<P> Modern galvanometers, of the D'Arsonval / Weston type, are constructed with a small pivoting coil of wire in the field of a permanent magnet . The coil is attached to a thin pointer that traverses a calibrated scale . A tiny torsion spring pulls the coil and pointer to the zero position . </P> <P> When a direct current (DC) flows through the coil, the coil generates a magnetic field . This field acts against the permanent magnet . The coil twists, pushing against the spring, and moves the pointer . The hand points at a scale indicating the electric current . Careful design of the pole pieces ensures that the magnetic field is uniform, so that the angular deflection of the pointer is proportional to the current . A useful meter generally contains provision for damping the mechanical resonance of the moving coil and pointer, so that the pointer settles quickly to its position without oscillation . </P> <P> The basic sensitivity of a meter might be, for instance, 100 microamperes full scale (with a voltage drop of, say, 50 millivolts at full current). Such meters are often calibrated to read some other quantity that can be converted to a current of that magnitude . The use of current dividers, often called shunts, allows a meter to be calibrated to measure larger currents . A meter can be calibrated as a DC voltmeter if the resistance of the coil is known by calculating the voltage required to generate a full scale current . A meter can be configured to read other voltages by putting it in a voltage divider circuit . This is generally done by placing a resistor in series with the meter coil . A meter can be used to read resistance by placing it in series with a known voltage (a battery) and an adjustable resistor . In a preparatory step, the circuit is completed and the resistor adjusted to produce full scale deflection . When an unknown resistor is placed in series in the circuit the current will be less than full scale and an appropriately calibrated scale can display the value of the previously unknown resistor . </P> <P> These capabilities to translate different kinds of electric quantities, in to pointer movements, make the galvanometer ideal for turning output of other sensors that outputs electricity (in some form or another), into something that can be read by a human . </P>

When is a galvanometer said to be sensitive