Measurement with analog instrument

Example: What is total uncertainty of measurement result obtained by one measurement with analog voltmeter of accuracy class 1,5 on range 150 V ( = 150 divisions), if pointer was exactly on one third of range ( = 50,0 div.)?

Limits of error of measured quantity are:

and limits of error expressed in measurement units are:

Total uncertainty of measured voltage, expressed in percentage, is

or expressed in measurement units:

Analog measuring instruments are instruments by which the measured quantity is determined by position of pointer on the scale. Analog measuring instruments are divided into accuracy classes: 0,05 - 0,1 - 0,2 - 0,3 0,5 - 1 - 1,5 - 2 2,5 3 - 5. Stated numbers are indexes of accuracy class, and they inform us about percentage limits of error. Percentages are usually given in relation to full scale (maximum value of measurement range), and in very rare cases is related to reading.

If we want to express measurement uncertainty in percentage, first we need to transform limits of error expressed as percentage of full scale, G%D, into percentage of reading:

where G%M M is limit of relative error expressed in percentage of reading, is the full scale expressed in scale divisions (or measurement units) and a is reading expressed in divisions (or measurement units).

If we want to express measurement uncertainty in absolute value (measurement units), then we need first to transform limits of error expressed in percentage into limits of absolute error:

where Ga is limit of absolute error expressed in measurement units, G%M is limit of relative error expressed in percentage, G%D is limit of error expressed in percentage of full scale, is full scale in measurement units and is the reading also expressed in measurement units.

:: EXAMPLES ::

Proper expression of measurement result on M level.
Proper expression of measurement result on L level.
Correct expression of measurement result.
Absolute, relative and percentage errors.
Determination of resistance measurement uncertainty.
Expression of measurement result represented with expanded uncertainty.
Corrected measurement result.
Standard deviation of arithmetic mean.
Measurement with digital instrument.
Estimation of uncertainty from worst-case limits of error
Combined measurement uncertainty
U-I method for measuring small resistance
Measuring resistance with digital ohmmeter
Standard deviation of weighted average