How to Select a Digital Multimeter 1?

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How to Select a Digital Multimeter 1?

A user needs to take into consideration the following aspects as he/she is selecting a digital multimeter: function, accuracy, safety, and convenience to use.

  1. Accuracy

There is no such a multimeter that will be never in error in the world. Multimeters of distinct brands and types will differ sharply in accuracy. On the part of users, they may make a synthetic judgment about the accuracy of a multimeter in terms of digit display, resolution, precision, and true virtual value, etc.

Digit display means the digits of a measuring result that a multimeter will be able to display. For example, a three-digit multimeter will be able to present a full-digital reading that comprises three numbers from zero to nine, plus a digit and a decimal point, that is, the reading of the multimeter is in the range of 0.001-1999. A 3.5-digit multimeter will display a full-digital reading that consists of three numbers from 0 to 9, plus either 1 or 0 half digit; that is, the reading of such multimeter is in the range of 0.001-1999. Apart from the whole digit and half digit, the notion “count” has been introduced nowadays, i.e. maximum display of reading. For instance, the reading of a 3.5-digit multimeter is 1999 counts and 4-digit multimeter 9999 counts. Besides, 4000 counts, 6000 counts, and 20000 counts multimeters are also common in the market.

Resolution is the minimum parametric variation that a multimeter can detect. For example, when a multimeter with 0.01V resolution measures a voltage whose actual value is 3.456789V, it will only display 3.45, while the multimeter whose resolution is 0.001V will display 3.456, which adds one more vector to the former.

To take Zotek’s ZT98 (1999 counts) and ZT101 (6000 counts) for example, let’s assume that a multimeter is errorless when a user measures a 1.999V voltage, the reading of ZT98 is 1.999V and the resolution is 0.001V, the same is true for the ZT101 multimeter. There is no error in the actual values of the both multimeters, but when the user measures a 2.001V voltage, the reading of ZT98 will miss its first digit 2; thus, the decimal point will move towards the right; the reading will be 02.00V and the resolution will reduce to 0.01V. However, ZT101 will be still able to display 2.001V and its resolution will be 0.001V as well. The error occurs in the multimeter with fewer counts. Consequently, on condition that precision is equivalent, the more counts and the higher resolution a multimeter has, the more digits than the multimeter will display in its reading and the less error it will cause.