Example Sheet 2
1. LongQuestionExample
(a) Explain the Seebeck effect and how it is used in thermocouple design. [8 marks]
(b) Sketch a graph for how the EMF of a thermocouple changes with temperature, you should add labels and explain the neutral temperature, the inversion temperature and explain how the sensitivity can be obtained from this graph.
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(c) Using the table on slide 5 of lecture 4b work out the sensitivity of a thermocouple which is made from copper and constantan.
(d) What is the measured voltage if the hot junction is at 50 degrees C and the cold junction is at room temperature?
(e) Suggest a circuit and the required gain to match this to a digitisation circuit operating over +/-1 Volts with a depth of12 bits if the temperature is to be measured to 0.25K accuracy
(f) What is the max temp that can be measured assuming the cold junction is at 0 degrees C
2. What is the frequency of a light source where, λ = 550 nm? How much energy does a single photon contain?
3. Whatisthephotonflux(photonspersecond)foralaserpointerwiththefollowing specifications? λ = 800 nm, P = 100 mW
4. A photodiode has a dark leakage current of 10 nA, a shunt resistance of 750 MΩ and a responsivity of 0.6 AW-1 at the wavelength we are using, if the bandwidth B is 1 Hz: standard room temperature (25 degrees Celsius):
calculate: shot noise current, Johnson noise current, total noise current, NEP.
5. A signal has the form: 𝑠(𝑡) = 𝑎 + 𝑏 sin(2𝜋𝑓𝑡) volts Where a = 2.5V, b = 1mV and f=1MHz.
If the ADC being used to digitise this signal has an input range of 0-5V, and we require at least 10 levels to capture the full scale of the signal. How many bits must the ADC have and what would be a suitable sampling frequency.
EEEE3089 Sensing system and signal processing 2020-2021
6. What is the quantisation noise introduced by a 12 bit ADC? And what is the max SNR that can be obtained for this device assuming it operates over a +/-1V range?
7. Describe how signals and signal processing are used in biomedical applications. Explain the impact this has to the wider world giving examples of specific applications. Discuss the types of techniques and approaches used.
8. Explain how quantisation noise arises during analogue to digital conversion and how the size of the noise is related to the number of bits used.
EEEE3089 Sensing system and signal processing 2020-2021
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