Pointer meters, whether used to measure voltage, current, resistance, frequency, level, temperature or humidity, are based on some common operating principles. These principles mainly include:
1.Electromagnetic principle.
Ammeters and voltmeters: These instruments are often based on the electromagnetic effect, in which an electric current through the instrument creates a magnetic field that interacts with a permanent magnet to turn the pointer. An ammeter measures the current directly through the instrument, while a voltmeter measures the voltage difference at a lower current with a built-in high impedance that allows it to operate at a lower current.
Resistance Meter: A resistance meter typically uses a simple bridge circuit in which the resistance to be measured is compared to a known resistance to determine the value of an unknown resistance by measuring the difference in the current passing through the bridge. The deflection of the pointer provides a direct reading of the resistance value.
2.Heating.
Thermometers: Some types of analogue thermometers use bimetal strips, which are bands of two different metal materials that expand at different rates. When the temperature changes, the bimetal strip bends, driving the pointer to move. Another method is to use the voltage generated by the thermocouple to drive the electromagnetic pointer.
3.Mechanical effects.
Frequency Meters and Level Meters: These instruments may use the principle of mechanical resonance, in which a part of the instrument, such as a spring or oscillating part, resonates when it matches the frequency of the measured signal, driving the pointer through mechanical motion.
Hygrometer: An analog hygrometer typically uses a single curl of artificial or natural hair, the length of which varies with relative humidity. The hair's telescopic drive pointer shows humidity readings.
4.Stress effects.
In some cases, such as some special temperature gauges, a closed system filled with liquids or gases may be used, where a change in temperature causes a change in internal pressure, which in turn drives the pointer through a system of mechanical levers.
Although these measuring devices use different sensors and principles when measuring different physical quantities, they all share a core concept: to convert the measured physical quantity into some form of energy (electrical, mechanical, etc.) and then use this energy to drive the pointer, which is deflected at an angle proportional to the physical quantity being measured. This makes the readings intuitive and easy to understand.