Agilent Technologies U1270 Series Especificaciones descargar pdf (Pagina 3)

Things to Consider When Selecting a Multimeter

Resolution, digit, and accuracy

Resolution is defined as the smallest change in an input signal that produces a

change in the output signal. Resolution of a DMM is expressed in the number

of digits the unit can display. For example, a 4½ DMM has four full digits that

display values from 0 to 9, and the fractional digit, which is the most significant

digit in the display. The fractional digit represents the highest level the most

significant digit can display. In this example it is either a 0 or 1. Such a meter

can also show positive or negative values from 0 to 19,999.

Sometimes resolution specified as the number of digits a DMM can display

causes confusion, so manufacturers started specifying resolution in terms of

“count”. The count of a DMM refers to how large a number it can display before

it has to change measurement ranges, and how many digits it shows in total.

This effects how precise a measurement the DMM can display. For example, a

4½ DMM can also be specified as a 19,999 display count or 20,000 display count

multimeter.

Multimeter digit Display range Count

3½ ±1,999 2,000

4½ ±19,999 20,000

3¾ ±3,999 4,000

The accuracy of the DMM is different from the display resolution. The accuracy

is the maximum allowable limit of error in the readings. All the DMM manufac-

turers express the accuracy specifications as ±(% of reading + number of least

significant digit (LSD)). The reading is the true value of the signal that the DMM

measures. The LSD represents the error due to internal analog digital converter

(ADC) tolerances, offset noise, and rounding errors that vary from function to

function.

If a 4½-digit DMM with a DC voltage accuracy of ±(1% + 2) is measuring a

10.5VDC output, the meter is expected to display a reading of 10.5 V ± 1%, or

10.395 V to 10.605 V. When the LSD count is taken into consideration, the last

digit on the display can vary by ±2 counts. If the meter is set to the 20 V range,

the two count will be 0.002 V. The total accuracy is ±((10.5 x (1/100)) + 0.002) =

±0.107 V. The meter can display a value of 10.5 ± 0.107 V, or a range of 10.393 V

to 10.607 V.

To choose the handheld DMM that is best suited to your requirements, first

consider the following:

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Agilent Technologies U1270 Series Especificaciones Pagina 3