the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Development of an Expendable Current Profiler Based on Modulation and Demodulation
Keyu Zhou
Guangyuan Chen
Zucan Lin
Yunliang Liu
Pengyu Li
Abstract. We designed a low-cost expandable current profiler including software and hardware. An expendable current profiler (XCP) is an observation instrument that rapidly measures currents based on the principle that currents cut the geomagnetic field to induce electric fields. It is important to reduce the cost of an XCP because it is a single-use device. The digitization of the previously developed XCP is carried out underwater, which requires the probe to contain not only analogue circuits for acquiring signals but also digital circuits and digital chips, which are relatively expensive. In this study, an XCP has been developed that adopts signal modulation and demodulation to transmit analogue signals on an enamelled wire, and the signal digitization occurs above the surface of the water. The cost of the instrument is effectively reduced by half while maintaining the ability to measure parameters such as sea current and temperature in real-time. After comparison with data processed from laboratory tests, the acquisition circuit showed accuracy within one-thousandth of one per cent, and the XCP analogue circuit developed for the overall system was stable and reliable. The system exhibited an acquisition accuracy higher than 50 nV for 16 Hz, and the quality of the acquired signal met the requirements for an XCP instrument.
Keyu Zhou et al.
Status: closed
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RC1: 'Comment on gi-2022-22', Anonymous Referee #1, 05 Jan 2023
This manuscript describes the technical realization of the XCP, which is used for marine exploration. The paper explains that the instrument developed in the study successfully addresses several shortcomings of XCP currently available, including reducing the cost and limitations in data acquisition accuracy. The experimental part shows that the accuracy is within 1/1000 and the system can be applied to perform actual field measurements. And prepare for mass production in the future. It is strongly recommended to make minor modifications to be accepted. I have attached below comments arising from the manuscript, which might be helpful to further improve the quality of the paper.
- Please use the capital letters V for voltage and check all figures.
- Please insert a space between the numeral and unit, such as mV, μV, and so on.
- Do you investigate how the operation of the ship affect wireless communication?
- Calibration is introduced in this paper. Each XCP needs to be calibrated one by one before use, which is a bit time-consuming. Is there a simple way to deal with it?
- I recommend enhancing the Conclusions by mentioning limitations of the instrument developed in your study or potential barriers to its use.
Citation: https://doi.org/10.5194/gi-2022-22-RC1 -
AC1: 'Reply on RC1', Qisheng Zhang, 31 Jan 2023
- Thank you so much for your careful check, we apologize for the format problems and we revised that.
- Thank you so much for your careful check, we apologize for the format problems again and that has been corrected.
- We are grateful for your suggestion. The ship definitely affects wireless communication, and we tried to investigate it but it would take very complicated calculation, which will cause the software to run slowly and prone to errors, so we think the best way is to avoid this impact. As a result, on line 157 on page 9, we can see: ‘As the operation of the ship will interfere with wireless communication, after we release the buoy, the buoy will have a timing of 180 seconds before releasing the probe, as shown in Figure 8. As the expendable instruments are operated in a non-stop way, the ship has gone far within 180 seconds, which will not affect the wireless data transmission. As mentioned in the previous section, our wireless transmission distance can reach 2500 meters, and the ship can not travel beyond 2500 meters within 180 seconds. Therefore, the problem of hull interference with wireless communication is ingeniously solved.’ That is how we solved that problem. This is the best solution we can get after considering performance, method and cost.
- Thank you for pointing out the calibration related problems. We are sorry that because every component is not exactly the same, such as resistors, capacitors and chips, there are certain differences in resistance, capacitance and performance. Although this difference may be very small, it does exist. Moreover, our magnification is relatively large, which may amplify these differences. Therefore, in order to ensure the accuracy of the measurement results, we need to accurately calibrate each XCP before leaving the factory, and write the parameters on the package of the product for the user to view.
- We appreciate raising this point. We added the shortcomings of the XCP developed in this paper. For example, our calibration method needs to improvement, and the measurement parameters are not increased. In future, we will improve accuracy, study the effect of increasing the measurement parameters and measurement distance and improve the data transmission mode.
Citation: https://doi.org/10.5194/gi-2022-22-AC1
-
RC2: 'Comment on gi-2022-22', Anonymous Referee #2, 31 Jan 2023
This manuscript describes the software and hardware development of a new low-cost XCP, and compares the consistency and accuracy with the previously developed XCP in the laboratory. It proves that the quality of the acquired signal met the requirements for an XCP instrument. The new XCP has the prospect of mass production. The author finished a good job, but It is suggested to make minor modifications and provide the supporting data. I have the following suggestions for improving the paper.
1、The XCP developed in this paper saves cost by reducing the main control chip of probe and buoy. However, because XCP is disposable, it does not require much performance and long-term reliability, so the price of the main control chip is also low. At the same time, the XCP adds modulation and demodulation circuits and hardware, so does the XCP solve the problem of high cost?
2、Only the comparison between the studied XCP and the previously developed XCP is carried out in the laboratory, it is recommended to compare it with mature product to better reflect the performance of the instrument.
3、The resistive attenuation network is added at the signal input side, and the thermal noise of the resistance itself may also affect the measurement accuracy of the input signal, whether it is considered.Citation: https://doi.org/10.5194/gi-2022-22-RC2 -
AC2: 'Reply on RC2', Qisheng Zhang, 06 Feb 2023
We truly appreciate the time and energy you dedicated in carefully reviewing our manuscript.
Your comments were highly helpful. We really appreciate your attention and comments on our manuscript. Our replies are listed as follows:
1、 We appreciate the reviewer for raising this point. XCP measured the induced electric field generated by the current cutting the geomagnetic field, which is a considerably small signal at a nanovolt level; therefore, if we want to measure accurate current information, we need to have certain requirements for the accuracy and stability of the instrument. The measurement adopts the method of measuring frequency, which needs to generate frequency signals and to compare and simultaneously measure the frequency and phase of multiple signals, including a lot of calculations. This will require a lot of resources; therefore, it is necessary to use the main control chip considering certain resources and performance, which also determines the price of the main control chip. The added modulation and demodulation part of XCP is mainly composed of amplifiers and resistance-capacitors. In this design, four operational amplifiers are used, and four amplifiers are integrated in one chip; therefore, the number of chips added is not large, that is, only two chips are added. In addition, the modulation and demodulation part needs counters. As shown in Figure 6 in this paper, there are two types of chips (CD4046 and CD4040), which are extremely low in cost. In addition, we have also replaced and optimized some other components of the whole system and selected the scheme with the best cost performance. Therefore, the cost of the system is lower.
2、Your suggestion is highly valued, and we express our gratitude for helping us improve our work. The previously developed XCP in the laboratory has been proved its performance. The previous XCP developed in the laboratory has gone through many ocean experiments and has been compared with other mature products (Doppler velocimeter). The results indicated that the XCP has stable performance and performs accurate measurement, which has been reflected in a previous study (Liu, 2017). Therefore, the previous XCP developed in the laboratory has a certain reference value. To better verify the performance of XCP considered in this study, we carried out further experiments comparing with a Nortek Vectrino Profiler Acoustic Doppler Velocimetry according to your suggestions and reflected the experimental results in the paper.
3、 Thank you for pointing out the thermal noise-related problems. In fact, we have considered the noise caused by the resistance of the attenuation circuit. The resistance thermal noise voltage is proportional to the resistance value, bandwidth, and square root of the temperature (Kelvin). In essence, the resistance thermal noise is unavoidable. However, to minimize the noise caused by resistance, we should avoid selecting resistors with larger resistance values. Through actual measurement and experiment, we found that the influence of resistance thermal noise can be ignored. In addition, the reason for designing the attenuation circuit is that an instrument that can generate small signals at the level of nanovolts is not available in the laboratory, and the attenuation network will only be used in the calibration and measurement in the laboratory. In the actual ocean test, originally, the signal is generated at the level of nanovolts; therefore, the attenuation network is not required in the actual ocean application.
Citation: https://doi.org/10.5194/gi-2022-22-AC2
-
AC2: 'Reply on RC2', Qisheng Zhang, 06 Feb 2023
Status: closed
-
RC1: 'Comment on gi-2022-22', Anonymous Referee #1, 05 Jan 2023
This manuscript describes the technical realization of the XCP, which is used for marine exploration. The paper explains that the instrument developed in the study successfully addresses several shortcomings of XCP currently available, including reducing the cost and limitations in data acquisition accuracy. The experimental part shows that the accuracy is within 1/1000 and the system can be applied to perform actual field measurements. And prepare for mass production in the future. It is strongly recommended to make minor modifications to be accepted. I have attached below comments arising from the manuscript, which might be helpful to further improve the quality of the paper.
- Please use the capital letters V for voltage and check all figures.
- Please insert a space between the numeral and unit, such as mV, μV, and so on.
- Do you investigate how the operation of the ship affect wireless communication?
- Calibration is introduced in this paper. Each XCP needs to be calibrated one by one before use, which is a bit time-consuming. Is there a simple way to deal with it?
- I recommend enhancing the Conclusions by mentioning limitations of the instrument developed in your study or potential barriers to its use.
Citation: https://doi.org/10.5194/gi-2022-22-RC1 -
AC1: 'Reply on RC1', Qisheng Zhang, 31 Jan 2023
- Thank you so much for your careful check, we apologize for the format problems and we revised that.
- Thank you so much for your careful check, we apologize for the format problems again and that has been corrected.
- We are grateful for your suggestion. The ship definitely affects wireless communication, and we tried to investigate it but it would take very complicated calculation, which will cause the software to run slowly and prone to errors, so we think the best way is to avoid this impact. As a result, on line 157 on page 9, we can see: ‘As the operation of the ship will interfere with wireless communication, after we release the buoy, the buoy will have a timing of 180 seconds before releasing the probe, as shown in Figure 8. As the expendable instruments are operated in a non-stop way, the ship has gone far within 180 seconds, which will not affect the wireless data transmission. As mentioned in the previous section, our wireless transmission distance can reach 2500 meters, and the ship can not travel beyond 2500 meters within 180 seconds. Therefore, the problem of hull interference with wireless communication is ingeniously solved.’ That is how we solved that problem. This is the best solution we can get after considering performance, method and cost.
- Thank you for pointing out the calibration related problems. We are sorry that because every component is not exactly the same, such as resistors, capacitors and chips, there are certain differences in resistance, capacitance and performance. Although this difference may be very small, it does exist. Moreover, our magnification is relatively large, which may amplify these differences. Therefore, in order to ensure the accuracy of the measurement results, we need to accurately calibrate each XCP before leaving the factory, and write the parameters on the package of the product for the user to view.
- We appreciate raising this point. We added the shortcomings of the XCP developed in this paper. For example, our calibration method needs to improvement, and the measurement parameters are not increased. In future, we will improve accuracy, study the effect of increasing the measurement parameters and measurement distance and improve the data transmission mode.
Citation: https://doi.org/10.5194/gi-2022-22-AC1
-
RC2: 'Comment on gi-2022-22', Anonymous Referee #2, 31 Jan 2023
This manuscript describes the software and hardware development of a new low-cost XCP, and compares the consistency and accuracy with the previously developed XCP in the laboratory. It proves that the quality of the acquired signal met the requirements for an XCP instrument. The new XCP has the prospect of mass production. The author finished a good job, but It is suggested to make minor modifications and provide the supporting data. I have the following suggestions for improving the paper.
1、The XCP developed in this paper saves cost by reducing the main control chip of probe and buoy. However, because XCP is disposable, it does not require much performance and long-term reliability, so the price of the main control chip is also low. At the same time, the XCP adds modulation and demodulation circuits and hardware, so does the XCP solve the problem of high cost?
2、Only the comparison between the studied XCP and the previously developed XCP is carried out in the laboratory, it is recommended to compare it with mature product to better reflect the performance of the instrument.
3、The resistive attenuation network is added at the signal input side, and the thermal noise of the resistance itself may also affect the measurement accuracy of the input signal, whether it is considered.Citation: https://doi.org/10.5194/gi-2022-22-RC2 -
AC2: 'Reply on RC2', Qisheng Zhang, 06 Feb 2023
We truly appreciate the time and energy you dedicated in carefully reviewing our manuscript.
Your comments were highly helpful. We really appreciate your attention and comments on our manuscript. Our replies are listed as follows:
1、 We appreciate the reviewer for raising this point. XCP measured the induced electric field generated by the current cutting the geomagnetic field, which is a considerably small signal at a nanovolt level; therefore, if we want to measure accurate current information, we need to have certain requirements for the accuracy and stability of the instrument. The measurement adopts the method of measuring frequency, which needs to generate frequency signals and to compare and simultaneously measure the frequency and phase of multiple signals, including a lot of calculations. This will require a lot of resources; therefore, it is necessary to use the main control chip considering certain resources and performance, which also determines the price of the main control chip. The added modulation and demodulation part of XCP is mainly composed of amplifiers and resistance-capacitors. In this design, four operational amplifiers are used, and four amplifiers are integrated in one chip; therefore, the number of chips added is not large, that is, only two chips are added. In addition, the modulation and demodulation part needs counters. As shown in Figure 6 in this paper, there are two types of chips (CD4046 and CD4040), which are extremely low in cost. In addition, we have also replaced and optimized some other components of the whole system and selected the scheme with the best cost performance. Therefore, the cost of the system is lower.
2、Your suggestion is highly valued, and we express our gratitude for helping us improve our work. The previously developed XCP in the laboratory has been proved its performance. The previous XCP developed in the laboratory has gone through many ocean experiments and has been compared with other mature products (Doppler velocimeter). The results indicated that the XCP has stable performance and performs accurate measurement, which has been reflected in a previous study (Liu, 2017). Therefore, the previous XCP developed in the laboratory has a certain reference value. To better verify the performance of XCP considered in this study, we carried out further experiments comparing with a Nortek Vectrino Profiler Acoustic Doppler Velocimetry according to your suggestions and reflected the experimental results in the paper.
3、 Thank you for pointing out the thermal noise-related problems. In fact, we have considered the noise caused by the resistance of the attenuation circuit. The resistance thermal noise voltage is proportional to the resistance value, bandwidth, and square root of the temperature (Kelvin). In essence, the resistance thermal noise is unavoidable. However, to minimize the noise caused by resistance, we should avoid selecting resistors with larger resistance values. Through actual measurement and experiment, we found that the influence of resistance thermal noise can be ignored. In addition, the reason for designing the attenuation circuit is that an instrument that can generate small signals at the level of nanovolts is not available in the laboratory, and the attenuation network will only be used in the calibration and measurement in the laboratory. In the actual ocean test, originally, the signal is generated at the level of nanovolts; therefore, the attenuation network is not required in the actual ocean application.
Citation: https://doi.org/10.5194/gi-2022-22-AC2
-
AC2: 'Reply on RC2', Qisheng Zhang, 06 Feb 2023
Keyu Zhou et al.
Keyu Zhou et al.
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