Introduction à Technique Spécifications de Numérique Multimètres
1. Number of display digits and display characteristics
Le affichage chiffres de a numérique multimètre sont généralement 31/2 à 81/2 chiffres. There are two principles for determining the display digits of a digital instrument:
Un est que le nombre de chiffres que can afficher tous nombres de 0 à 9 is an entier;
The second is that the numerical value of the fractional digit is represented by the high digit in the * large display value as the numerator. At full scale, the value is 2000, indicating that the instrument has 3 integer digits. The numerator of the decimal digit is 1, and the denominateur is 2, so it is called 31/2 digits, pronounced as % 22trois et a demi chiffres". Le haut chiffre can only display 0 ou 1 (0 is usually not display).
The high bit * of a 32/3 digit (prononcé as "three and two-thirds digits") digital multimeter can only display 0-2} digits, so the * large display value is ± 2999. In the same situation, it is 50 percent higher than the limit of a 31/2 digit digital multimeter, especially valuable for measuring 380V AC voltage.
For example, when measuring power grid voltage with a digital multimeter, the highest digit of a regular 31/2 digit digital multimeter can only be 0 or 1. To measure 220V or 380V power grid voltage, only three digits can be display, and the resolution of this range is only 1V.
In contrast, using a 33/4-bit digital multimeter to measure grid voltage, the high bit can display 0-3, which can be display in four digits with a resolution of 0.1V, which is the same as a 41/2-bit digital multimeter.
Universel numérique multimètres généralement appartenance à portable multimètres avec a 31/2 chiffre affichage. 41/2, 51/2 chiffre (ci-dessous 6 chiffres) numérique multimètres are divisé en deux types: portable et bureau. Most desktop digital multimeters with 61/2 digits or more belong to the category.
2. Précision
La précision de un numérique multimètre est la combinaison de systématique et aléatoire erreurs dans mesure résultats. Il représente le degré de cohérence entre la valeur mesurée et la vraie valeur, et aussi reflète la magnitude de mesure erreur. Généralement parlant, le plus élevé la précision, le plus petit le mesure erreur, et vice versa.
There are three ways to express accuracy, as follows:
Précision=± (a percent RDG plus b percent FS) (2.2.1)
Précision=± (a percent RDG plus n words) (2.2.2)
Précision=± (a percent RDG plus b percent FS plus n words) (2.2.3)
In equation (2.2.1), RDG représente la lecture valeur (i.e. display value), FS représente the full scale value, the previous item in parenthèses represents the complete error of the A/D converter and functional converter (such as voltage divider, splitter, true RMS converter), and the latter item is the error caused by digital processing.
In equation (2.2.2), n is the change in quantization error reflected in the last digit. If the error of n words is converted en a percentage of full scale, it devient equation (2.2.1). Equation (2.2.3) is assez unique, and some manufacturers use this expression. One of the last two represents errors introduit by other environments or functions.
The accuracy of a digital multimeter is much better than that of an analog pointer multimeter. Taking the accuracy index of the basic range for measuring DC voltage as an example, it can reach ± {{0}}.5 percent for 3 and a half bits, and 0.03 percent for 4 and a half bits.
For example, OI857 and OI859CF multimeters. The accuracy of a multimeter is a very important indicator, which reflects the quality and process capability of the multimeter. A multimeter with poor accuracy is difficult to express the true value, which can easily lead to misjudgment in measurement.
3. Résolution (résolution)
The voltage value correspondant to the last one word on the low voltage range of a digital multimeter is called resolution, which reflects the sensitivity of the instrument.
La résolution de numérique instruments augmente avec le nombre de affiché chiffres. Le haut résolution indicateurs que a numérique multimètre avec différents chiffres can atteindre sont différents, tel as a 31/2 digit multimeter with 100 μ V.
Le résolution index de a numérique multimètre can also be display using resolution. Resolution renvoie à le pourcentage de * petit chiffres (excluant zéro) et * grand chiffres that the instrument can display.
For example, a typical 31/2 digit multimeter can display a resolution of 1/1999 ≈ 0.05 percent , with a small number of 1 and a large number of 1999.
It should be pointd out that resolution and accuracy belong to two different_concepts. The former characterise the "sensitivity" of the instrument, that is, the ability to "recognize" small voltages; The latter reflects the "accuracy" of the measurement, that is, the degree of consistency between the measurement results and the true value.
From a measurement perspective, resolution is the "virtual" indicator (independent of measurement error), while accuracy is the "real" indicator (which determines the size of measurement error). Therefore, augmentant the number of display digits arbitrairement to improve the resolution of the instrument is not faisable.
4. Mesure Plage
In a multifunctional digital multimeter, different functions have corresponding maximum and minimum values that can be measured. For example, with a 41/2 digit multimeter, the testing range for DC voltage range is 0.01mV to 1000V.
5. Mesure taux
Le nombre de fois a numérique multimètre mesure la quantité de électricité être mesuré par seconde est appelé le mesure taux, et son unité est "times/s. It principalement dépend de le taux conversion taux du A/D convertisseur.
Some handheld digital multimeters use measurement cycles to indicate the speed of measurement. The time required to complete a measurement process is called the measurement cycle.
There is a contradiction entre mesure taux et précision indicateurs, habituellement le supérieur le précision, le inférieur le mesure taux, et it est difficile à équilibre le deux. à résoudre ceci contradiction, différent affichage chiffres ou mesure vitesse conversion commutateurs can be set on the same multimeter:
Add a fast measurement range for A/D converters with faster measurement rates; By reducing the number of display digits, the measurement rate can be significative increased. This method is currently commonly used and can meet the needs of different users for measurement rate.
6. Entrée impédance
Lorsque mesure tension, le instrument devrait avoir a haut entrée impédance, so que le courant dessiné de le circuit mesuré pendant le processus mesure est minimal et ne pas affect le état de le circuit mesuré ou signal source, qui peut réduire mesure erreurs.
For example, the input resistance of a 31/2-bit handheld digital multimeter in the DC voltage range is general 10 μ Ω. The AC voltage range is influenced by the input capacitance, and its input impedance is general lower than the DC voltage range.
Quand mesure courant, le instrument devrait avoir a très faible entrée impédance, qui peut minimiser le impact de l’instrument sur le circuit mesuré as much as possible after being connected to the measured circuit. Cependant, when using the current range of a multimeter, due to the small input impedance, it is easy to burn the instrument. Please be careful when using it.
