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)