Bar-Graph Meters

A cheap, simple kind of meter can be made using a string of light-emitting diodes (LEDs) or an LCD along with a digital scale to indicate approximate levels of current, voltage, or power. This type of meter, like a digital meter, has no moving parts to break. To some extent, it offers the relative reading feeling you get with an analog meter. Following Figure is an example of a bar-graph meter that is used to show the power output, in kilowatts, for a radio transmitter. This meter can follow along quite well with rapid fluctuations in the reading. In this example, the meter indicates about 0.8 kW, or 800 W.

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A bar-graph meter. In this case, the indication is about 80 percent of full-scale, representing 0.8 kW, or 800 W.

The chief drawback of the bar-graph meter is that it isn’t very accurate. For this reason it is not generally used in laboratory testing. In addition, the LED or LCD devices sometimes flicker when the level is between two values given by the bars. This creates an illusion of circuit instability. With bright LEDs, it can also be quite distracting.