How is the accuracy of digital displays defined?
The technical specifications indicate the absolute and relative accuracy. In addition, it is also important how many digits (counts) the digital display has.
If you look at a measuring device with a digital display, two different measurement uncertainties have to be expected.
The accuracy indicates the maximum possible deviation. But of course, the deviation could also be smaller.
The following example will show the how to evalute the absolute deviation, the relative deviation and the number of the the displayed digits (counts).
Example: Digital Multimeter Fluke 87V
Accuracy according to technical specifications:
Our example should refers to a measurement with a displayed voltage of 230.0 V at 50 Hz.
Thus, according to the table, an accuracy of ± (0.7 % + 2) would be expected
| This is the relative error (in %) and refers to the displayed measurement result | This is the absolute error and refers to the last place of the display |
This means that the relative error (0.7% of 230.0 V) equals to 1.61 V.
The absolute error is 2 digits (as the least significant digit has a value of 0.1 V), this equals to 0.2 V
In our example, a total measurement tolerance of 1.61 V + 0.2 V = 1.81 V has to be expected.
So at a displayed value of 230.0 V, the "true" value can be between 228.19 V and 231.81 V.