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WB, used to determine the resistance of an unknown resistor value. In this example there is an incandescent lamp, and a mosfet.
1. Since all resistors in the bridge when balanced are the same, the upper ohmmeter will show the equivalent resistance of two resistors in series in parallel with two other resistors in series.
2. An unknown resistor is placed in the lower leg in series with the variable resistor.
3. There are 2 switches, left connects left resistor to the variable resistor, right switch connects right resistor to variable resistor. The two lower spdt switches select either to read the resistance with the Ohmmeter or with the bridge, those two switches have to be set opposite of each other, since you can not read both resistors at once because of the combined resistance.
OPERATION:
4. Flip lower left spdt down to select the left unknown resistor, and adjust the pot until the amp meter nulls out and shows zero current, the bridge is balanced, at this time the resistance reading on the lowwer side of the pot is the value of the unknown resistor as shown in this example.
5. To select the right resistor, set the right spdt up, the balancing of the bridge is the same as above.
You can verify the finding by using the ohmeter by flipping the spdt switch to the down position for the lamp, and up for the mosfet, and it should agree with the value shown on the left side of the pot.
I hope my instructions are of help, if not, I apoloigise. Remeber that you can play with the settings of the lamp and mosfet to change their resistance.
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