Amûrên Pêşewtirî Elektrîk | Tîpa Dugdemîna Rastînî Resolûsyon Vînesa

Destûrda têrê zanî û trî taypa pêşnûmara bûyera û wan hene

1. Pêşnûmara bûyera elektrîkî

2. Pêşnûmara bûyera mekanîkî.

3. Pêşnûmara bûyera elektronîkî.

Lê lêgerî da ku bi pêşnûmara bûyera elektrîkî were çêne, di navbera wan de li ser detay pir dibe. Cihên elektrîkî yekêtiya elektrîkî yên din pêşnûkirin, wek faktora elektrîkî, guher, voltage û current, y. b. Hêma cihên analogî elektrîkî bikar anîna sistemê mekanîkî ji bo pêşnûkirina yekêtiya elektrîkî yên din, lê hêma dikane ku hêma sistemê mekanîkî yên din ênîna kêm tune, cihên elektrîkî ênîna demê ya pêşnûkirina kêm tune.

Niha têrê rêzik ên hene ji bo çendkirina cihên pêşnûmara bûyera. Bi derbarê bêyî hune dikarin veqetandin:

Pêşnûmara Bûyera Absolute

Vê cihan output dide berê malperê fizîkî yên cihan. Mînak, Rayleigh’s current balance û Tangent galvanometer cihan absolute ne.

Pêşnûmara Bûyera Duyemîn

Vê cihan bikaranîna cihan absolute hatine hate çêkirin. Cihan duyemîn bi vegerastina cihan absolute hatine şopandin. Van bi piçûka cihan absolute yekêniyan bi karîna pêşnûkirina yekêtiyan, ji ber ku bi cihan absolute kar kirina demgire e.

Rêzik din ji bo çendkirina cihan pêşnûmara bûyera elektrîkî di waya ku wan neticeya pêşnûkirinê bibin. Li vir bavê wê taypa hene:

Pêşnûmara Bûyera Deflection Type

Li wan taypa cihan, pointeri cihan pêşnûmara bûyera elektrîkî deflection dide ji bo pêşnûkirina yekêti. Neticeya yekêti bi pêşnûkirina netîkê pointeri ji pozîsyona serekeya wê dide. Ji bo fahmanîna cihan deflection type permanent magnet moving coil ammeter, mînakê dibêje:

Wê şema divê du permanent magnets hebe, ku jî "stationary part" cihan ne, û "moving part" ku di navbera du permanent magnets de ye, ku jî pointeri heye. Deflection moving coil directly proportional to the current. Thus the torque is proportional to the current which is given by the expression Td = K.I, where Td is the deflecting torque.

K proportionality constant which depends upon the strength of the magnetic field and the number of turns in the coil. The pointer deflects between the two opposite forces produced by the spring and the magnets. And the resulting direction of the pointer is in the direction of the resultant force. The value of current is measured by the deflection angle θ, and the value of K.

Pêşnûmara Bûyera Null Type

Li vir bavê cihan deflection type, cihan null or zero type pêşnûmara bûyera elektrîkî tiştên pointeri statîk bibin. Wan tiştên pointeri statîk bibin bi çêkirina efektê opposing. Ji ber vê cihan null type instruments, van amarên dibêjin:

1. Qiymeta efektê opposing hewce ye ji bo pêşnûkirina qiymeta naye quantity.

2. Detector shows the balance and the unbalance condition accurately.

The detector should also have the means for restoring force.
Let us look at the advantages and disadvantages of deflection and null type of measuring instruments:

1. Deflection type of instruments is less accurate than the null type of instruments. It is because, in the null deflecting instruments the opposing effect is calibrated with the high degree of accuracy while the calibration of the deflection type instruments depends on the value of instrument constant hence usually not having high degree of accuracy.

2. Null point type instruments are more sensitive than the Deflection type instruments.

3. Deflection type instruments are more suitable under dynamic conditions than null type of instruments as the intrinsic responses of the null type instruments are slower than deflection type instruments.

Following are the important three functions of the electrical measuring instruments.

Indicating Function

These instruments provide information regarding the variable quantity under measurement and most of the time this information are provided by the deflection of the pointer. This kind of function is known as the indicating function of the instruments.

Recording Function

These instruments usually use the paper in order to record the output. This type of function is known as the recording function of the instruments.

Controlling Function

This is function is widely used in industrial world. In this topic these instruments controls the processes.
Now there are two characteristics of electrical measuring instruments and measurement systems. They are written below:

Static Characteristics

In these type of characteristics measurement of quantities are either constant or vary slowly with the time. Few main static characteristics are written below:

1. Accuracy:
   It is desirable quality in measurement. It is defined as the degree of the closeness with which instrument reading approaches the true value of the quantity being measured. Accuracy can be expressed in three ways

   
   

1. Point accuracy

2. Accuracy as the percentage of scale of range

3. Accuracy as percentage of true value.

2. Sensitivity:
   It is also desirable quality in the measurement. It is defined as the ratio of the magnitude response of the output signal to the magnitude response of the input signal.

3. Reproducibility:
   It is again a desirable quality. It is defined as the degree of the closeness with which a given quantity may be repeatedly measured. High value of reproducibility means low value of drift. Drift are of three types

   
   

1. Zero drift

2. Span drift

3. Zonal drift

Dynamic Characteristics

These characteristics are related with the rapidly changing quantities therefore in order to understand these types of characteristics we are required to study the dynamic relations between the input and the output.

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