Absolute Capacitance Measurement by Direct Digital Fitting of Proportional Coefficient
Round 1
Reviewer 1 Report (Previous Reviewer 3)
Comments and Suggestions for AuthorsThe paper presents a technique for capacitance measurements using a RC circuit. The authors revised the first version of the paper and the work is now improved. In particular, the comparison of the measured capacitance value with a reference value from a commercial instrument allows to better understand the accuracy provided by the proposed technique. However, revisions are nedded before the paper can be considered for publication. Please, address the following issues to improve the paper quality.
1) At lines 50-51 it is written “Capacitive detection using AC excitation features low power consumption, non-contact measurement, and a high signal-to-noise ratio”. I do not understand what “non-contact measurement” means. From my knowledge, capacitance measurements using an alternating voltage stimulus need the electrodes to be applied to the sample under test, thus there is a contact between the sample and the electrodes.
2) At lines 80-81 it is written “A.L. Stott et al. [23] in a discussion of ECT principles introduced ETC systems based on charge-discharge capacitance measurement ….”. Is it ECT or ETC? Moreover, the authors should write the abbreviations extensively the first time that are used.
3) At lines 89-92 it is written “the proportional coefficient is solved by direct fitting according to the property that the difference between the input square-wave signal and the output square-wave response signal is proportional to the slope of the square-wave response function in a first-order RC system”. The output signal Vo is not a square-wave signal but an analog voltage with time constant RC. This issue is also present at line 194, line 235, line 240, and line 291.
4) At lines 152-154 it is written “At this time, the use of two signals superimposed on the signal as a simulated noise source, the two signals were voltage 0.016V, frequency 1006001Hz and voltage 0.003V, frequency 50021Hz”. Why the authors used this particular signal to simulate the electrical noise? Have the authors used Spice for the circuit level simulations? If this is the case, Spice simulators feature a white noise voltage generator that is probably more suitable to simulate the noise.
5) At line 212 “capacitanceis” should be “capacitances”.
6) In the proposed technique the authors used two channels of the microcontroller ADC: one channel to measure Vi and the other channel to measure Vout. What is the reason of measuring Vi? The voltage Vi is a square-wave signal generated by the microcontroller DAC and its value is well known.
7) In equation (16), I think that ‘Vi(n+1) – Vi(n)’ should be ‘Vo(n+1) – Vo(n)’. In fact, since Vi is a square-wave voltage signal, ‘Vi(n+1) – Vi(n) = 0’ for each semi-period of Vi.
8) The Section 3.3 (gross error handling) is not very clear, and it should be discussed in more details.
9) Since the authors state that one of the advantages of the proposed method is the reduced measurement time (because the capacitance should not be completely charged or discharged), it can be interesting to add a comparison between the measurement time achieved with the proposed technique and with the reference charge-discharge method (or at least to give an estimate of the measurement time reduction).
10) At lines 385 there is a reference to Fig. 16 that does not exist. I think it refers to Fig. 11.
Author Response
请参阅附件。
Author Response File: 
Author Response.pdf
Reviewer 2 Report (Previous Reviewer 1)
Comments and Suggestions for AuthorsAuthor(s) seemed not to have understood by connecting the discussion of the presented data to the literature.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report (New Reviewer)
Comments and Suggestions for Authors- The paper explains the use of smoothing functions and error handling, which strengthens the reliability of the results. However, further comparison with existing methods could strengthen the argument for why this method is superior.
- More detail in some figure captions (especially for circuit diagrams) would make them easier to follow without referencing the text.
- It would be beneficial to include a broader range of comparison, especially with other emerging methods, to provide a more balanced view.
- It would be helpful to discuss potential future work or applications where this method could be applied outside of the capacitance generator context.
- Whether any analog filtering or shielding was applied before ADC sampling to complement digital filtering.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report (Previous Reviewer 3)
Comments and Suggestions for AuthorsThe paper has been revised according to the reviewer comments. I only request minor revisions before the paper can be accepted for publication.
1) Equation (4): since UC is expressed as function of t, then in the right side of the equation t2 should be t.
2) Lines 163-164: “the resistance to be measured is 1nF” should be “the capacitance to be measured is 1nF”.
3) Lines 246-247: “square wave response function” should be “analog response function”.
4) Line 278: the word “signal” is repeated.
5) Line 364: “nominal resistance of 3000 pF” should be “nominal capacitance of 3000 pF”.
6) Lines 413-435: please, improve the clarity of this paragraph and use shorter sentences, since it is not easy to follow.
Comments on the Quality of English LanguageI recommend that the authors check the manuscript for errors and typos. I also recommend, as also pointed out in the comments to the authors, that the authors improve the English language in the paragraph at lines 413-435.
Author Response
We are very grateful for your careful reading. The valuable suggestions you put forward have been of great help to the quality of our thesis. According to your suggestions, we made corresponding modifications. In the revised draft, we marked the specific changes in red font. The following is my reply to you:
Comments 1:
Equation (4): since UC is expressed as function of t, then in the right side of the equation t2 should be t.
Response 1:
We were really sorry for our careless mistakes.Thank you for your reminder.
We sincerely thank the reviewer for careful reading.As suggested by the reviewer, we have corrected the "t2" into "t".The change is in equation (4) of the article.
Comments 2:
Lines 163-164: “the resistance to be measured is 1nF” should be “the capacitance to be measured is 1nF”
Response 2:
We were really sorry for our careless mistakes.Thank you for your reminder.
We sincerely thank the reviewer for careful reading.As suggested by the reviewer, we have corrected the "the resistance to be measured is 1nF" into "the resistance to be measured is 1nF".The change is in lines 163-164 of the article.
Comments 3:
Lines 246-247: “square wave response function” should be “analog response function”.
Response 3:
We were really sorry for our careless mistakes.Thank you for your reminder.
We sincerely thank the reviewer for careful reading.As suggested by the reviewer, we have corrected the "square wave response function" into "analog response function".The change is in lines 246-247 of the article.
Comments 4:
Line 278: the word “signal” is repeated.
Response 4:
We were really sorry for our careless mistakes.Thank you for your reminder.We sincerely thank the reviewer for careful reading.We restated this sentence and corrected the mistake.The modified content is:"In order to adapt to the measurement of different capacitance values, the system needs to generate a square wave excitation signal whose square wave excitation times can change over time. For a 12-bit DAC, the digital quantity variation is 0-4095."The change is in lines 276-279 of the article.
Comments 5:
Line 364: “nominal resistance of 3000 pF” should be “nominal capacitance of 3000 pF”.
Response 5:
We were really sorry for our careless mistakes.Thank you for your reminder.
We sincerely thank the reviewer for careful reading.As suggested by the reviewer, we have corrected the "nominal resistance of 3000 pF" into "nominal capacitance of 3000 pF".The change is in line 364 of the article.
Comments 6:
Lines 413-435: please, improve the clarity of this paragraph and use shorter sentences, since it is not easy to follow.
Response 6:
We sincerely appreciate the valuable comments.We restated this passage. Make the sentences clearer and shorter. These changes will not influence the content and framework of the paper. The modified content is:
"Our analysis shows that the direct fitting proportional coefficient method for capacitance measurement offers significant advantages over the traditional time constant method. The period of the excitation signal has minimal impact on the measurement results. Moreover, this method allows for capacitance measurement without requiring the charging and discharging process to reach a zero-full state, making it independent of the initial and final states of the capacitance.
The experimental data also demonstrates another key advantage of the direct fitting method based on the ratio coefficient. Since this method eliminates the need to wait for the completion of charging and discharging, it substantially reduces measurement time compared to traditional approaches. For instance, in the case of measuring an 18,000 pF capacitance, our method can utilize an excitation signal with a period of 6 ms. In contrast, the traditional charge-discharge method requires a more appropriate period of 40 ms. Using a 6 ms period with the traditional method would lead to significant measurement errors and even prevent capacitance measurement. Furthermore, as capacitance increases, the measurement time for the traditional charge-discharge method grows considerably, while our method remains largely unaffected. Within a cycle of the excitation signal, the direct fitting method based on the proportional coefficient saves approximately 34 ms compared to traditional methods. Additionally, at the same sampling frequency, our method requires less sampling data and simplifies capacitance calculation. In practical measurement and calculation scenarios, to obtain more accurate data, we typically use multiple cycles of square wave signal excitation and repeat measurements to take average values. The time saved by this method will increase multi-fold. In conclusion, compared to the traditional charge/discharge method, the capacitance measurement method based on the proportional coefficient shows substantial improvements in measurement time."
The change is in lines 409-434 of the article.
Comments 7:
I recommend that the authors check the manuscript for errors and typos. I also recommend, as also pointed out in the comments to the authors, that the authors improve the English language in the paragraph at lines 413-435.
Response 7:
We sincerely appreciate the valuable comments.We have revised each of the questions you raised one by one. Meanwhile, we have carefully checked for other typos in the text.We have corrected the "Under this condition of simulated noise interference" into "Under these conditions of simulated noise interference".The change is in lines 166-167 of the article.We have corrected the "fig. 2(b)" into "Fig. 2(b)".The change is in line 173 of the article.We have corrected the "due to the DAC and ADC module has the same clock and reference voltage reference" into "due to the DAC and ADC module have the same clock and reference voltage reference".The change is in lines 268-269 of the article.
Reviewer 3 Report (New Reviewer)
Comments and Suggestions for AuthorsThe authors have responded to my concerns
Author Response
We are very grateful for your careful reading. The valuable suggestions you put forward have been of great help to the quality of our thesis. According to your suggestions, we made corresponding modifications. In the revised draft, we marked the specific changes in red font. The following is my reply to you:
Comments 1:
The authors have responded to my concerns
Response 1:
We sincerely appreciate the valuable comments.We are very glad to receive your response.In the revised draft submitted on April 18th, we only made some corrections to the typos. These changes will not influence the content and framework of the paper.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe results section needs to be tight-up with the literature review.
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe main objection that I have with this work is that there seems to be no compelling motivation for the (so called) new method proposed by the authors. There are possibly unnumerable ways in which the value of a capacitor can be deduced depending on the effect it has on a given circuit parameter an the mere fact that a relationship is used rather than another is not sufficient ground for granting publication on a scientific journal. The problem of capacitance measurements is extensive in the sense that, depending on the specific applications and constraints, one method can be preferrable with respect to another for obtaining some well specified goal. For instance, in IOT applications one can search for a method, even among the known ones, that in that specific situation allows to reach a given resolution with the minimum cost or the minimum power consumption and the process involved in obtaining this goal may be of interest for other researchers. However, in this paper, a possible approach is presented for measuring capacitances without reference to any specific context. The claim for low complexity is not sufficient, in itself, to justify a scientific publication. Besides, most often the problem in capacitance measurements, especially in the case of sensors, is the very nature of the quantity to be measured, since non linearity is common and several different definition of (effective) capacitances can be used. Another problem in capacitance measurements is the role of parasitic capacitances that, with the circuit in Fig. 4, is completely neglected and yet, when reaching the tens of pF range (60 pF is the reported minimum capacitance) the very input capacitance of the voltage follower used to obtain "Vo" is bound to produce a significant deviation in the form of an offset in the measurements. Even from the point of view of data analysis and fitting, I do not see any significant contribution, other than (well know) beneficial effects coming from noise and uncorrelated error reduction from averaging. Table 1 lists a set of experimental results, but, unless I am grossly mistaken, no attempt is made to correlate expected errors with measurement parameters.
Author Response
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsPlease, find the comments in the attached PDF.
Comments for author File: Comments.pdf
The English must be improved, since it is not always easy to follow the discussion.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
