Laboratory 9 PDF

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Laboratory 9...

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CONSTRUCTION OF A WHEATSTONE BRIDGE

SUMMARY During the development of the laboratory, basic concepts were acquired on the use of a precision method to measure electrical resistances, in addition to the study of the equilibrium conditions of a Wheatstone bridge. A circuit was set up in which this function could be verified. We also studied the characteristics of a balanced Wheatstone bridge circuit powered by a direct current source.

INTRODUCTION Value Values measured with the calculated ohmmeter The practice carried out allowed the acquisition of knowledge about the construction of a Wheatstone bridge R1 (Ω) R3 Rx R2 Rx (Ω) Percentag as a device to convert temperature, pressure, sound, light, e error% (Ω) (Ω) (Ω) or other physical variables into electrical signals, which 1946 1943 1116 1176 1114 5.27 allow its study and measurement in a reliable way. 1946 1943 1048 1080 1046 3.14 1943 962 982 960.51 2.18 After reading the practice, he went to the laboratory to 1946 1943 713 723 711.90 1.53 check the knowledge previously learned and verify 1946 everything we had read. 2175 1943 740 675 661.06 2.06 2175 1943 594 544 530.64 2.45 Different results were obtained in which we could check 1943 429 402 383.24 4.54 the aforementioned and consult them in tables to compare 2175 the data. 1575 1943 307 380 378.73 0.33 1575 1943 239 295 294.96 0.013 1575 1943 143 166 176.41 5.15

Multiplier arm

ANALYSIS, GRAPHICS AND QUESTIONS

CONTENT

a) What parameters determine the approximation of measurements made with the experimental resistance bridge? R / The parameters that determine the approximation of the measurements are the resistance that the conductive cables oppose to the passage of the current, the own resistances that make up the bridge are subject to wear

2 and therefore to the variation of the real value of the resistance that opposes the electric current, the accuracy of the galvanometer to determine the bridge balance and the temperature variation in the laboratory. b) The results of their measurements correspond to the nominal values of the measured resistances. If not, explain the reasons why they do not match? R / From Table 1, and taking into account that the nominal values of the measured resistances are the result

of the expression , which are recorded in said table in the fifth column from the left end of it, and the values corresponding to the measurement of unknown resistance Rx reported in the fourth column from the left end of the aforementioned table measured with the professional ohmmeter, we can say that they are not the same although they are very close because in the experimental setup the different factors mentioned in point a) are not taken into account.

R / Since the resistances depend on the resistivity of the material, the length and diameter do not matter what type of current circulates through the circuit or how often it does so, since what is sought is to bring the bridge to equilibrium so that it does not exist. voltage at the ends of the galvanometer, this occurring as long as the frequency with which the current flows is not so great that the galvanometer does not deflect or that the bridge is formed based on coils or capacitors which do depend on the frequency and therefore the bridge could not be effectively stabilized. f) Express and explain different applications of bridges in science and industry? R / In science and industry, bridges are used to monitor small signals for voltage, current, frequency, and impedance.     

Dynamic bridges. Censors. Hay Bridge. Maxwell Bridge. Colpits Bridge.

c) Find the appropriate values of m and R3 to measure resistances in the range ?

R / Given the

then we can say

that , from this relationship we find that any value of m and R3 that meets the inequality works resistances in the specified range.

to

measure

d) Check what happens if instead of supplying the bridge with direct current, the source is alternating current? R / To achieve the balance of the bridge, it is not necessary that the current flowing through it be continuous since the galvanometer will deflect independently of the type of current, thus showing the point where the bridge was in equilibrium. e) Explore the consequences if the power supply signal varies with frequency, with respect to the sensitivity of the bridge?

CONCLUSIONS Thanks to the development of this laboratory it can be concluded: 

As R1 varied, resistance R3 decreased.



The resistance R1 varies, the resistance R2 remains constant and the measured resistance Rx decreases.



When calculating the resistance Rx it can be verified that it decreases.

3 

The calculated and measured Rx resistance are very similar.



To achieve bridge balance it is not necessary for the current to flow to be continuous....