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TOPIC 4

TOPIC 4. C 1. C 2. I C1 = I C2 = I C3 = I. C 3. Current balance. I C1 enters C 1 at the bottom and leaves it at the top, I C2 enters C 2 at the top and leaves it at the bottom. 

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TOPIC 4

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  1. TOPIC 4

  2. C1 C2 IC1 = IC2 = IC3 = I C3 Current balance IC1 enters C1 at the bottom and leaves it at the top, IC2 enters C2 at the top and leaves it at the bottom.   Electromagnetic forces on the suspended coil, produced by these two currents, are of the same sense.

  3. Current balance

  4. Current balance

  5. Current balance operation • The mass of the suspended coil plus the vertical electromagnetic force exerted on it are counterbalanced by means of a mass m on the left scale pan. • After reversing the current in the suspended coil, the change m of this mass, necessary to offset the change F of the acting electromagnetic force, is determined.

  6. Current balance operation A separate moving experiment makes it possible to avoid the troublesome calculation of f from the dimensions of the coils: Coil C3, which is threaded by the magnetic flux produced by the current I flowing in C1 and C2, is moved with a constant velocity v in the vertical direction, a voltage u(t) being induced in it:

  7. Current balance operation If a voltage drop U = R I isproduced by the current I on a known resistance R and if a velocity v is choosen for which in the moment of passage of the scale beam through its equilibrium position,

  8. Electronic kilogram In case that quantum standards of voltage and resistance are used to measure the current I flowing in the coils in course of the weighing experiment, a current balance with a known value of f can be used to produce known values of electromagnetic force and to monitor variations of masses which are used to counterbalance it.

  9. Voltage balance is an apparatus based on counterbalancing the attractive force between electrodes of a capacitor.

  10. Is Ip Constant current PS Slave PS R Ux, Ue Ns ns Np PD Ns = 1000 turns OSC ns =  11 turns in steps of 10-4 turns Np 2000 turns, steps of 10-4 turns DC comparator potentiometer

  11. SPS Is ... 500 50 Ω Ω 5.625 Ω 1turn/step R 1000 turns Realization of the equivalentof fractional turns

  12. Primary voltage standard system with closed-cycle refrigerator

  13. Primary voltage standard system with closed-cycle refrigerator • 100 nV calibration accuracy • -11 V to 11 V range available from 10-V system • typically 1 hour stability time at 10 V for 10-V system • automatic voltage calibration in minutes • automatic calibration of DVMs • complete system diagnostics

  14. 1 2 S1 S2 Rs1 Rs2 Ux Ur TE1 R TE2 RMS/DC thermocouple comparator

  15. Ux Ur Rs1 Rs2 TE1 TE2 Automatic RMS/DC thermocouple comparator

  16. to relay R drives A R R to relay R drives A Thermocouple protection

  17. Ua R1 R2 Ur A Rs1 T1 T2 Ux Rs2 RMS/DC thermistor comparator

  18. Ua R1 R3 R2 Ur A1 A2 Rs1 Rs2 Ux R4 T1 T2 Improved RMS/DC thermistor comparator

  19. moving coil ic1 ic1 ic2 fixed coils Electrodynamic method of measurement of AC power ic1=i1 + I1 ic2=i2 - I2

  20. Uout Ur I1 I2 Control circuit R R ic1 ic2 electrodynamometer R R uI uU i2 i1 A2 A1 fixed coils moving coil Electrodynamic method of measurement of AC power i1

  21. uU Uout R R R R A4 A2 A1 R R R R uI A3 Thermal wattmeter

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