Digital Multimeters/Clamp Meters/Voltage and Continuity Testers


Glossary - Multimeters RMS


Root Mean Square. When an AC supply is placed onto a circuit, it produces heat. The RMS value is the equivalent DC supply that would produce the same amount of ther- mal heat as the actual AC supply.


True RMS A specifi c method of measuring the RMS value of a signal. With inductive and capacitive systems distorting the sinusoidal wave of the mains supply, this method provides the most accurate RMS value regardless of the shape of the waveform. Other methods of measuring rms values exist, such as the rectifi er or mean absolute deviation method; however, these methods are accurate only for sine wave signals.


Crest factor


The crest factor describes the ratio of the peak value to the RMS value of an electrica variable (AC voltage and AC current).


High crest factors cause distor- tion reactive power and harmonics in the supply network, and so are undesirable.


With high crest factors, electronic instruments often display inexact values. This must be considered when selecting an instrument. For example, if an instrument measures 20 A AC current, the peak value is around 28 A with a sinusoidal wave- form. So the instrument must be able to handle much higher peak currents than the RMS value.


Number of Counts


The number of divisions into which a given measurement range is divid- ed. This can be used to evaluate the resolution of an instrument


Accuracy


A value to show how accurately an instrument can read a specifi c value. This is usually written as a percent- age (e.g. 5 V ± 5 %)


7. 2


CAT IV 1000 V


Safety category RCD RCD trip-out test R 3 A 3 years


manufactures waranty


Phase rotation indication


Resolution


The smallest possible change in a signal that would produce a change in the value on the screen of the test instrument


Overvoltage category CAT the overvoltage category speci- fi es the highest mains voltage (or lightning strike, short circuit due to incorrect use; etc.) that the instru- ment can withstand without danger for the tester or for the object being measured. The standard specifi es four overvoltage categories. The overvoltage category affects com- ponent sizing via the air gap. The higher the category, the bigger is the distance to the power source.


CAT I


Electronic devices, signal level, CAT II


Domestic appliances, portable appli- ances, single-phase loads, sockets, (>10 m from CATIII; >20 m from CAT IV),


CAT III


Three-phase distribution systems, lighting systems in large buildings, distribution panels,


CAT IV


Three-phase systems on power sta- tions, electricity meters, outdoor installations and supply cable incom- ing feed


Digital Multimeters/Clamps metres/Voltage testers


THD THD measurement W Power Power measurement Jaw 28 mm Jaw size PC Link


TRMS True RMS measurement


EF


Non contact voltage detection


Auto- check


Automatic V / Ω measurement


°C


Temperature measurement


50th Harm


Harmonic analysis


Accessories: page 7.19


W


A


N


R


R


E A


T


Y


S


Y


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