True RMS Multimeter  (220-0175A)     Features          Faxback Doc. # 7241

This Micronta True RMS Multimeter is a portable 3 2/3-digit, meter ideally
suited for field, lab, shop, bench, and home use.  It makes true RMS
measurements, a feature you normally find only in the most expensive test
instruments, so AC measurements are as accurate as possible.  Here are
some features that make the meter a real pro.

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

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

    Capacitor-Check Function - measures the capacitance of low-voltage
                               capacitors.

           Frequency Counter - measures frequencies up to 2 MHz.

One-Finger Function Selector - makes it easy to use your meter when you
                               have only one hand free.

A WORD ABOUT SAFETY

We have taken every precaution in designing this meter to ensure that it
is as safe as we can make it.  But, safe operation depends on you, the
operator.  We recommend that you follow these simple safety rules:

  Never apply voltages to the meter that exceed the limits given in the
  specifications.  Never apply more than 1000V DC or 750V RMS AC between
  any input terminals or between an input terminal and ground.

  Use extreme caution when you work with voltages above 40V.  Always
  disconnect power from the circuit you are measuring before you connect
  test probes to high-voltage points.

  Never connect the test probes to a source of voltage when you select the
  diode, ohms, continuity, current measurement, capacitance, or hFE
  functions.

  Always  discharge filter capacitors in the power supply of the circuit
  under test before you attach test probes.

  Always turn off the meter's power and disconnect the test leads before
  you replace the batteries or fuse.

  Never operate the meter unless the battery cover is in place and fully
  closed.

  Because many AC/DC sets have a potentially hot chassis, be sure the top
  of your workbench and the floor underneath it are made of non-conductive
  materials.

The multimeter is fully calibrated and tested.  Under normal use, no
further adjustment should be necessary.  If the meter should require
repair, do not try to adjust it yourself.  Take it to your nearest Radio
Shack store.  Service by unauthorized personnel voids the warranty.

WARNING:  USE EXTREME CAUTION IN USE OF THIS DEVICE.  IMPROPER USE OF THIS
          DEVICE CAN RESULT IN INJURY OR DEATH.  FOLLOW ALL SAFEGUARDS
          SUGGESTED IN THE OWNER'S MANUAL IN ADDITION TO NORMAL SAFETY
          PRECAUTIONS IN DEALING WITH ELECTRICAL CIRCUITS.  DO NOT USE
          THIS DEVICE IF YOU ARE UNFAMILIAR WITH ELECTRICAL CIRCUITS AND
          TESTING PROCEDURES.  NOT FOR COMMERCIAL OR INDUSTRIAL USE.

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 voltages 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
32:1.  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.

(br/all-7/21/94)