﻿136 
  Dr. 
  Drysdale 
  on 
  the 
  Use 
  of 
  Shunts 
  and 
  Transformers 
  

  

  by 
  Mr. 
  Murdoch* 
  this 
  permeameter 
  was 
  criticized 
  as 
  

   employing 
  a 
  very 
  small 
  specimen 
  ; 
  but 
  this 
  is 
  precisely 
  

   what 
  has 
  been 
  aimed 
  at 
  in 
  its 
  design. 
  It 
  appears 
  to 
  be 
  of 
  

   great 
  importance 
  that 
  permeameters 
  for 
  castings 
  or 
  forgings 
  

   should 
  be 
  capable 
  o£ 
  being 
  employed 
  on 
  the 
  bulk 
  of 
  the 
  

   metal 
  itself, 
  without 
  extra 
  machined 
  specimens, 
  and 
  up 
  

   to 
  the 
  present 
  no 
  other 
  instrument 
  has 
  been 
  devised 
  which 
  

   meets 
  this 
  requirement. 
  

  

  The 
  writer's 
  hearty 
  thanks 
  are 
  due 
  to 
  Mr. 
  A. 
  C. 
  Jolley 
  for 
  

   the 
  considerable 
  amount 
  of 
  work 
  involved 
  in 
  carrying 
  out 
  

   the 
  tests. 
  Mr. 
  C. 
  M. 
  Dowse 
  has 
  also 
  rendered 
  considerable 
  

   assistance 
  in 
  the 
  later 
  tests. 
  

  

  IX. 
  The 
  Use 
  of 
  Shunts 
  and 
  Transformers 
  with 
  Alternate 
  

   Current 
  Measuring 
  Instruments. 
  By 
  Charles 
  V. 
  

   Drysdale, 
  JD.Sct 
  

  

  [Plate 
  IV.] 
  

  

  THE 
  growing 
  demand 
  for 
  instruments 
  for 
  alternate-current 
  

   measurement, 
  of 
  considerable 
  range 
  and 
  accuracy, 
  lias 
  

   called 
  attention 
  to 
  some 
  of 
  the 
  difficulties 
  attending 
  their 
  

   production, 
  especially 
  to 
  their 
  limited 
  range. 
  As 
  alternate- 
  

   current 
  instruments 
  measure 
  the 
  root-mean-square 
  values 
  of 
  

   the 
  P.D. 
  or 
  current, 
  it 
  necessarily 
  follows 
  that 
  the 
  deflecting 
  

   torque 
  falls 
  very 
  rapidly 
  as 
  the 
  P.D. 
  or 
  current 
  is 
  decreased, 
  

   For 
  most 
  commercial 
  instruments, 
  it 
  may 
  be 
  taken 
  that 
  a 
  ten- 
  

   fold 
  range 
  of 
  torque 
  is 
  the 
  utmost 
  possible 
  for 
  accurate 
  

   reading, 
  so 
  that 
  when 
  the 
  deflexion 
  is 
  proportional 
  to 
  the 
  

   torque 
  the 
  range 
  of 
  an 
  A.C. 
  instrument 
  can 
  only 
  be 
  of 
  the 
  

   order 
  of 
  3 
  to 
  1 
  except 
  by 
  the 
  employment 
  of 
  double 
  coils 
  or 
  

   auxiliary 
  devices. 
  The 
  auxiliary 
  devices 
  which 
  may 
  be 
  

   employed 
  are 
  transformers 
  for 
  electromagnetic 
  ammeters, 
  

   voltmeters, 
  and 
  wattmeters 
  ; 
  shunts 
  for 
  ammeters 
  and 
  watt- 
  

   meters, 
  series 
  resistances 
  for 
  electromagnetic 
  voltmeters, 
  and 
  

   condensers 
  and 
  split 
  resistances 
  for 
  electromagnetic 
  voltmeters. 
  

   Of 
  these, 
  the 
  use 
  of 
  shunts 
  and 
  transformers 
  may 
  give 
  rise 
  to 
  

   serious 
  errors, 
  and 
  it 
  is 
  proposed 
  here 
  to 
  investigate 
  the 
  

   amount 
  of 
  these 
  errors 
  and 
  the 
  conditions 
  for 
  their 
  elimi- 
  

   nation. 
  

  

  In 
  dealing 
  with 
  any 
  shunting 
  or 
  transforming 
  device 
  1 
  we 
  

   must 
  bear 
  in 
  mind 
  that 
  it 
  may 
  cause 
  errors 
  in 
  two 
  ways: 
  — 
  (a) 
  by 
  

   the 
  multiplying 
  power 
  of 
  the 
  shunt 
  or 
  the 
  ratio 
  oi 
  the 
  trans- 
  

   former 
  being 
  affected 
  by 
  frequency, 
  &c; 
  and 
  (6) 
  by 
  a 
  phase 
  

   displacement 
  being 
  introduced 
  between 
  the 
  current 
  or 
  P.D. 
  

  

  * 
  Electrician, 
  vol. 
  lx. 
  ]>. 
  245. 
  

  

  t 
  Communicated 
  by 
  the 
  Physical 
  Society 
  ■. 
  road 
  March 
  27, 
  L90S. 
  

  

  