Your boss asks you to classify some of the components in a temperature measureme

Question

Your boss asks you to classify some of the components in a temperature measurement system. The system consists of a thermocouple and an analog-digital conversion (ADC) device. The thermocouple has a linear response from 0 to 70°C. Over this range, its minimum output voltage is 0 V and its maximum output voltage is 3.649 mV. The ADC device has 8 bits and two possible input ranges: ±5 mV and ±5 V. You can assume that the ADC rounding process operates in the same manner as we discussed in class.

- Determinetheresolutionvoltageanditsrelateduncertaintyofthe ADC for both input ranges.

- Determinethesensitivityofthethermocouple.

- You set a water bath to a 57°C temperature and place the

thermocouple in the bath.

* What do you expect the thermocouple voltage to read?

* Based off both ADC input ranges, what do you expect the ADC output voltage to read?

* How can you explain the difference in values?

* Which input range is optimal for this measurement scenario?

- Based on the previous step and the lower ADC input range: If you didn't know the bath temperature and only knew the ADC voltage,

what temperature would you say the bath is set to?

Explanation / Answer

1) Resolution and uncertainty of both ADC ranges

a) Resolution (for +/- 5 mV range) = 5 mV / 2n where n = number of bits of ADC

Resolution = 5 mV / 28 = 5 mV / 256 = 0.0195 mV    ..................1

uncertainty (for +/- 5 mV range) = +/- 0.5*resolution = +/- 0.5*0.0195 mV = 0.00975 mV       ..........2

b) Resolution (for +/- 5 V range) = 5 V / 2n where n = number of bits of ADC

Resolution = 5 mV / 28 = 5 V / 256 = 0.0195 V = 19.5 mV    ..................3

uncertainty (for +/- 5 mV range) = +/- 0.5*resolution = +/- 0.5*19.5 mV = 9.75 mV       ..........4

2)Thermocouple sensitivity = ( Maximum output voltage - Minimum Output voltage) / (Maximum Temperature - Minimum Temperature)

Thermocouple sensitivity = (3.649mv - 0 ) / (70 - 0) = 0.0521 mV / Deg.C           ............5

This is the required Thermocouple sensitivity

3) Water bath temperature is given as 57 deg.C

Hence voltage read by Thermocouple = Sensitivity*57 = 0.0521*57 mV = 2.9697 mV    ........6

4)We need to use ADC with a range of +/- 5 mV range as ADC with +/- 5 V range can not do measurement as it's resolution is higher than output voltage.

ADC will measure voltage as 2.9695 mV                    ......................7

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