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» PONTAVI «
WHEATSTONE BRIDGE
( A Precision Measurement Device for Resistances )


Dimensions  ( W x D x H )  11 cm x 20 cm x 6.5 cm  /   4_1/4" x 8" x 2_1/2"

WHEATSTONE BRIDGE (= Resistance Measurement )   H&B   1622520   » PONTAVI «
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HARTMANN & BRAUN AG, Frankfurt am Main / Germany                     (1960)


T H E O R Y :   WHY looks the Scale of the Wheatston Bridge "LOGARITHMIC" ?
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See the wire diagram in the book under the bridge: The contact divides the
resistance wire in a left ( R-Left= RL ) and a right side ( R-Right= RR ).  
The instrument shows "ZERO", when the fraction ...

     ( RL / RR )  =  ( RN / RX )     ==>>    RX  =  RN * ( RR / RL )

Where RN is the known resistance ( set with the SELECT switch ) and RX is
the unknown resistance, the TEST object.

Let the resistance wire be 2 UNITS.  Then the contact "sees" ...

RL    0.6  0.7  0.8  0.9  1.0  1,1  1.2  1.3  1.4  1.5  1.6  1.7  1.8  1.9
   =  -+----+----+----+----+----+----+----+----+----+----+----+----+----+-
RR    1.4  1.3  1.2  1.1  1.0  0.9  0.8  0.7  0.6  0.5  0.4  0.3  0.2  0.1

         0.5               1                2       3    4  5  6 7891015
SCALE ----+----------------+----------------+-------+----+--+--+-++++-+---

The scale shows the fractions of RL/RR =

 0.5=0.666/1.333          1/1        2=1.333/0.666
                                               3=1.5/0.5
                                                    4=1.6/0.4
                                                     5=1.666/0.333
                                                       6=1.7145/0.2855
                                                           7=1.75/0.25
                                                           8=1.779/0.221
                                                              9=1.8/0.2
                                                            10=1.819/0.181
                                                             15=1.875/0.125
R E M A R K :
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H&B  gave its  Multi(V/A)-Meters  the brand name  »MULTAVI«.  Here the name
»PONTAVI«  was chosen from  "PONT" = French = "Bridge".   The instrument is
powered by a 4.5 V Battery ( 6 cm x 6.5 cm x 2 cm / 2_3/8" x 2_1/2 x 3/4" )

H I S T O R I C   R E M A R K      from   » WEBSTER'S POCKET ENCYCLOPEDIA «
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Invented by the British physicist Sir Charles Wheatstone (1802-1875). It is
of historical interest, that  ( together with W.F.Cooke )  he invented also
an electric telegraph  at about the same time as US inventor  Samuel Morse.

                  Have a Look at the L-C Bridge »INKAVI« ...
                  Have a Look at a transistorized R-L-C Bridge ...
impressum:
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© C.HAMANN        http://public.beuth-hochschule.de/~hamann        11/14/09