,    dual    synchronous    rotor three-wire, and dual synchronous rotor two-wire tachometer systems are the most common types. (2)    Testing.        The    following    paragraphs describe  tests  and  replacement  criteria  for  tachometer systems. Table 4-10.  Pressure Altitude Difference (Counter Drum Pointer) Pressure Altitude (inches of difference mercury (Hg)) (feet) 28.10 ................................................. -1727 28.50 ................................................. -1340 29.00 ................................................. -863 29.50 ................................................. -392 29.92 ................................................. 0 30.50 ................................................. +531 30.90 ................................................. +893 31.00 ................................................. +983 4-20