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Wheatstone Bridge Simulation

Design Bridge by selecting value for R1, R2, Rs, Vs and Rx. Next press Enter. When you click ENTER, Rx is randomly changed to a value between 30% and 130% of its original value. You are to determine value of Rx using the Wheatstone Bridge that you just designed. Go to Bridge Balance below. Make no changes to Bridge Design until you have completed Bridge Balance. Remember clicking ENTER changes Rx

Bridge Design


           

Wheat 3.gif (4178 bytes)Wheatstone bridge with DC amplifier and meter assembly in place of  Galvonometer. (Galvonometers are difficult in script.)

Bridge Balance

Rvariable

Meter Reading(in millivolts)+ or - 20 millivolts Full Scale.

Vs = Voltage Source. Could be a battery or power supply.
Rs = Internal resistance of battery or power supply.
         For ideal regulated power Rs = 0

Rx =  unknown resistor between 30% and 130% of  value you entered for Rx.
Rv = Variable precision resistor or or Decade Box.

IA = Instrumentation Amplifier. + or - 20 mv produce max output.

Meter Reading: Meter that reads + or - Full Scale when input = + or - 20 mv. Note that in reality FS output of the IA could be + or - 10 volts and the user could use a digital voltmeter and read each volt as 2 mv.

Practicle limitations for Rv :  If you are trying to simulate balancing a bridge using a precision decade box with a least significant digit of .1 ohms you should only ENTER a number with one decimal place for Rv. Likewise their are practicle upper and lower limitions for slidewire variable resistances.

Though this is not a troubleshooting exercise, it is a practicle excercise in the use of bridges. Impedance bridges are more prevalent in electronics laboratories than pure resistance bridges are.

Why did'nt you use a multimeter to measure the output of the Instrumentation Amplifier?
Remember that the output of Instrumentation will still be clipped at above 20 mv input. I could reduce the gain of the amplifier but that would reduce resolution. If I were not concerned with extreme resolution, I would not use a bridge to measure a resistor.