Unilever has different series of industrial digital multimeters. This article mainly introduces four factors for the selection of multimeters: resolution, number of digits and words, accuracy, and true effective value.
resolution
Resolution refers to the ability of the multimeter to distinguish small signals during measurement. Knowing the resolution of the multimeter can determine whether it can observe small changes in the measured signal. If the digital multimeter has a resolution of 1mV on the 2V range, it means that it can observe a change of 1mV (1/1000V) when reading 1V. For example, if you need to measure the minimum length of 1 mm, then you will not buy a ruler with a minimum scale of 1 cm. If the normal voltage is 100.6V, then a multimeter that can only measure full amplitude is not very useful. You need a multimeter with 0.1V resolution.
digits and word count
Three and a half digits or four digits display, the first digit displays 0 or 1 (half digit), and the last three digits display 0-9. Four and a half digits are five digits display, the first digit is 0 or 1 (half digit), the last four digits are 0-9. Five and a half digits are six digits display! The first digit is 0 or 1 (half digit) and the last five The digits show 0-9. Compared with "digits", "number of words" can describe the resolution of the multimeter more accurately. Unilever multimeters provide higher resolution, three and a half digits can be divided into: 1999, 3999, 5999 and 6600 words; four and a half digits can be divided into: 19999, 22000, 39999 and 59999. Three and a half digits: the maximum number of displayed characters is 1999, and the resolution is 1/2000 of the range; four and a half digits: the maximum number of displayed characters is 19999, and the resolution is 1/20000 of the range; five and a half digits: the maximum number of displayed characters is 199999, and the resolution is 1/20000 of the range 1/200000 of the range.
Accuracy
Accuracy refers to the maximum error between the measured value and the true value under certain conditions. In other words, accuracy indicates how close the multimeter's measurement is to the actual value of the signal being measured. The accuracy of a digital multimeter is usually expressed as a percentage of reading. An accuracy of 1% of reading means that if the measured value is 100V, the actual displayed value could be anywhere between 99V and 101V. Specifications also include a bit range (last bit) that is added to the basic precision parameter. For example, the accuracy is expressed as: ±(1%+2), so if the test voltage is 100V, the actual displayed value will be between 98.8 and 101.2V.
True RMS
True RMS: The effective expression of abnormal AC signals is obvious. People are most concerned about the true RMS, but it is not easy to measure, and the average value and peak value are easy to measure, so ordinary multimeters use the method of measuring the average value or peak value. Indirect measurement of effective value (according to the relationship of sine wave). For example, if the peak value is measured by an instrument, if the measured value is 10V, it will be displayed as 7.07V (effective value). These two types of meters display effective values, but they measure "false" effective values. Obviously, it is relatively accurate to use this type of meter to measure sine waves, but it is wrong to measure non-sine waves. The true RMS multimeter can accurately and real-time measure the RMS of various voltage waveforms without considering the waveform parameters and distortion. These performances are unmatched by the average meter.
