DMM ACCURACY – Oscar Zavaleta Weighing Industry

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Unexplained Specifications

The post begins with terminology meaning and culminates comparing them. It explains the source and reason for percent reading and percent range. Exercise caution beyond operational limits and take into account temperature.

DIGITS
The quantity of number the instrument claims to display. Typical values are 3 ½, 4 ¾, 5 ½, 6½, 7 ½ & 8 ½.

RESOLUTION
The number of counts the instrument can display in n division increments. A 50,000 counts does not mean it has a 50,000 counts accuracy. Resolution and accuracy are not mutually dependent & listed separate on specs. Meters can have expanded and internal resolution.

RANGE
The upper and lower limit of measurement. Used to prevent damage to the instrument. For instance 0.5 V DC to 5 V DC

ACCURACY
The range can significantly impact measurement accuracy. A low resolution DMM may have higher accuracy than a high resolution one. Low accuracy does not mean instrument is outside specifications. It simply means, it is not as exact as the standard. Do not assume a 50 k counts has higher accuracy than a 5 k one.

PERCENT READING
Originates as a result of components’ tolerances, nonlinearities, … Different ranges may share similar basic accuracy specs.

PERCENT RANGE
Source of this uncertainty arise from noise, rounding, …. Different ranges may share similar percent deviation.

TEMPERATURE COEFFICIENT
The factor by which reading must be added to the reading when measuring outside the ideal temperature range.

OPERATIONAL HUMIDITY
The limit at which the instrument must be used. Different relative humidity levels per temperature range. Ommission does not mean it has no effect.

OPERATIONAL ALTITUDE
Electronics in high elevation places may arc due to natural phenomena. Avoid use if operating above this distance from sea level. Omission does not equate to unlimited height.

COMPARISON

Resolution refers to counts the instrument can display. Accuracy refers to how exact the measurement is.
Uncertainty: The range in which the exact value can be.
Repeatability: Refers to how close similar measurements are.
Error: Deviation from the exact value.

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