Cikin Yaki na Kelvin | Cikin Yakin Dabam na Kelvin
Idan da na ba da Kelvin Bridge, yana da kyau a bayyana abin da wannan bridge ya fi kyau. Amma akwai Wheatstone bridge wanda ya iya bincike kamar daidaito mai girgiza (karkashin zama 0.1%).
Don in fahimta abin da ke neman da ake yi da Kelvin bridge, muna bukata da sauka masu muhimmanci na tattalin girgizar kamar:
Girgizar Kamar Da Gaba: Girgizar kamar da gaba da 0.1 Mega-ohm.
Girgizar Kamar Na Farko: Girgizar kamar daga 1 ohm zuwa 0.1 Mega-ohm.
Girgizar Kamar Daji: Tana da girgizar kamar da yake da daraja mai kadan da 1 ohm.
Yanzu, saboda hakan, idan an samun girgizar kamar, muna bukata da alatun da ake amfani da shi don kada girgizar kamar. Yana cewa idan alatun da ake amfani da shi don kada girgizar kamar da gaba ya ba da tsarin da za a yi, yana iya ko bai iya ba da tsarin da za a yi a kada girgizar kamar da daji.
Saboda haka, muna bukata da ilimi da lura don in fahimta wadanda suka amfani da shi don kada girgizar kamar da kuma ma'anar daidaito. Amma akwai wasu tarihi da suka amfani da su kamar tarihin ammeter-voltmeter, substitution method, kamar haka, amma suna ba da dole daidai da tarihin bridge.
Idan nan zo ne a duba tattalin da ake yi da shi, idan an yi nasara da girgizar kamar da daji, muna bukata da alatun da ya fi kyau da ya fi tsari don kada shi.
Daga cikin abubuwan da ke neman da ake yi da Wheatstone bridge ta, musamman idan an yi kada girgizar kamar da daji, yana ba da dole daidai.
Saboda haka, muna bukata da some modification a Wheatstone bridge, kuma bridge da aka samu shine Kelvin bridge, wanda ya fi kyau don kada girgizar kamar da daji, kuma ya fi karatu da yake amfani da shi a rayuwar industries.
Za a hada da wasu kalmomi da za su taimakawa wajen fahimtar Kelvin Bridge.
Bridge :
Bridges suna da sida arms to furu, balance detector da source. Suna yi waɗannan waɗanda suka haɗa da null point technique. Suna da kyau a fayacewa tun daga baya saboda babu lafiya da ake yi don in meter ya fi tsari da scale. Babu lafiya da ake yi don in ake kada voltage da current, kawai ake buƙata da presence or absence of current or voltage. Amma abin da ke neman da ake yi shine idan an yi null point, meter ya fi kyau don in ya iya pick up fairly small current. A bridge zan iya bayyana shi da voltage dividers a parallel and the difference between the two dividers is our output. Yana da kyau a kada components like girgizar kamar, capacitance, inductor and other circuit parameters. Accuracy of any bridge is directly related to bridge components.
Null point:
Yana iya bayyana shi da point inda null measurement occurs when the reading of ammeter or voltmeter is zero.
Kelvin Bridge Circuit
Idan an samun cewa Kelvin Bridge ita ce modified Wheatstone bridge and provides high accuracy especially in the measurement of low resistance. Yanzu, wato da za a faru a kan minda muna bukata da where do we need the modification. Amsa da za a faru shine very simple – it is the portion of leads and contacts where we must do modification because of these there is an increment in net resistance.
Let us consider the modified Wheatstone bridge or Kelvin bridge circuit given below:
Here, t is the resistance of the lead.
C is the unknown resistance.
D is the standard resistance (whose value is known).
Let us mark the two points j and k. If the galvanometer is connected to j point the resistance t is added to D which results in too low a value of C. Now we connect galvanometer to k point it would result in a high value of unknown resistance C.
Let us connect the galvanometer to point d which is lying in between j and k such that d divides t into ratio t1 and t2, now from the above figure it can be seen that
Then also the presence of t1 causes no error, we can write,
Thus we can conclude that there is no effect of t (i.e. the resistance of leads). Practically it is impossible to have such situation however the above simple modification suggests that the galvanometer can be connected between these points j and k so as to obtain the null point.
Kelvin Double Bridge
Why it is called double bridge? It is because it incorporates the second set of ratio arms as shown below:
In this the ratio arms p and q are used to connect the galvanometer at the correct point between j and k to remove the effect of connecting lead of girgizar kamar t. Under balance condition voltage drop between a and b (i.e. E) is equal to F (voltage drop between a and c)
For zero galvanometer deflection, E = F
Again we reach the same result – t has no effect. However equation (2) is useful as it gives error when:
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