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Week 13: 7th November to 13th NovemberEdit

This week I ran a few additional experiments, the results of which are to be presented in the CA2 report.

Experiment 1: Hall effect sensor reading versus vertical distance at 10 V power and 17 V

Expt 1 results

Figure 1: Table of Results of Sensor output at various distances above electromagnet at 10 V and 17 V power










The experiment was conducted with a Hall effect sensor and an electromagnet, which generates an average flux density on the surface from 450 to 1950 Gauss for the range of 6V to 24V with 1.9A to 7.5A of electric current. The sensor is positioned on the vertical axis above the electromagnet. The value of the sensor output voltage taken is the men value in one second.

This experiment consists of two parts. The first part entails powering the electromagnet with a constant voltage of 10 V while in the second part the electromagnet is powered using a constant voltage of 17 V. The output voltage from the sensor is recorded at various distances above the electromagnet when it is powered at 10 V and 17 V. The aim of this experiment is to investigate the effectiveness of increasing the power supplied to the electromagnet in increasing the sensitivity of the hall effect sensor in detecting a voltage drop.

It is observed that while the effective range of distance for the two voltage settings are approximately the same at 2cm, the drop over increasing distance appears to be greater when the power supply is set to 10V. For example, for the distance from 2cm to 3cm, there was a drop in 2V at 10V power supply. This is as opposed to the drop in 1V at 17V power supply over the same distance from 2cm to 3cm. The overall voltage drop was also smaller at 17V, from 5V to 2.5V. At 12V, the overall voltage drop was higher, from 5V to 2.1V. As such, having a higher power supply actually makes the voltage drop smaller. Moreover, it was discovered that during the middle of the experiment, the wires and the electromagnet heated up so much that the insulation actually melted. As such increasing the power supply would not be useful in generating a larger voltage drop. Instead, it yielded an even smaller voltage drop, making it more difficult for the microcontroller to detect.


Experiment 2: Detected Voltage drop versus vertical distance


In the experiment, I kept the power of the electromagnet at a constant voltage of 10V and a driven current of 2.44A, with the sensor positioned above the electromagnet on the vertical axis. The electromagnet is initially programmed to turn on at PWM of 100% for a period of three seconds. Subsequently, the PWM is set to 0% for another three seconds. The result is a sequence of turning on and off of the electromagnet every six seconds. The aim of this experiment is to determine the effective vertical distance where the turning off of the electromagnet will yield the greatest drop in sensor output. The larger the drop in sensor output, the easier it is to detect the electromagnet that the user is actuating with the hall effect sensor. An oscilloscope was used to measure the voltage output of the sensor.

This plot shows that the voltage drop is the greatest at 0 cm. However, given that the height of the spikes is about 2.0cm and the user is not allowed to touch the ferofluid, readings from 0 to 2.0 cm are to be ignored. Therefore, the largest voltage drop (1.9V) that can be detected is at 2.0cm. From 2.0 cm to 4.0 cm, the voltage drop decreases from 1.9 V to 1.0 V but remains within an acceptable range that can be detected. When the distance is greater than 1cm, the voltage drop that can be detected is much smaller. At larger distances, for example at 7.0 cm, the voltage drop that can be detected is only 0.60 V. These attributes can be used to determine the range of vertical distance through the limiting of the threshold detection range. For example, if the microcontroller is to actuate the electromagnets only from a distance from 2.0 cm to 4.0 cm, the threshold should be set from 1.0 V to 1.9 V.

Experiment 3: Hall effect sensor reading versus horizontal distance



Once more keeping the power of the electromagnet constant, the sensor is placed on the vertical axis of the electromagnet at 2.0 cm, since at this distance the sensor is most sensitive, registering the largest change in values with respect to distance moved. Once again, the electromagnet is set to turn on and off every three seconds, from PWM of 100% to 0%. The horizontal distance to the electromagnet is measured with respect to the center of the electromagnet. The detected voltage readings are calculated by subtracting the minimum voltage readings from the maximum voltage readings.

In this experiment, the detected voltage readings are measured versus the horizontal distance to the electromagnet. The aim of this experiment is to determine the range of detected voltage drop that corresponds to the desired horizontal distance to the electromagnet.

The plot shows a decrease in detected voltage drop with increasing horizontal distance with respect to the center of the electromagnet. This decrease can be seen to be steady from the range of 0 cm to 5.0 cm. From 6.0 cm to 7.0 cm, the detected voltage drop is constant at 0.50 V. Therefore, the microcontroller is unable to detect the position of the sensor at a horizontal distance beyond 6.0 cm from the electromagnet.

Given that the radius of the electromagnet is 2.5 cm, the horizontal distance detection range should be set to 1.1 V to 1.6 V which translates to a horizontal detection range from 0 cm to 2.5 cm of the electromagnet. This ensures the actuation of the electromagnet only when the sensor is within the horizontal area enclosed by the electromagnet.