Q1. TABLE A gives the response of a particular temperature sensing element over the temperature range of 0 ºC to 250 ºC.
a) Determine the equation of the ideal straight line for the sensing element over the temperature range of 0 ºC to 250 ºC.
b) Copy the table and complete rows 3 and 4.
[R(ISL) is the ideal straight line value of resistance and N(T) is the non- linearity of the element.]
c) Draw a graph of the non-linearity N(T) against temperature.
d) Determine the maximum non-linearity of the sensor as a percentage of output span.
Table A
|
Temperature ºC
|
0
|
50
|
100
|
150
|
200
|
250
|
|
Resistance Ω
|
120
|
178
|
201
|
249
|
303
|
364
|
|
R (ISL) Ω
|
|
|
|
|
|
|
|
N(T) Ω
|
|
|
|
|
|
|
Q2. a) Determine the nature of the flow [turbulent or laminar] for liquid flowing at 1 ms-1 in a 20 mm diameter pipe if the liquid is:
i) water [ Ρ = 1000 kg/m3 , μ = 1x10-3 Ns/m2]
ii) crude oil [ Ρ = 860 kg/m3 , μ = 10x10-3 Ns/m2]
b) For many liquids viscosity is strongly dependent on temperature. Use the table below to estimate the required maximum temperature of crude oil to flow at a rate of 4 kg s-1 through a 0.3 metre diameter pipe whilst maintaining a laminar flow.
|
Crude Oil (sg = 0.855)
|
Temperature °C
|
|
0
|
20
|
50
|
100
|
200
|
|
Viscosity ( x 10-3 Nsm-2 )
|
16
|
7.5
|
4
|
2.5
|
1.5
|
Q3. Select, giving reasons, the most suitable choice of temperature sensor for use in the following scenarios:
a) Measuring the temperature of a printed circuit board in a computer.
b) Measuring the temperature in a glass melting furnace that operates at temperatures of up to 1600 °C.
c) Reliable measurement of the temperature in a pharmaceutical process over the range 0 to 300 °C and within ±0.5 °C.
d) Measuring the water temperature in a dishwasher.
e) Measuring the rate of change of temperature at a particular spot on the cylinder head on an internal combustion engine.
f) Measuring temperature of the behaviour of metals at very low temperatures (123 to 70 K) in a cryogenics laboratory.
Q4. There is a requirement to design a system to sense the presence of glass bottles leaving an automatic washer on a production line conveyor belt. The production line is for food products and the environment is clean and maintained at a temperature of 15°C.
The system must meet the following criteria:
- The switching distance will lie between 5 and 20 mm.
- The output from the sensor is to be of binary form, i.e. logical 1 when the part is present and logical 0 when no part is present.
- It is necessary to ensure that a change of sensor state occurs closer to the sensor when a bottle approaches than when it moves away.
- Bottles will pass the sensor at the rate of 10 every second.
- There is no requirement for protection from contact with objects but it must be proof against water drips.
Recommend a suitable sensor and justify your recommendation. Sketch a diagram that shows the functional blocks within the sensor and explain each function.
Give the necessary Protection Code. [You may refer to the tables in Lesson ICP - 1 - 8.}
Q5. The full range input of a12-bit, successive-approximation type ADC is 1 volt. Determine:
a) the maximum input change required to give a one bit change in output of the ADC
b) The number of approximations made to complete the conversion of an input signal of 0.8125 V and the final binary result of the conversion process.
Q6. A hydraulic jack has a load piston diameter of 150 mm, and a plunger diameter of 25 mm.
a) Ignoring losses, calculate the force needed on the plunger to raise a load of 2500 kg.
b) Calculate how many strokes of the plunger will be required to raise the load 180 mm, if each stroke of the plunger is 100 mm long.
Q7. Figure 1(a) gives a block diagram showing an input to a programmable logic controller (PLC).
In this example a mains [230V] push button is connected to the input.
A requirement is to have electrical isolation between the mains supply and the delicate logic of the PLC. Figure 1(b) shows the circuitry on the ‘mains' side of the input.
Describe a way of achieving the coupling between the push button and the PLC and briefly explain the purpose of the ‘mains circuitry'.
Q8. An instrumentation measuring system uses a differential amplifier having a CMRR of 120 dB and differential gain of 105. The maximum differential input signal is 60 µV. If the amplified noise voltage is specified to be not more than 1% of the maximum output voltage, calculate the maximum common mode voltage that can be present in the input to the amplifier.