History and Theory of the Wheatstone Bridge A Wheatstone bridge is a measuring instrument invented by Samuel Hunter Christie in 1833 and improved and popularized by Sir Charles Wheatstone in 1843. It is 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 except that in potentiometer circuits the meter used is a sensitive galvanometer. Here, Rx is the unknown resistance to be measured; R1, R2 and R3 are resistors of known resistance and the resistance of R2 is adjustable. If the ratio of the two resistances in the known leg (R2 / R1) is equal to the ratio of the two in the unknown leg (Rx / R3), then the voltage between the two midpoints will be zero and no current will flow between the midpoints. R2 is varied until this condition is reached. The current direction indicates if R2 is too high or too low. Detecting zero current can be done to extremely high accuracy . Therefore, if R1, R2 and R3 are known to high precision, then Rx can be measured to high precision. Very small changes in Rx disrupt the balance and are readily detected. If the bridge is balanced, which means that the current through the galvanometer Rg is equal to zero, the equivalent resistance of the circuit between the source voltage terminals is: R1 + R2 in parallel with R3 + R4 Alternatively, if R1, R2, and R3 are known, but R2 is not adjustable, the voltage or current flow through the meter can be used to calculate the value of Rx, using Kirchhoff's circuit laws. This setup is frequently used in strain gauge and Resistance Temperature Detector measurements, as it is usually faster to read a voltage level off a meter than to adjust a resistance to zero the voltage. First, we can use the first Kirchhoff rule to find the currents in junctions B and D: Then, we use Kirchoff's second rule to find the voltage in the loops ABD and BCD: The bridge is balanced and Ig = 0, so we can rewrite the second set of equations: Then, we divide the equations and rearrange them, giving: From the first rule, we know that I3 = Ix and I1 = I2. The desired value of Rx is now known to be given as:
“It was designed with a twenty-two foot roadway and one five-foot sidewalk” (Silver). The silver bridge is a very long bridge. “An eye-bar is a long steel plate having large circular ends with an "eye" or hole through which a pin is used to connect to other eyebars (to make a chain) or to other parts of the bridge.” according to Richard Fields. The whole bridge was built using the eye-bar suspension.
(t)| (12) The −→ A , −→ C vectors are calculated as in equations 13 and 14 −→ A = 2 −→ A . −→ r 1 − −→ a (13)
Oscilloscope is acquainted as one of the most helpful instrument for testing circuits. It is able to show the signals at different points in the circuit. One way to inves...
I found that in grid 5x5 that the formula for the added value of the
Assuming that x2 = 20 basis, and x1 = 100 basis. We can conclude the
resistance and blood volume. Cardiac output refers to the amount of blood pumped by the heart
Below the graph consist of the intersections of the line ‘y = x’ , ‘y = 2x’ with the curve y = x4
3. Why are the crucible and lid heated at the beginning of the experiment before being weighed?
• For this particular experiment the gain of the output for the strain gauges are set to 1 as 0 to 8 degrees slip angle is been measured. If smaller angles are measured a larger gain may be required.
Basic Mathematics for Electronics seventh edition: Nelson M. Cooke, Herbert F.R Adams, Peter B. Dell, T. Adair Moore; Copyright 1960
Inversely, to decrease I, R must increase. The value of R depends on how easy it is for the electric charge to pass through the conductor. Therefore to decrease R, the passage must be made easier and to
For this bridge its fall was inflicted by an unknown patron. One who’s identity or existence we never see verified. The record of the fall is short in the story described as only being for a moment. Then the bridge was finally introduced to “the sharp rocks which had always gazed up at me so peacefully from the rushing water”. Rocks gazing peacefully? This is almost as absurd as a bridge turning around. An action that the bridge itself cannot seem to believe it is doing. This attempt by the bridge was his final effort before his fall. I cannot even picture how a bridge would turn around and attempt to look on his back. The question that comes to my mind is how can a bridge see what’s on his back? If this book is trying to make us believe that this bridge is a human, or has human like qualities. Then how flexible a person is this bridge? Because I know very few people who can see whats on their back. Especially without turning so much that anything on their back would fall off. So is this bridge so inflexible that it breaks itself by turning around or is it trying to buck off its attacker unintentionally? This answer is never answered due to the story ending shortly thereafter this scene. With the short fall of the bridge onto the sharp rocks it had stared at for the entirety of its life. The events before and during the fall of the bridge was the main issue I had with my thesis that the bridge was
There are formulas to calculate electrical conductivity and resistivity. Conductivity (s) is defined as the inverse of resistivity (a high conductivity means a low resistance), I=V/R or current equals voltage over resistance. Electrical resistance is calculated by the formula, R=V/I or resistance equals voltage over current.