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

 ``` WHEATSTONE BRIDGE (= Resistance Measurement ) H&B 1622520 » PONTAVI « *************************************************************************** HARTMANN & BRAUN AG, Frankfurt am Main / Germany (1960) T H E O R Y : WHY looks the Scale of the Wheatston Bridge "LOGARITHMIC" ? =========================================================================== 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 : =========================================================================== H&B gave its Multi(V/A)Meters the brand name »MULTAVI«. Here the name »PONTAVI« was chosen from "PONT" =French= "Bridge" H I S T O R I C R E M A R K from » WEBSTER'S POCKET ENCYCLOPEDIA « =========================================================================== 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 a transistorized R-L-C Bridge ... impressum: *************************************************************************** © C.HAMANN http://public.beuth-hochschule.de/~hamann 11/10/09 ```