Tokyo Sokki Kenkyujo TC-32K Operation Manual Download

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10.1 Wire connection of strain gauge

10-2

Automatic  compensation  of  lead  wire  is  not  available  even  if  you  perform
measurement  with  Comet  B.    Similar  to  Comet  A,  the  measurement  value  must
be  compensated  separately.    For  more  detail,  refer  to

“10.3 Complete

Compensation Method of Strain

”.

10.1 Wire connection of strain gauge

This section explains connection methods of strain gauges available by TC-32K. The next section
shows decreasing rate of sensitivity due to extension of strain gauge.

■ 1-gauge 4-wire method

This  method  uses a  4-core  lead  wire  for  connection  of  a  strain  gauge.    It  eliminates  gauge  factor
drop  due  to  lead  wire  resistance  and  measurement  error  caused  by  contact  resistance.    It  also
allows elimination of initial unbalance caused by  the lead wire including thermal output caused by
the temperature change of the lead wire.
For quarter bridge 3-wire method, use of a lead wire as thick and short as possible is recommended
for  minimizing  errors  caused  by  the  lead  wire  resistance.    However,  with  the  1  gauge  4-wire
method, thin lead wires and/or connectors can be used for connection  and extension.    As a result,
it  allows  more  efficient  wiring  works,  prevents  wiring  errors,  and  reduces  costs  for  strain
measurement by re-use of lead wires.

■ Quarter bridge 2-wire method

Internal fixed resistors of the instrument are used for configuring a bridge circuit except the active
gauge (strain gauge which detects strain).

Resistance of the lead wire connecting the strain gauge enters serially only in the active gauge arm

of  the  bridge  circuit.    If  a  thin  and/or  long  lead  wire  is  used,  initial  unbalance  may  become  too
large to be balanced, and thermal output caused by the temperature change of the lead wire is mixed
with  strain  reading.    Also,  temperature  compensation  for  the  strain  gauge  is  not  possible.     For
more accurate measurement, the use of quarter bridge 3-wire method is recommended.
This  quarter  bridge  2-wire  method  can  be  measured  in  sensor  mode  of  quarter  bridge  3-wire
(1G3W) by connecting B and C of the terminal block.    However, the TC-32K does not support this
way formally.

■ Quarter bridge 3-wire method

A 3-core lead wire is used for connection to compensate the influence of lead wire in quarter bridge
2-wire  method.    Since  the  resistance  of  the  lead  wire  enters  also  in  the  fixed  resist or  arm  of  the
bridge  circuit  as  well  as  in  the  active  gauge  arm,  affection  of  initial  unbalance  caused  by  the  lead
wire  resistance  is  eliminated  and  temperature  compensation  for  the  lead  wire  is  also  possible.
However, temperature compensation for the strain gauge is not possible.

■ Half bridge method

Internal fixed resistors are used for two arms of bridge circuit. Strain gauges of the same lot
should be used, and a 3-core wire is used for connection. Temperature compensation for the strain
gauge and for the lead wire is possible at the same time, and affection of initial unbalance caused by
the lead wire is eliminated.

■ Full bridge method

Strain  gauges  configure  all  4  arms  of  bridge  circuit  without  using  internal  fixed  resistors.    This
method is used for transducers, and also for measurement of torque or bending where large output is
preferred,  but  not  often  used  for  general  stress  measurement  works.    When  the  bridge  circuit  is
configured  in  the  area  where  the  strain  gauges  are  mounted,  initial  unbalance  and  affection  of
temperature can be eliminated even when the lead wire is extended.

Note