Auto Range Multimeter  (220-0174A)    Features          Faxback Doc. # 7234

The Radio Shack True RMS Multimeter is a portable, 3 2/3-digit meter ideal
for field, lab, shop, bench, and home use.  The meter uses the latest IC
and display technology to achieve the lowest possible component count, and
the true RMS converter is built into a single multimeter chip.  These
features make the meter rugged and easy to use and ensure reliability,
accuracy, and stability.  Your meter also includes the following features.

        LCD Bar Graph Display - Makes nulls, peaks, and trends more
                                apparent.

    Transistor-Check Function - Measures the gain (hFE) of small-signal,
                                bipolar transistors and identifies pin-out
                                and type.

           Fully Auto-Ranging - Makes your meter easier and safer to use
                                by letting you concentrate on the probes,
                                and also lets you manually set the range
                                for situations where you know what values
                                to expert.

 Volts or dBm Voltage Display - Lets you select the unit of measure that
                                suits your application.

           Data-Hold Function - Freezes the display so you can view the
                                reading even after you disconnect the
                                leads.

          Continuity Function - Quickly checks the continuity of wires or
                                traces.

           True RMS Operation - Gives a more accurate reading for non-sine
                                wave AC measurements.

       Effective Overload and
          TransientProtection - Covers all ranges except the DC/AC 10A
                                range.

 Full Auto-Polarity Operation - Protects your meter and gives valid
                                measurements when  you connect the leads
                                in reverse polarity.

            Frequency Counter - Measures frequencies up to 2 MHz.

         Diode-Check Function - Safety checks semiconductors for open,
                                shorted, or normal junctions.

       Low-Battery Indication - Shows you when battery power is low by
                                displaying a low-battery indicator.

           Folding Wire Stand - Lets you use the meter on a bench top.

                    UL Listed - Passes the stringent tests required by
                                Underwriters Laboratories for safety.

Built-In Temperature Function - Measures temperatures from -58 degrees F
                                to 302 degrees F (-50 degrees C to 150
                                Degrees C) and gives the readings in
                                Fahrenheit (F) or Celsius (C).

Cautions:  Completely read this manual before you use the meter.

           If you are not familiar with meters and testing procedures,
           we suggest that you obtain and read a book about the subject,
           such as "Using Your Meter" (Radio Shack Cat. No. 62-2039).

WHAT DOES "TRUE RMS" MEAN?

RMS stands for Root-Mean-Square, RMS is a standard method for determining
the effective value of a varying or alternating voltage.  The RMS value
is the DC voltage that would produce the same amount of heat as the
voltage you are measuring, if you were to apply both voltage across
identical resistors.

The true RMS value is helpful when you need to measure an AC voltage that
is not a pure sine wave.  Most meters use average-responding AC
converters. These meters are calibrated with pure sine waves.  If you
measure a sine wave that does not have harmonic distortion, the meter
gives an accurate reading.  But, if the sine wave is not pure - there are
distortions within the waveform, or you measure triangle waves or square-
waves - the average - responding meters display an incorrect value.

For example, a 2-volt peak-to-peak, 50% duty cycle square wave measures
correctly as 1.000 VAC on this meter.  An average responding meter
displays 1.111 VAC - an error of more than 11 percent!

The maximum frequency your meter can accurately measure is 5000 Hz for AC
voltage and 1000 Hz for AC current.  The allowable crest factor is 1:1 to
3:1.  The crest factor is the ratio of the peak signal value divided by
the RMS value.  A 10% duty cycle square wave with a peak voltage of 3
volts has an RMS value of about .95 volts.  This gives a crest factor of
3.16 (3V/.95V), and is outside this meter's range of accuracy.

(LB/all-07/20/94)

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