An introduction to digital multimeter technical indicators
Your needs can be satisfied and even exceeded by digital multimeters. Simple to use, just needs one hand to operate, and can be flexible enough to be used while wearing gloves.
Digital multimeter technical indicators
Numbers on the display and its features
A digital multimeter's display digits typically range from 31/2 to 81/2 digits. There are two guidelines for evaluating a digital instrument's display digits:
One is that integer digits are the only ones capable of displaying all numbers from 0 to 9;
The instrument has three integer digits, and the numerator of the fractional digit is 1, and the denominator is 2, so it is called 31/2 bits, which is read as "three and a half digits," and its highest bit can only display 0 or 1. The second is that the numerical value of the fractional digit is the numerator of the highest digit in the maximum display value, and the count value is 2000 when the full scale is used.
The maximum display value is 2999 because the top digit of a 32/3-digit (pronounce "three and two-thirds") digital multimeter can only show digits from 0 to 2. It is 50% higher than a 31/2-digit digital multimeter's upper limit under the identical circumstances, which is useful when measuring 380V AC voltage.
For instance, a standard 31/2-digit digital multimeter's highest digit can only be 0 or 1 when used to measure grid voltage. You can only use three digits to display grid voltage when measuring 220V or 380V. This file only has a 1V resolution.
The topmost digit of a 33/4-digit digital multimeter, however, can only display 0 to 3, making it possible to display the grid voltage in four digits with a resolution of 0.1V, the same as a 41/2-digit digital multimeter.
Popular digital multimeters typically fall into two categories: portable and desktop. Handheld multimeters with a 31/2 digit display are the most common, while digital multimeters with displays of 41/2 and 51/2 digits (below 6 digits) are also popular. Most desktop digital multimeters have more than 6 1/2 digits.
The digital multimeter uses cutting-edge digital display technology, providing a clear, user-friendly display and precise readings. It not only conforms to readers' reading preferences and ensures the objectivity of the reading, but it can also cut down on reading or recording time. These benefits aren't offered by conventional analog (i.e. pointer) multimeters.
2. Accuracy (precision)
The sum of systematic errors and random errors in the measurement results is the accuracy of a digital multimeter. It reflects the size of the measurement error as well as the degree of agreement between the measured value and the true value. Generally speaking, the smaller the measurement error, the higher the accuracy, and vice versa.
The accuracy can be expressed in one of the following three ways:
Accuracy = ± (a%RDG+b%FS) (2.2.1)
Accuracy = ± (a% RDG + n words) (2.2.2)
Accuracy = ± (a%RDG+b%FS+n words) (2.2.3)
In the formula (2.2.1), RDG stands for the reading value (also known as the display value), FS for the full-scale value, and the previous item in brackets for the A/D converter and functional converter (such as voltage divider, shunt, or true effective value converter), the latter of which is the digitization error, are all represented.
The amount of change indicated by the last digit of the quantization error is denoted by the symbol n in formula (2.2.2). The formula is the mistake of n words expressed as a percentage of the complete scale (2.2.1). The formula (2.2.3) is quite unique. This expression is used by some manufacturers, and one of the last two items stands for the error brought on by other environments or functions.
Digital multimeters have far higher accuracy than analog multimeters do. As an illustration, the accuracy index of the basic range for measuring DC voltage can be as high as 0.5% with 3 and a half digits and as low as 0.03% with 4 and a half digits.
Multimeters like the OI857 and OI859CF, for instance. A crucial indicator is the multimeter's accuracy. It displays the multimeter's performance and process capability. A multimeter with poor accuracy finds it challenging to express the true value, which can easily lead to measurement errors.
3. Resolution (resolution)
Resolution, which represents the sensitivity of the meter, is the voltage value that corresponds to the last digit of the digital multimeter on the lowest voltage range.
As the number of display digits rises, so does the resolution of digital instruments. The highest resolution indicators that digital multimeters with various digit counts can achieve vary, for instance: 100V for a multimeter with 31/2 digits.
The digital multimeter's resolution index can also be shown by resolution. Resolution is the ratio of the meter's smallest possible number (other than zero) to its largest possible number.
For instance, a standard 31/2-digit digital multimeter can display a minimum of 1 and a maximum of 1999, meaning that the resolution is 1/19990.05%.
It is important to note that resolution and accuracy are two distinct ideas. The former reflects the "accuracy" of measurement, which is the degree of consistency between the measurement result and the true value; the latter reflects the instrument's "sensitivity," which is its capacity to "recognize" minute voltages.
The resolution (or resolution) should not be mistaken for similarity because there is no necessary connection between the two, making it impossible to mix them up. The internal A/D converter and instrument's functional converter's comprehensive error and quantization error determine the instrument's accuracy.
Resolution is a "virtual" indicator in the sense that it has nothing to do with measurement error, whereas accuracy is a "real" indicator. In order to increase the instrument's resolution, it is therefore not possible to arbitrarily increase the number of display digits.
4. Measuring range、
In a multi-function digital multimeter, different functions have their corresponding maximum and minimum values that can be measured. For example: 41/2-digit multimeter, the test range of DC voltage range is 0.01mV～1000V.
5. Measurement rate
The measurement rate, which is expressed in terms of "times/s," is the frequency at which an electric current is measured by a digital multimeter. It primarily depends on the A/D converter's conversion rate.
The measurement period is used by some portable digital multimeters to indicate measurement speed. The measurement cycle is the length of time needed to perform a measurement operation.
The measurement rate and the accuracy index are at odds with one another. It is challenging to strike a balance between the two because typically the higher the accuracy, the lower the measurement rate. You can set different display digits or the measurement speed conversion switch on the same multimeter to resolve this contradiction:
Add a fast measurement file, which is used for the A/D converter with a fast measurement rate; the measurement rate can be greatly increased by reducing the number of display digits. This method is currently widely used and can meet the needs of different users for the measurement rate.
6. Input impedance、
When measuring voltage, the instrument should have a very high input impedance, so that the current drawn from the circuit under test is very small during the measurement process, which will not affect the working status of the circuit under test or the signal source, and can reduce measurement errors.
For example: The input resistance of the DC voltage range of a 31/2-digit handheld digital multimeter is generally 10μΩ. The AC voltage file is affected by the input capacitance, and its input impedance is generally lower than that of the DC voltage file.
When measuring current, the instrument should have a very low input impedance, so that the influence of the instrument on the circuit under test can be reduced as much as possible after being connected to the circuit under test. Burn out the meter, please pay attention when using it.
