AN3137 datasheet(39/42 Pages) STMICROELECTRONICS

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AN3137

Source code examples

Doc ID 16983 Rev 3

39/42

White noise modulation method:

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external signal should be modulated by white noise or small triangle signal (for

instance, from function waveform generator)

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the second line on LCD shows sub LSB resolution from measured signal - averaged

200 samples

●

to stop the method press the “Key” button

Digital filter method:

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a 50 Hz rejection filter (comb filter) is implemented

●

the first line on LCD shows the difference (maximum-minimum) from raw samples

(buffer is 500 samples)

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the second line on LCD shows the difference (maximum-minimum) from 50 Hz filtered

samples

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50 Hz suppression is seen when a DC signal with 50 Hz added noise is applied

●

to stop the method press the “Key” button

ACD calibration method (linear model):

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a linear ADC curve approximation is implemented: Y = k.X + Q

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samples for calibration are sampled first: more samples means better approximation

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the first line on LCD is editable - a real precise value must be entered (measured by

calibration device)

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the second line on LCD shows sample number, navigation cursor and value measured

by ADC

●

use the joystick for entering real value:

–

left/right = cursor left/right movement

–

up/down = increase/decrease of real value

–

center = enter values pair as valid (sample number increases)

●

change the input signal to different level

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enter real value by joystick

●

continue with another signal level ( > 5 samples, for example)

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to stop entering sampling pairs, press the “Key” button

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an information screen appears:

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the first line on LCD shows standard deviation before calibration

–

the second line on LCD shows standard deviation after linear calibration model

calculation

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next screen appears after 3 seconds:

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measured value with applied linear model (calibrated ADC)

–

you can compare the real calibration value with the value on LCD; it should be

very close

–

to stop the method press the “Key” button and before releasing it press the joystick

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