- Technical Blog From My Notebook

Sunday, June 19, 2016

Digital readout meters-principle and operation


Increasingly, metering devices are being designed so that they provide a direct readout, and theres no need (or possibility) for interpolation. The number on the meter is the indication.Its that simple. Such a meter is called a digital meter.
The advantage of a digital meter is that its easy for anybody to read, and there is no chance for interpolation errors. This is ideal for utility meters, clocks, and so me kinds of ammeters, voltmeters and wattmeters. It works very well when the value of the quantity does not change very often or very fast.
But there are some situations in which a digital meter is a disadvantage. One good example is the signal-strength indicator in a radio receiver. This meter bounces up and down as signals fade, or as you tune the radio, or sometimes even as the signal modulates.
A digital meter would show nothing but a constantly changing, meaningless set of numerals. Digital meters require a certain length of time to lock in to the current, voltage, power or other quantity being measured. If this quantity never settles at any one value for a long enough time, the meter can never lock in.
Meters with a scale and pointer are known as analog meters. Their main advantages are that they allow interpolation, they give the operator a sense of the quantity relative to other possible values, and they follow along when a quantity changes. Some engineers and technicians prefer the feelof an analog meter, even in situations where a digital meter would work just as well.
One problem you might have with digital meters is being certain of where the decimal point goes. If youre off by one decimal place, the error will be by a factor of 10.

Also, you need to be sure you know what the units are; for example, a frequency indicator might be reading out in megahertz, and you might forget and think it is giving you a reading in kilohertz. Thats a mistake by a factor of 1000. Of course this latter type of error can happen with an analog meter, too.

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