Tuesday, February 21, 2012

Analog Multimeter

Analog multimeters, although older than the commonly preferred digital multimeter, do come with several unique advantages. Although both digital and analog multimeters measure varying units, such as voltage, current, and resistance, they display their readings in distinctly different ways.

Analog multimeters can sometimes be difficult to read because they display data as a needle moving along a scale—this can be a benefit because the display of increased voltage (or resistance and so forth) is tangible, but can be hard for those unfamiliar with the scale. Like their digital counterparts, analog multimeters can measure a range of different electrical outputs, such as voltage, current, and resistance—as done with digital multimeters, a function must be selected and a corresponding range must be set. However, the way analog multimeters operate is fundamentally different than how digital multimeters operate.

Analog multimeters do take some energy from the circuit they are testing, whereas digital multimeters operate independent of circuit energy. In order to give an accurate reading analog multimeters need a high level of sensitivity—otherwise, the results may be skewed. When testing for resistance, the multimeter can rely on battery power.

Ranges for typical analog multimeter use varies with each application: For DC voltage, 0.5 V, 2.5V, 10V, 50V, 250V, 1000V are all standard range settings. For AC voltage, 10V, 50V, 250V, and 1000V are standard settings. Current is measured in amperes, with standard DC settings of 2.5, 25, and 250 amperes. AC current is hardly ever measured. Resistance, measured in ohms, has standard settings around 20, 200, 2000, 20,000, and 200,000 ohms. When not in use, leaving the multimeter around 10V is not a bad idea, because misusing the multimeter at this level is not likely to cause much damage.

Generally speaking, analog meter resistance should be ten times the circuit resistance to ensure accurate readings. A high sensitivity is necessary to prevent upsetting the test circuit. When it comes to price, a quality analog multimeter will cost about the same as a digital multimeter. Analog meters have several different options for displaying data: 

commonly a galvanometer registers movement, though sometimes a simulated pointer or bar graph is used instead. However, the width of the pointer and subsequent vibration can alter the resolution of a reading. Other common errors occur as a result of a user’s inability to read the results properly, and resistance readings tend be to especially difficult because the resistance circuit tends to cause heavy scale compression. These problems aside, however, analog meters can measure with three to five percent accuracy. Additionally, due to the galvanometer, they are often better than digital multimeters at determining the rate of change of a measurement reading. Some digital multimeters will even include a special bar graph display to strengthen this feature.

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