Converting readings into measured values

AN2159

18/23

Doc ID 11400 Rev 3

subtask_A: convert

e

subtask_B: convert

e

subtask_C: convert

e

subtask_F:

if not OK

e

else {

e

update

e

e

}

6.2

Other values

The ratio between the register value and the actual voltage, current or frequency value is a

function of the voltage and current sensors sensitivity and of the device internal parameters,

like analog amplification, reference voltage, measurement frequency, calibrator, attenuation

of each stage of decimation filter and power meter constant.

Formulas to convert the readings into meaningful values are reported below.

In any case, since the internal parameters values, here given as constants, are subject to

process drift, and the sensors sensitivity are subject to tolerance, even if these fluctuations

are compensated by the calibrators, the best way to obtain the proper parameters is to

measure known signals and calculate the ratio between register value and actual value. The

device linearity will ensure that the ratio will remain constant.

Figure 7, Figure 8 and Figure 9 below shown the signal processing chains for current and

voltage.

Figure 7.

Voltage signal path