Wattmetrê Elektrodinamometrik

Taybetîna Elektrodinamometre Wattmetreyê

Wattmetreyên cûr a elektrodinamometre çendiyê di navbera sazên magnetîk û derzanên elektrik de pêşkeftina serokirina nîrgirtiyê.

Sernivîs Pêşkeftina

Hêro bitem bi vebijarkên taybetî yên wattmetreyê ya elektrodinamometre. Ew ji wan parçeyên de veqetand:Divê yekem sargirdan ên coil an sazên hêsan di wattmetreyê da ye. Wan hin:

Coil Bihêviyê

Coil bihêviyê bi alîkarîya amûraya kontrolê ya springê peyserên pençereyê biguherîne. Ji bo danasîn lêzerd bike, derzê meheng a di navbera coil bihêviyê de hatine guherandin. Coil bihêviyê li pivoted spindle destnîşan e u dikare be weraz bikatîne. Di wattmetreyên cûr a elektrodinamometrede, coil bihêviyê wek coil presyonê hatine guhert u bi serka gerîyan hatine guherandin, ta dibawa derza wê bi geriya proporsiyonal bibe.

Coil Peyser

Coil peyser divê du parçeya herêmî yên wekhevi hatine jixwekirin u li ser îlka dabeşand, dema ku derza îlka di wan coils de bigerîne. Arazê bêtir bi rastî ne ku divê du coils peyser bane, ta ew biafirîne ku bibeke bike bi pir ber derzan elektrik. 

Ew coils jî wek current coils an coils derzanên wattmetreyên cûr a elektrodinamometre ne. Piştî wan coils peyser hatine dizayn kirin bi tenê 100 amper, ema wattmetreyên modern hatine dizayn kirin bi tenê 20 amper di navbera hilanîna nîrgirtiyê de.

Sistem Kontrol

Ji du sistemên kontrolan, yekem:

Kontrol Gewr

Kontrol spring, tenê sisteman kontrol spring di wan cûrên wattmetreyan de hatine bikar bînin. Sistem kontrol gewr nayê bikar bînin çünki hewce ye ku hata zor bibe.

Sistem Damping

Damping air friction hatine bikar bînin çünki damping eddy current dikare sazên magnetîk operasyonan zêde bibin, ku heta xeta bibin.

Scale uniform hatine bikar bînin di wan cûrên instrumentan de, çünki coil bihêviyê li ser range 40 dergeze heta 50 dergeze di her du taraf de linî biberdarê.

Hêro bitem bi rêzikên torque kontrol u deflection. Ji bo derîva wan rêzik, bitem bi şema circuit di vir:

Biz bînim ku torque instantaneous di instrumentan electrodynamican de tuha bi producti instantaneous values of currents flowing through both the coils u rate of change of flux linked with the circuit.

I1 u I2 instantaneous values of currents in pressure and current coils respectively. So the expression for the torque can be written as:

Lêkê, x angle ye.

Niha value applied voltage across the pressure coil be

Ji ber electrical resistance of the pressure coil being very high, biz reaktans compared to its resistance neglekte bikin. Thus, impedance is equal to its electrical resistance, making it purely resistive.

Expression for instantaneous current can be written as I2 = v / Rp where Rp is the resistance of pressure coil.

If there is phase difference between voltage and electric current, then expression for instantaneous current through current coil can be written as

As current through the pressure coil is very very small compared to the current through current coil hence current through the current coil can be considered as equal to total load current.Hence the instantaneous value of torque can be written as

Average value of deflecting torque can be obtained by integrating the instantaneous torque from limit 0 to T, where T is the time period of the cycle.

Controlling torque is given by Tc = Kx where K is spring constant and x is final steady state value of deflection.

Advantages

• Scale is uniform upto a certain limit.

• They can be used for both to measure ac as well dc quantities as scale is calibrated for both.

Errors

• Errors in the pressure coil inductance.

• Errors may be due to pressure coil capacitance.

• Errors may be due to mutual inductance effects.

• Errors may be due connections.(i.e. pressure coil is connected after current coil)

• Error due to Eddy currents.

• Errors caused by vibration of moving system.

• Temperature error.

• Errors due to stray magnetic field.