Chapter VII Description of Experimental Setups
7.3 Description of experimental setups
7.3.1 Setup of experiments 1: Basic data acquisition and logging experiments.
Figure 87 shows a simplified diagram for the setup of experiment 1. In the figure, the temperature sensor LM35DT placed on the main board is read through the analogue multiplexer on the ADC board. The relevant channel is selected by sending a channel select word through the address bus (local 2 = LB2).
Figure 87 - Simplified diagram of the setup for the ambient temperature acquisition and logging experiment
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The AD conversion is performed using the internal MCU’s ADC. The data are read and temporarily stored in a buffer in MCU’s RAM. The data are later sent to the PC via serial port RS232. The data logging is performed by the data logging MCUs software component and the DatalogWinlink PC side program, all of which were described in the previous chapter VI. The results are presented in the next chapter.
Sample tables of the recorded data can be found in the appendix C.
7.3.2 Setup of experiments 2: Thermocouple data acquisition and logging experiments.
The figure above shows the basic setup for this experiment. In the figure, a K type temperature measuring junction is placed in air (of the lab room). The thermocouple is interfaced to the thermocouple-to-digital converter through a differential channels analogue multiplexer (DG407) placed on the TDC board. The relevant channel is selected by sending a channel select word through the address bus (local 2 = LB2).
The TD conversion is performed by the MAX6675 TDC. The data are read via the SPI bus and temporarily stored in a buffer in MCU’s RAM. The data are afterwards sent to the PC via serial port RS232. The data logging is performed by the data logging MCUs software component and the DatalogWinlink PC side program, all of them described in the previous chapter VI. Sample tables of the recorded data can be found in the appendix C.
Figure 88- Simplified diagram showing the setup for the thermocoulple acquisition and logging experiments.
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7.3.3 Setup of experiment 3: The “ice to boiling” experiment.
7.3.3.1 Experimental setup description
Figure 89 above shows the basic setup for this experiment. The behaviour of water temperature when it is heated from ice (solid) state up to boiling (vapour/gas) is known. If the water is pure and the experiment is done at sea level under normal pressure, then, the melting and boiling points are known to be 0 and 100 degrees Celsius, respectively. Assuming the above conditions, the temperature behaviour is as follows:
• The water in ice state is heated from an initial temperature that is below zero (i.e., ice melting has not started);
• The water (ice) temperature increases until it reaches 00C, where the ice starts melting (phase change from solid to liquid). Liquid water and ice coexist during phase change;
• The temperature remains constant and equal to zero while melting is taking place until all the ice is completely melt. The energy received from the heating is spent on the phase change process;
• Once melting is finished the water temperature starts increasing up to 1000C.
At this point, water is boiling and a phase change of water from liquid to gas (vapour) is taking place;
• The boiling water temperature will remain constant and equal to 1000C until all the water is evaporated.
Figure 89 - Simplified diagram showing the setup for the "ice to boiling experiment"
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This can be used to roughly evaluate the reliability of and calibrate the thermocouple temperature reading scheme, assuming that the conditions are respected.
The lab (UKZN, physics) is at approximately 200m above the sea level. The vapour pressure of water at 200m above sea level is about 99.350C [for calculation see (Nave, 2005)].
Procedure:
A pot (beaker) with ice at a temperature below zero is heated continually. The pot temperature increases until the ice starts melting;
A K type thermocouple measuring junction is immersed into the melting ice. The thermocouple is interfaced to the thermocouple-to-digital converter (MAX6675) through a differential channels analogue multiplexer (DG407) both placed on the TDC board. The relevant channel is selected by sending a channel select word through the address bus (local bus 2 = LB2).
TD conversion is performed by the MAX6675 TDC and data are read by the MCU via the SPI bus and temporarily stored in a buffer in RAM. The data are afterwards sent to the PC via serial port RS232. The data logging is performed by the data logging MCUs software component and the DatalogWinlink PC side program, all of them described in the previous chapter VI. Soon after boiling starts taking place the thermocouple is removed from the pot and placed in ambient air. Sample tables of the recorded data can be found in the appendix C.
Below is a figure showing the expected behaviour of water temperature from ice melting to water boiling conditions.
7.3.3.2 Expected results
Figure 90 - Expected thermocouple temperature behavior for the "ice to boiling experiment"
7.3.4 Setup of experiment 4: “Basic Tracker control functionality experiments”.
The figure above shows the basic setup for this experiment. In the figure, the tracker controller drives the motion of the dish (according to the control laws and supervisory controller inputs discussed earlier, see section 6.5.5.1). A single turn linear potentiometer is attached to each of the tracking axes. This is connected to act as an angle to voltage converter (AVC). In this way, the dish angular position in both axes is recorded by the AVC potentiometers. The AVCs are read through the analogue multiplexer on the ADC board. The relevant channels are selected by sending a channel select word through the address bus (local bus 2 = LB2).
The AD conversion is performed by the internal MCU’s ADC. The data are read and temporarily stored in a buffer in MCU’s RAM and soon afterwards sent to the PC via serial port RS232. Sample tables of the recorded data can be found in the appendix C.
Figure 91 - Simplified diagram showing the setup for the "basic tracker control functionalityexperiments"
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7.3.5 Setup of experiments 5: Integrated tracker control with temperature acquisition and logging experiment.
Figure 92 shows the basic setup for this experiment (which is the same as the previous one, except that the TDC board and the SPI interface are now part of the experiment). In the figure, as with the previous setup, the tracker controller drives the motion of the dish. While some of the 2 axes rotates, it drives a rigidly fitted AVC potentiometer, as a means of giving back the dish angular position of the relevant axis. The AVCs are read through the analogue multiplexer on the ADC board. The relevant channels are selected by sending a channel select word through the address bus. The AD conversion is performed by the MCU’s ADC.
In turn, K type thermocouples measuring junctions are placed on various points of interest (Receiver’s inlet and outlet, Receiver’s outer surface, TES inlet and outlet, some TES inside profile levels an ambient/air). The thermocouples are interfaced to the MAX6675 TDC through the DG407 analogue multiplexer. TD conversion takes place and data is read by the MCU via the SPI bus and temporarily stored in a buffer in RAM. Both the ADC and the TDC data are sent to the PC via the RS232 serial interface.
Figure 92 - Simplified diagram for the integrated tracker control and temperature acquisition experiment.
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