Re: In what situations would I want to use the Interval Package?

[Oliver Heimlich]

On 22.12.2017 17:07, shall689 wrote:
> In what situations would I want to use the Interval Package?
> 
> Would it be useful in determine the effect of ADC Quantization error?
> 
> Thanks
> Stephen

Hi Stephen,

the interval package can be used to model all kinds of (worst case)
errors.  For example, when I build a temperature sensor with my Arduino
One, I can use the internal ADC to measure the output of a TMP36
temperature sensor.

According to the specs, the ADC has a 10-bit resolution with an abolute
error of +-2 LSB.  If the ADC returns a value of x = 153, we can compute
the corresponding voltage and temperatur (in °C) with error bounds for
the ADC:

>> x = 153;
>> pkg load interval
>> adc_err = infsup ("[-2, 2]");
>> voltage = (x + adc_err) / 1024 * 5
voltage ⊂ [0.7373, 0.75684]
>> temperature = (voltage - .5) * 100
temperature ⊂ [23.73, 25.684]

As you can see, the ADC quantization error already introduces an error
of 2°C.  Now, we can add the error of the temperature sensor according
to its specs (around 25°C there is a max error of +- 2°C).

>> temperature + infsup ("[-2, 2]")
ans ⊂ [21.73, 27.684]

As you can see, such a temperature sensor is not very accurate without
calibration.

Best
Oliver

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