A handheld infrared thermometer has a range of -50 °C to 375 °C. The thermometer

Question

A handheld infrared thermometer has a range of -50 °C to 375 °C. The thermometer has a voltage output of 0-1 volt corresponding to the temperature range that can measured using a data acquisition (DAQ) system. If a DAQ system with a 16-bit A/D converter, with an A/D converter range of ±10 V, and with a gain of 5 is used to record the thermometer output, what is the resolution of the thermometer measurements in °C? What is the sensed voltage range of the DAQ system? Is the “gain of 5” the optimum gain for this signal? Why or why not?

Explanation / Answer

Let's first calculate the Resolution of A/D converter

Resolution = Range / 2n              ( n = number of bits of converter )

Resolution =+/- 10 V / 216 = +/- 10 V / 65536 =+/- 0.152 mV

Now handheld Thermometer gives out put of 0 - 1 Volt for -50 to 375 Deg.C.

Gain of 5 is used before it is converted to digital by ADC

input to ADC is in range of 0 - 5 Volts.

375 Deg.C corresponds to 5 V therfore 0.152 mV corresponds to

Resolution in Deg.C = 375*0.152 mV / 5 V = 0.375*0.152 / 5 = 0.0114

Resolution in Deg.C = 0.0114 Deg.C                 .......1

This is the required resolution of thermometer in Deg.C

Now handheld Thermometer gives out put of 0 - 1 Volt for -50 to 375 Deg.C.

Gain of 5 is used before it is converted to digital by ADC

Sensed voltage range to DAQ system is in range of 0 - 5 Volts.                    ........2

Since A/D conveter has range of +/-10 V and input is just 5 Volts full range of ADC is not used.

Hence gain of 5 is not optimum.Gian of 10 should have been used.      ...........3

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