Test Instruments & Measuring DevicesMETER MOVEMENTSMovingIronVaneMovementThe moving iron vane movement (Figure 3) can be used to measure both AC current and voltage.By changing the meter scale calibration, the movement can be used to measure DC current andvoltage. The moving iron vane meter operates on the principle of magnetic repulsion betweenlike poles. The measured current flows through a field coil which produces a magnetic fieldproportional to the magnitude of current. Suspended in this field are two iron vanes attached toa pointer. The two iron vanes consist of one fixed and one moveable vane. The magnetic fieldproduced by the current flow magnetizes the two iron vanes with the same polarity regardlessof the direction of current through the coil. Since like poles repel one another, the moving ironvane pulls away from the fixed vane and moves the meter pointer. This motion exerts a forceagainst a spring. The distance the moving iron vane will travel against the spring depends onthe strength of the magnetic field. The strength of the magnetic field depends on the magnitudeof current flow.Figure 3 Moving Iron Vane Meter MovementAs stated previously, this type of meter movement may also be used to measure voltage. Whenthis type of movement is used to measure voltage, the field coil consists of many turns of finewire used to generate a strong magnetic field with only a small current flow.Rev. 0 Page 3 ES-14
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