Week 9, 17 March

The output pressure graph was plotted and I found that there is still a lot of noise coupling into the sensor. After discussing with Dr. Cheok, I realized that my grounding design is imperfect.

noisy_sensor

Output Pressure with Noise

Noise is mainly caused by the fluctuating ground. The ground, which is supposed to be 0V, is fluctuating in between 0V to 70mV. This causes the analog output signal to be oscillatory because the ground, as reference point, is not stable. When the noise couples into the sensor ground, the sensor output voltage fluctuates accordingly. This presents a bad feedback towards the control loop.

The grounding has to be designed in such a way that the power ground should be separated completely from other grounds, and only connects to the ground of power supply in parallel with the signal ground. Any fluctuations at the power ground will be compensated by the power supply, and thus noise will not propagate towards the signal ground. In overall, the grounding design is shown below.

grounding_design

Grounding Design

This is my new PCB design with the grounding redesigned.

new_signal_ground

Signal Ground on Main Circuit Board

new_power_ground

Power Ground on an Isolated Board

The output signal for the sensor seems to be a lot more stable with the new grounding design. The output pressure graph is plotted below.

not_noisy_sensor

Output Pressure After Improvement

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