#### Electrical Measurements

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QUESTION 4 Given is temperature sensor with a sensing range 0°C... 100°C and 2% accuracy full-scale. A temperature reading shows 54°C. Determine the maximum possible real temperature for this reading. Write your answer without the unit.

With the battery in Task 2 fully charged and disconnected, the circuit is re-connected as shown above (the battery now supplying the 190 load with other loads and cable resistance included). Determine using Thevenin analysis, the current through the load, the potential difference across the load and the power dissipated by the load.

Task 4 You have been asked to produce waveforms A and B shown to enable laboratory experiments to be carried out. Unfortunately, you only have dc supplies and three ac sinusoidal voltage supplies available. Describe how these supplies can be utilised to produce an approximation to the waveforms A and B showing formulae and calculations used (assuming 100V and 50Hz for the fundamental waveform). Using your calculations, construct the circuit below in Multisim (or something similar) and connect a virtual oscilloscope across the resistor. You must include a clear screen print of the two circuits along with the simulated waveforms. Discuss your findings and suggestions for improvements.

Task 5 (1) Scenario A company manufacturing extra low voltage fluorescent fittings is looking at improving the adaptability and efficiency of their product. The circuit shown below is for a typical ELV fluorescent lamp fitting, which operates at 24V 50Hz. Assuming the fluorescent tube has an operating resistance of 300 and an ideal transformer, determine: a. the current supplied by the source b. the impedance seen at the supply (HV side) c. the power dissipated by the tube d. the operating power factor of the fitting (ii) If the capacitor is now removed from the above circuit and is placed in parallel with the secondary of the transformer, recalculate a to d in question (i). Using a scale phasor diagram prove your answer to part (ii) d. and evaluate each technique for determining circuit power factor. (iii) Write a brief report of your findings in parts (i) to (ii) which will be submitted to the company director (200 words). (iv) After reading the report in part (iv) the director asks why the fitting cannot simply be connected to a dc supply and the choke replaced by a resistor. In a written reply to this, explain the operating principle of the transformer in the above circuit and the operating principle and purpose of the choke when used in conjunction with a starter switch in a fluorescent switch start circuit, with particular reference to electro-magnetic induction and induced emfs.

1. Does the transformer draw current from the source, even there is no-load connected to it? If yes, explain why?

2. Discuss how to determine the magnetizing and working component of the no-load current and draw the phasor diagram to represent these quantities.

4. A 40 kVA, 2000/200 V single-phase transformer has a core loss of 600W at rated voltage and a copper loss of 500W at rated current. Calculate the efficiency at i) full load with unity power factor, half load with 0.85 power factor lagging.

Figure Q2.1 represents the true value of a noisy signal which is to be displayed on an oscilloscope, in order to estimate the amplitude and period of the underlying sawtooth waveform. a. Suggest appropriate vertical axis and timebase settings for the oscilloscope. b. How should the oscilloscope be triggered? Your answer should indicate where on the waveform you plan to trigger (and why!) and how the oscilloscope can be configured to achieve this. c. Two oscilloscopes are available, a 500 MHz 3 GSPS model and a 100 MHz 500 MSPS model. i. Explain what these specifications mean. ii. How will the displayed waveform differ between the two scopes? iii. Which scope is better suited to the measurement described?

A transformer has two coils wound on a common core having self-inductances, L₁ = 1H, L2 = 2 H, and a mutual inductance, M = 0.5 H. The currents are i₁ = cos (120 лt) A and i₂ = 0.5 cos (120 лt) A. Assuming a positive mutual inductance for the set of coils, use Faraday's Law of induction to determine v₁ and v₂. Show all of the details.

a. Explain why input impedance is an important property of a voltmeter (and other circuits used for voltage measurement). b. A force sensor has an output of 1 V kN-¹ and an output impedance of 1 kΩ, as shown in Figure Q1.1(a). A force of 2 kN is applied to the sensor. Calculate the measured voltage, equivalent force and insertion error when the sensor's output is measured using: i. An ideal voltmeter (Figure Q1.1(b)) ii. A DMM of input impedance 40 MΩ (Figure Q1.1(d))