A Wheatstone span is a device which is used to happen the unknown resisitance.
Get Full Essay Get access to this section to get all help you need with your A wheatstone bridge essay and educational issues. Get Access A Wheatstone Bridge Essay Sample A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component.
Its operation is similar to the original potentiometer. If the ratio of the two resistances in the known leg is equal to the ratio of the two in the unknown legthen the voltage between the two midpoints B and D will be zero and no current will flow through the galvanometer.
If the bridge is unbalanced, the direction of the current indicates whether is too high or too low. Detecting zero current with a galvanometer can be done to extremely high accuracy.
Therefore, ifand are known to high precision, then can be measured to high precision. Very small changes in disrupt the balance and are readily detected.
This setup is frequently used in strain gauge and resistance thermometer measurements, as it is usually faster to read a voltage level off a meter than to adjust a resistance to zero the A wheatstone bridge essay. The bridge is balanced andso the second set of equations can be rewritten as: Then, the equations are divided and rearranged, giving: From the first rule, and.
The desired value of is now known to be given as: If all four resistor values and the supply voltage are known, and the resistance of the galvanometer is high enough that is negligible, the voltage across the bridge can be found by working out the voltage from each potential divider and subtracting one from the other.
The equation for this is: No text on electrical metering could be called complete without a section on bridge circuits. The standard bridge circuit, often called a Wheatstone bridge, looks something like this: To measure resistance with a Wheatstone bridge, an unknown resistance is connected in the place of Ra or Rb, while the other three resistors are precision devices of known value.
Either of the other three resistors can be replaced or adjusted until the bridge is balanced, and when balance has been reached the unknown resistor value can be determined from the ratios of the known resistances.
A requirement for this to be a measurement system is to have a set of variable resistors available whose resistances are precisely known, to serve as reference standards.
For example, if we connect a bridge circuit to measure an unknown resistance Rx, we will have to know the exact values of the other three resistors at balance to determine the value of Rx: Each of the four resistances in a bridge circuit are referred to as arms. The resistor in series with the unknown resistance Rx this would be Ra in the above schematic is commonly called the rheostat of the bridge, while the other two resistors are called the ratio arms of the bridge.
This resistance standard shown here is variable in discrete steps: Wheatstone bridges are considered a superior means of resistance measurement to the series battery-movement-resistor meter circuit discussed in the last section. Unlike that circuit, with all its nonlinearities nonlinear scale and associated inaccuracies, the bridge circuit is linear the mathematics describing its operation are based on simple ratios and proportions and quite accurate.
It is the preferred method of resistance measurement in calibration laboratories due to its high accuracy. There are many variations of the basic Wheatstone bridge circuit. Most DC bridges are used to measure resistance, while bridges powered by alternating current AC may be used to measure different electrical quantities like inductance, capacitance, and frequency.
Its schematic diagram is as such: The low-value resistors are represented by thick-line symbols, and the wires connecting them to the voltage source carrying high current are likewise drawn thickly in the schematic.
This oddly-configured bridge is perhaps best understood by beginning with a standard Wheatstone bridge set up for measuring low resistance, and evolving it step-by-step into its final form in an effort to overcome certain problems encountered in the standard Wheatstone configuration.
If we were to use a standard Wheatstone bridge to measure low resistance, it would look something like this: We have a problem, in that the connections and connecting wires between Ra and Rx possess resistance as well, and this stray resistance may be substantial compared to the low resistances of Ra and Rx.
However, the two remaining Ewire voltage drops will cause problems, as the wire connecting the lower end of Ra with the top end of Rx is now shunting across those two voltage drops, and will conduct substantial current, introducing stray voltage drops along its own length as well.
We can manage the stray voltage drops between Ra and Rx by sizing the two new resistors so that their ratio from upper to lower is the same ratio as the two ratio arms on the other side of the null detector.
This is why these resistors were labeled Rm and Rn in the original Kelvin Double bridge schematic: The actual balance equation of the Kelvin Double bridge is as follows Rwire is the resistance of the thick, connecting wire between the low-resistance standard Ra and the test resistance Rx: However, the lower the resistances of Rm and Rn, the more sensitive the null detector will be, because there is less resistance in series with it.
Increased detector sensitivity is good, because it allows smaller imbalances to be detected, and thus a finer degree of bridge balance to be attained.
Unfortunately, though, the lower the values of Rm and Rn, the more current they will carry, which will increase the effect of any junction resistances present where Rmand Rn connect to the ends of Ra and Rx.Bridge Instruments Bridge Instruments Various types of bridge circuits are used in instrumentation.
They can operate in either deflection mode or null principle. They can operate in either deflection mode or null principle. Electronics Tutorial about the Wheatstone Bridge Circuit and how a Wheatstone Bridge can be used with transducers to produce a Wheatstone Bridge Circuit.
The Wheatstone Bridge was originally developed by Charles Wheatstone to measure unknown resistance values and as a means of calibrating measuring instruments, White Papers . Free Essay: PHY II ESSAY REPORT Wheatstone Bridge and Resistance The 19th century was as very good era of discovery in electrical knowledge, and technology.
A Wheatstone span is an electrical circuit used to mensurate an unknown electrical opposition by equilibrating two legs of a span circuit. one leg of which includes the unknown constituent. The wheatstone bridge is an instrument which is generally used to measure electrical resistance by balancing a bridge circuit.
The bridge circuit contains four resistance, one of which contains the unknown resistance,one variable resistance and two known resistance. A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component.