4. A proposed waste-water tank on the Strenuis Ardua is filled by a centrifugal pump, driven by a permanent-magnet DC mo

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4 A Proposed Waste Water Tank On The Strenuis Ardua Is Filled By A Centrifugal Pump Driven By A Permanent Magnet Dc Mo 1 (104.36 KiB) Viewed 16 times

4 A Proposed Waste Water Tank On The Strenuis Ardua Is Filled By A Centrifugal Pump Driven By A Permanent Magnet Dc Mo 2 (58.59 KiB) Viewed 16 times

4. A proposed waste-water tank on the Strenuis Ardua is filled by a centrifugal pump, driven by a permanent-magnet DC motor which is controlled by a sensor. A diagram of the sensor circuit is shown in Figure Q4a. 2 ΚΩ 1 mA Rt V 1 ΚΩ sense Figure Q4a: Sensor circuit As the tank level varies it changes the variable resistor Rt, which can take values in the range 0-1 kn. The diode has a forward- bias voltage drop of 0.7 V. (i) Sketch a graph of Vsense versus Rt over the range of possible values. Label any significant values and/or gradients. (ii) Calculate the power dissipated by R, when its resistance is 100 2. (iii) Calculate the current through the diode when R₁ = 800 . [5 marks] [2 marks] [2 marks]
The signal from the tank is buffered and fed to a microcontroller using the filter circuit shown in Fig. Q4b, where V₁ is the input voltage and V, is the output voltage. L ww Vo "Î R1 R2 Figure Q4b: Filter circuit (iv) State whether this is a low-pass or high-pass filter. (v) Find the gain of the circuit at DC. (vi) Derive the transfer function of the circuit. [1 mark] [2 marks] [5 marks]
The torque needed to drive the pump is proportional to the square of the motor's speed of rotation. The armature resistance of the motor is 0.2 0. Its speed is controlled by a DC chopper circuit, formed from a MOSFET and a diode, connected to a DC supply voltage V = 48 V. (vii) Sketch the circuit diagram of the DC chopper, and the equivalent circuit of the motor. Explain the functions of the MOSFET and diode in the circuit. The MOSFET and diode turn-on voltages are both 0.6 V. In tests, when the duty ration of the MOSFET was 30%, the motor speed was found to be 1000 RPM and the current was 12 A. (viii) Taking the average output voltage of the chopper circuit to be n (Vs - 0.6) V, calculate the torque constant of the motor, and the torque constant of the water pump (the constant k in the relation T = kw²). (ix) What duty ratio would be required to double the pump speed? [3 marks] [3 marks] [5 marks] [Total 25 marks]