# Mitigating Electrochemical Effects in Resistive Frost-Detection Sensors
## 5 Conclusions  
The comparative analysis between continuous and pulsed DC excitation methods revealed clear advantages of the pulsed approach regarding measurement stability and electrode preservation. Descriptive statistics--mean, standard deviation, coefficient of variation, and variance--were used to evaluate performance. Pulsed DC excitation yielded significantly lower variance, standard deviation, and coefficient of variation, indicating more consistent and reliable sensor performance under the same environmental conditions. The mean resistance for the pulsed method was 14.77 k\(\Omega\), with a standard deviation of 0.47 k\(\Omega\) and a coefficient of variation of 3.17%, in contrast to the continuous method's 5.11 k\(\Omega\) mean, 4.34 k\(\Omega\) standard deviation, and 84.97% coefficient of variation. Variance further highlighted this difference, with 0.22 k\(\Omega^{2}\) for pulsed versus 18.83 k\(\Omega^{2}\) for continuous excitation. The paired-samples \(t\)-test further confirmed the statistical significance of these differences (\(t=196.50,p<0.001\)). Moreover, the continuous excitation method exhibited visual signs of electrode degradation, while the pulsed method did not. This was achieved by limiting voltage application to short intervals (50 ms ON time) with a 1.7% duty cycle for an acquisition rate of 0.33 Hz. The pulsed DC method significantly reduced electrolysis effects, preventing the visible formation of O\({}_{2}\) and H\({}_{2}\) gas, H\({}^{+}\) and OH\({}^{-}\) ions, as well as copper(II) hydroxide (Cu(OH)\({}_{2}\)) and copper(II) oxide (CuO) deposits. This reduction in electrochemical byproducts also helped maintain electrode integrity, ensuring more stable and reliable sensor operation. \begin{table}
\begin{tabular}{c p{284.5 pt}} \hline \hline \(t=0:30\) h & Ions dissolving in the distilled water rapidly decrease water resistivity. \\ \hline \(t=1:00\) h & Resistivity slowly increases as copper(II) oxide and copper(II) hydroxide form on the electrodes, neutralizing ions and thus increasing water conductivity. \\ \hline \(t=1:30\) h & Resistivity reaches a local maximum. \\ \hline \(t=2:30\) h & Resistivity drops abruptly as copper(II) hydroxide dislodges from the electrode, creating a connection between the cathode and anode. \\ \hline \(t=3:30\) h & Resistivity remains low as electron movement occurs primarily through the bridging connection between electrodes, which halts gas production and the formation of Cu(OH)\({}_{2}\) and CuO. \\ \hline \(t=4:30\) h & The connection between the cathode and anode persists, keeping resistivity low, with minimal gas production and copper oxide/hydroxide formation. \\ \hline \(t=5:30\) h & The material bridging the electrodes detaches, and precipitates towards the bottom of the flask. As the water had time for ions to cancel out, its resistivity is high, and therefore a spike in resistance is observed. Gas and ion production resumes, resulting in a drop in resistivity once again. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Explanation for the observations made in the electrodes during testing for the continuously powered sensor reading method. The degradation effects were further confirmed through quantitative image analysis. Measurements of dark material accumulation on the cathode (black pixels) and blue substance formation on the anode (remaining non-black/non-red pixels) supported the visual inspection. In both cases, the sensor powered using the continuous DC excitation method exhibited a clear increase in deposition over time, while the pulsed DC excitation method maintained consistently low values. Although the pulsed DC excitation method caused some resistance changes, these were gradual and predictable, making it suitable for integration into demand defrost systems. In contrast, the continuous voltage method produced erratic fluctuations, introducing noise that could result in false-positive or false-negative readings in automated systems.