Hardware Reference
In-Depth Information
Usually, each system-unit measurement setting has several ranges of operation. DC
voltage,forexample,usuallycanbereadinseveralscales,toamaximumof200millivolts
(mV),2V,20V,200V,and1,000V.Becausecomputersuseboth+5Vand+12Vforvarious
operations,youshouldusethe20Vmaximumscaleformakingyourmeasurements.Mak-
ing these measurements on the 200mV or 2V scale could “peg the meter” and possibly
damage it because the voltage would be much higher than expected. Using the 200V or
1,000Vscaleworks,butthereadingsat5Vand12Varesosmallinproportiontothemax-
imum that accuracy is low.
If you are taking a measurement and are unsure of the actual voltage, start at the highest
scale and work your way down. Most of the better meters have autoranging capabil-
ity—the meter automatically selects the best range for any measurement. This type of
meter is much easier to operate. You simply set the meter to the type of reading you want,
such as DC volts, and attach the probes to the signal source. The meter selects the cor-
rect voltage range and displays the value. Because of their design, these types of meters
always have a digital display rather than a meter needle.
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