This slide suggests that a low resistance indicates a good fuse, and high resistance a bad fuse, but doesn't give a baseline for what is low vs high. What range should my ammeter be reading when I test it for continuity?
why do the resistors are connected in series with the D'arsonval galvanometer for voltage measurement, and connected in parallel for current measurement??? If you have the answer, please do reply. Its really urgent...
Ammeter and Galvanometer
An ammeter is a measuring instrument used to measure the electric current in a circuit.
Electric currents are measured in amperes (A), hence the name.
Instruments used to measure smaller currents, in the milliampere or microampere range, are designated as milliammeters or microammeters.
Early ammeters were laboratory instruments which relied on the earth's magnetic field for operation.
By the late 19th century, improved instruments were designed which could be mounted in any position and allowed accurate measurements in electric power systems.
A galvanometer is a type of ammeter, which is an instrument for detecting and measuring electric current.
It is an analog electromechanical transducer that produces a rotary deflection of some type of pointer in response to electric current flowing through its coil in a magnetic field.
The commonly used sensing-mechanism in DC ammeters, voltmeters, and ohmmeters is a current-sensing device called a D’Arsonval meter movement.
The D’Arsonval movement is a DC moving coil-type movement in which an electromagnetic core is suspended between the poles of a permanent magnet.
Moving-Coil Meters – How they Operate
A moving-coil meter movement operates on the electromagnetic principle.
The process for this type of moving meter is listed below:
• A coil of very fine wire wound on a light aluminum frame.
• A permanent magnet surrounds the coil.
• The aluminum frame is mounted on pivots to allow it and the coil to rotate freely between the poles of the permanent magnet.
• When current flows through the coil, it becomes magnetized, and the polarity of the coils is repelled by the field of the permanent magnet.
• This causes the coil frame to rotate on its pivots, and the distance it rotates is determined by the amount of current that flows through the coil.
• By attaching a pointer to the coil frame and adding a calibrated scale, the amount of current flowing through the meter can be measured.
• Multiplier resistors are used to extend the range of the meter movement for voltage measurements, while shunt resistors are used to extend the range of the meter movement for current measurements.
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