Plant electrophysiological analysis system

Abstract

System (1) for electro-physiological analysis of several plants (P), comprising a first acquisition device (2) comprising: a plurality of first electrodes (21, 21') each intended to be connected to a distinct plant to capture a first analog electrical potential (P1, P1'), a first multiplexer (24, 24') each of whose inputs is connected to one of the first electrodes, the first multiplexer being arranged to multiplex said first analog electrical potentials captured by the first electrodes into a first multiplexed analog signal (S1, S1'), and an analog-to-digital converter (3) one of whose inputs (31, 31') is connected to an output of the first multiplexer to receive said first multiplexed analog signal, the analog-to-digital converter being arranged to measure the potential difference (P21,P21') between said first multiplexed analog signal and a reference electrical potential (P2) and to convert the measured potential difference into a digital signal (S21, S21'). Figure to be published with the abbreviation: Fig. 1,

Description

Title of the invention: Electrophysiological analysis system for plants

[0001] The invention relates to the field of electrophysiological analysis of plants. More specifically, the invention relates to a system for electrophysiological analysis of several plants.

[0002] It has been observed that plants emit electrical signals, particularly in the form of action potentials, reflecting their physiological state. By measuring these electrical signals using electrodes and analyzing them, it is thus possible to determine the physiological state of a plant more quickly and reliably than by direct observation means. In addition, if a stress or disease situation is detected, it is also possible to propose, immediately and automatically, corrective actions to remedy it.

[0003] However, existing electrophysiological plant analysis systems are designed for laboratory use and are not suitable for agricultural use. Indeed, the known systems are based, on the one hand, on an electrical signal acquisition system allowing these signals to be digitized for processing and, on the other hand, on a module for processing these digitized signals implementing, in particular, statistical analysis methods. It is therefore necessary to acquire a plurality of electrical signals simultaneously, over long periods. Thus, for agricultural use, it is necessary to install several acquisition devices in a field. This multiplicity of acquisition systems therefore requires the use of a multitude of data transmission cables to allow the acquisition and transmission of the digitized signals to the processing module.Beyond the cost of these cables, the number of cables required detracts from the robustness of the system and its ease of installation and use.

[0004] The invention falls within this context and thus aims to remedy the aforementioned drawbacks, by proposing a system for electrophysiological analysis of plants which is robust, inexpensive and simple to install and use.

[0005] For these purposes, the invention relates to a system for electrophysiological analysis of several plants, comprising a first acquisition device comprising: a. a plurality of first electrodes each intended to be connected to a separate plant to capture a first analog electrical potential, b. a first multiplexer each of whose inputs is connected to one of the first electrodes, the first multiplexer being arranged to multiplex said first analog electrical potentials captured by the first electrodes into a first multiplexed analog signal, and c. an analog-to-digital converter, one input of which is connected to an output of the first multiplexer for receiving said first multiplexed analog signal, the analog-to-digital converter being arranged to measure the potential difference between said first multiplexed analog signal and a reference electrical potential and to convert the measured potential difference into a digital signal.

[0006] It is understood that, thanks to the invention, it is possible to gather within a single digital signal data relating to the electrical signals emitted by several plants. The quantity of data collected by the first acquisition device is therefore increased, while the cost of the system is reduced. In addition, the transmission of this digital signal to a digital processing module can be done via a single transmission means, in particular via a single cable. This increases the robustness of the system while simplifying its installation and operation.

[0007] A multiplexer is understood to mean any electronic circuit making it possible to concentrate on the same output of the circuit different analog signals received on different inputs of the circuit, for example by successive selection of each of the inputs and switching, for a given duration, a switch connecting the selected input to the output to allow the transmission of the analog signal received on this selected input to the output. Alternatively, the multiplexer may include a sample-and-hold device.

[0008] Advantageously, the sampling frequency of the analog-digital converter is determined as a function of the number of inputs of the multiplexer, and therefore of the number of analog electrical potentials multiplexed by the multiplexer.

[0009] Advantageously, the first acquisition device comprises a plurality of filters, each filter being arranged to filter one of the first analog electrical potentials captured by the first electrodes.

[0010] Where appropriate, the first multiplexer is arranged to multiplex the first filtered analog electrical potentials. In other words, each input of the multiplexer is connected to one of the first electrodes via one of the filters. The arrangement of the multiplexer downstream of the filters makes it possible to prevent the multiplexer from disturbing the acquisition of the electrical potentials by the first electrodes. Each of the filters may comprise an analog smoothing filter and / or a filter for protection against electrostatic discharges.

[0011] Advantageously, the first acquisition device comprises a plurality of operational amplifiers, each amplifier being arranged to receive one of the first filtered analog electrical potentials and an electrical potential of reference, the output of this amplifier being connected to one of the inputs of the multiplexer. It has in fact been noted that each switching carried out by the multiplexer increments, by a given value, the voltage at the output of the multiplexer, thus ultimately distorting the value of the signal supplied to the analog-to-digital converter. The amplification of the first electrical potential upstream of the multiplexer thus makes it possible to compensate for this increment.

[0012] In one embodiment of the invention, the first acquisition device comprises a plurality of second electrodes each intended to be connected to one of said separate plants. If necessary, the analog-digital converter comprises a second input connected to each of the second electrodes and to a common reference electrical potential. If desired, the first acquisition device may comprise a plurality of filters, each filter being arranged to filter one of the second analog electrical potentials captured by the second electrodes. In this mode, each component of the multiplexed analog signal is compared to the same common reference electrical potential. Said common reference electrical potential may for example be obtained from a ground of the first acquisition device.

[0013] In another embodiment of the invention, the first acquisition device comprises a plurality of second electrodes each intended to be connected to one of said distinct plants to capture a second analog electrical potential. Where appropriate, the first acquisition device comprises a second multiplexer each of whose inputs is connected to one of the second electrodes, the second multiplexer being arranged to multiplex said second analog electrical potentials captured by the second electrodes into a second multiplexed analog signal forming said reference electrical potential.Each plant is thus connected to a pair of first and second electrodes, this pair of first and second electrodes being connected to the plant so as to measure a linear electric field generated by the superposition of the transient depolarizations of the membranes of the leaf cells and / or by the ion exchanges at the level of the root system. For example, each of the first and second electrodes can be connected to the stem of the plant to be in contact with the phloem or alternatively, one of the electrodes can be connected to the stem of the plant and the other of the electrodes can be connected to an underground bulb of the plant. If appropriate, the analog-to-digital converter can comprise a first and a second input for receiving respectively the first and second multiplexed analog signals obtained from the pairs of electrodes.

[0014] Preferably, the first and second multiplexers are synchronized. For example, the first electrical potential sensed by the first electrode of each pair of electrodes is transmitted to the output of the first multiplexer during a given time interval and the second electric potential sensed by the second electrode of each pair of electrodes is transmitted to the output of the second multiplexer during the same given time interval.

[0015] Advantageously, the analog-to-digital converter comprises an operational amplifier, the operational amplifier being arranged to receive the first analog electrical potential and said reference electrical potential, the analog-to-digital converter comprising an elementary delta-sigma analog-to-digital converter connected to the output of the operational amplifier. By connection between the output of an operational amplifier and an elementary delta-sigma analog-to-digital converter is meant both a single connection between an amplifier with a single output and the converter on which the signal amplified by the amplifier passes and a double connection between an amplifier with a differential output and the converter where the amplified signal is obtained by the difference between the signals passing on each of the lines of the double connection.

[0016] For example, the operational amplifier may be a low-noise programmable gain amplifier (also called PGA). If necessary, the operational amplifier may be arranged to have a gain of at most 24 and to introduce noise whose average level is less than 5 pV and in particular substantially 0.1 pV in the case of an amplifier with a gain of 24. Advantageously, the elementary delta-sigma analog-digital converter is arranged to have a sampling rate greater than 50 SPS (sample per second) or 50 Hz, or even greater than 250 SPS or 250 Hz, and to convert a signal received at the input into a digital signal coded on 24 bits.Where appropriate, the unitary assembly formed by an operational amplifier and an elementary delta-sigma analog-digital converter is arranged to have an effective number of bits (also called ENOB, from the English Effective Number Of Bits) of at least 16, and in particular at least 19 for an amplifier gain of 24 and for a sampling rate of 250 SPS. This combination is particularly suitable for the electro-physiological analysis of plants insofar as the electrical potential differences from the operational amplifiers are low amplitude analog signals (of the order of a microvolt) which can be amplified by the amplifier while introducing little noise and distortion, thanks to a low gain, and which nevertheless be converted by the converter into digital signals with high resolution (of the order of a nanovolt).

[0017] As a variant, and in particular in the case where the system comprises a plurality of operational amplifiers upstream of the analog-to-digital converter, the analog-to-digital converter may be devoid of an operational amplifier and include an elementary delta-sigma analog-to-digital converter connected directly to the output of the first multiplexer, and where appropriate, to the output of the second multiplexer.

[0018] Preferably, the first acquisition device comprises a housing in which the multiplexer, the analog-digital converter, and where appropriate the filters are arranged.

[0019] In one embodiment of the invention, the first acquisition device comprises another plurality of first electrodes each intended to be connected to a separate plant to capture a first analog electrical potential and another first multiplexer each of whose inputs is connected to one of the other first electrodes, the other first multiplexer being arranged to multiplex said first analog electrical potentials captured by the other first electrodes into another first multiplexed analog signal.If necessary, the analog-to-digital converter is a multi-channel analog-to-digital converter, another input of which is connected to an output of the other first multiplexer to receive the other first multiplexed analog signal, the analog-to-digital converter being arranged to measure the potential difference between the other first multiplexed analog signal and a reference electrical potential and to convert the measured potential difference into another digital signal. If desired, the multi-channel analog-to-digital converter is arranged to measure the potential differences between each first multiplexed analog signal and the same common reference electrical potential.

[0020] Advantageously, the electrophysiological analysis system comprises a digital processing module for the digital signal converted by the analog-digital converter of the first acquisition device. This digital processing module may, for example, be arranged to determine a physiological state of the plant(s) connected to the first electrodes by means of the digital signals converted by the multi-channel analog-digital converter. If desired, the digital processing module may be embedded in the first acquisition device, for example by being arranged in the housing. Alternatively, the digital processing module may be remote from the first acquisition device.Where appropriate, the first acquisition device may comprise a memory arranged in the housing, the analog-digital converter comprising a data output connected to said memory, for example via a microcontroller arranged to control the reading and writing of data in said memory, so as to be able to store the converted digital signals in said memory. Alternatively or cumulatively, the first acquisition device may comprise a connector and / or a wireless communication module connected to said data output, for example via a microcontroller arranged to control the shaping and transmission of data via . this output, to transmit the converted digital signals to the data processing module.

[0021] Advantageously, the processing module can be arranged to implement one or more methods for processing the converted digital signal, demultiplexed or not, to determine a physiological state of the plants. It has in fact been observed that the potential differences thus measured and therefore the converted digital signals exhibit variations which are functions of the physiological state of the plant, and in particular of its sunshine, its water stress, its thermal stress, etc. These variations are variations of certain frequency components of these converted digital signals, and in particular variations of low amplitudes of high frequency components.

[0022] The processing module may be arranged to carry out a spectral analysis of the digital signals. For example, the processing module may be arranged to obtain a spectrum from the digital signals (for example by means of a Fourier transform or by a wavelet decomposition) and to determine one or more spectral power indicators from this spectrum, and in particular one or more indicators chosen from the following indicators: a. a spectral frequency front (also called in English: Spectral Edge Frequency or SEF), namely a frequency below which 95% of the total spectral power is concentrated; b. a median frequency (also called in English: Median Edge Frequency or MEF), namely a frequency below which 50% of the total spectral power is concentrated; c. a power index, namely the total spectral power contained in a given frequency band, in particular a power index in the frequency bands known as beta (>0.5 Hz), alpha (0.3-0.4 Hz), theta (0.1-0.2 Hz) and delta (0-0.1 Hz); d. power index ratios, including a ratio of the delta power index and the theta power index; e. spectral entropy (also called Power Spectrum Entropy or PSE).

[0023] Advantageously, the processing module may implement methods for analyzing variations in this or these indicators, in particular to recognize a shift in the spectral frequency front and / or the median frequency according to a given model or a variation in a power index or a ratio of power indices according to a given model, or a variation in the spectral entropy according to a given model. This may, for example, be a method for classifying a variation in this or these indicators from a library of variation models. predetermined, each predetermined variation model being associated with a given physiological state of a plant. Such a classification process could, for example, be implemented by a pattern recognition algorithm based on automatic learning to recognize the models in said library of models.

[0024] The present invention is now described using examples which are solely illustrative and in no way limitative of the scope of the invention, and from the attached illustration:

[0025] [fig. 1] represents a system for electrophysiological analysis of plants according to a embodiment of the invention; and

[0026] [fig.2] represents a system for electrophysiological analysis of plants according to a another embodiment of the invention.

[0027] [fig.l] shows schematically and partially an electrophysiological analysis system 1 according to a first embodiment of the invention.

[0028] The system 1 comprises a first acquisition device 2 comprising a plurality of first electrodes 21 each intended to be connected to a distinct plant P to capture a first analog electrical potential PI and a plurality of second electrodes 22 each intended to be connected to one of said plants P, so that each plant P is connected to a pair of electrodes 21 and 22. For example, for each plant P, the first electrode 21 being for example connected at the level of an upper section of the stem of the plant P to be in contact with the phloem and the second electrode 22 being for example connected at the level of a lower section of the stem of the plant P also to be in contact with the phloem.

[0029] The first acquisition device 2 further comprises other pluralities of first electrodes 21' and second electrodes 22', connected in pairs to plants P.

[0030] Each of the first electrodes 21 and 21' is connected to a filter 23, 23' arranged to smooth the first electrical potential PI, PI' captured by this first electrode and to protect the plant P connected to this first electrode against electrostatic discharges. The second electrodes 22, 22' are also each connected to a filter 23, 23'.

[0031] The first acquisition device 2 comprises multiplexers 24 and 24', the inputs of which are connected, via the filters 23, to the first electrodes 21 and 21'. Each of the multiplexers 24 and 24' is arranged to multiplex the first electrical potentials PI, PI' captured by the first electrodes connected to its inputs into a first multiplexed analog signal SI, SI'.

[0032] The first acquisition device 2 comprises a multi-channel analog-digital converter 3 provided with two first inputs 31 and 31', each connected to the output of one of the multiplexers 24 and 24' to receive the first multiplexed analog signal SI, SI'. The multi-channel analog-to-digital converter 3 is further provided with two second inputs 32 and 32', each connected on the one hand to each of the second electrodes 22, 22' and on the other hand to the same common reference electrical potential P2, obtained for example via a ground of the first acquisition device 2.

[0033] The multi-channel analog-to-digital converter 3 comprises two operational amplifiers 33 and 33' each arranged to receive one of the first multiplexed analog signals SI and SI' from one of the first inputs 32 and 32' and said common reference electrical potential P2 from one of the inputs 32 and 32' and to measure an electrical potential difference P21, P2T between this first multiplexed analog signal PI, PI' and the common reference electrical potential P2. In the example described, each of the operational amplifiers 33, 33' is a low-noise programmable-gain amplifier, also called PGA (Programmable-Gain Amplifier), whose gain can be programmed up to a value of 24 without an average level of the noise introduced into the signal amplified by the amplifier exceeding a value substantially of 2 pV for this gain of 24.

[0034] The analog converter further comprises two elementary analog-digital converters 34, 34' of the delta-sigma type connected to the differential output of one of the operational amplifiers 33 and 33' to convert the measured electrical potential difference P21, P21' into a digital signal S21, S21'. In the example described, each elementary converter of the delta-sigma type 34, 34' is arranged to sample the electrical potential difference P21, P21', for example at a sampling frequency of 250 Hz, so as to obtain a digital signal S21, S21' coded on 24 bits. This combination of low-noise PGAs and delta-sigma type converters makes it possible to obtain an effective number of bits of at least 19 when the PGA gain is set to 24.In this way, the digital signal S21, S21' obtained at the output of the elementary converter 34, 34' has a particularly satisfactory resolution, taking into account the voltage levels observed for the electrical potentials captured by the electrodes. It should be noted that the sampling frequency of the elementary converters 34 and 34' is determined as a function of the number of inputs of the multiplexers 24 and 24'.

[0035] The first acquisition device 2 further comprises a connection unit 4 for connecting to a data transmission network 5 and a battery 7 arranged to supply electricity to the first acquisition device 2 and in particular to define the common reference electrical potential P2. The filters 23 and 23', the multiplexers 24 and 24', the multi-channel analog-to-digital converter 3, the connection unit 4 and the battery 7 are arranged in the same housing 23 of the first acquisition device 2.

[0036] Finally, the system 1 comprises a digital processing module 6, connected to the data transmission network 5 to receive the digital signals S21 and S21' and arranged to implement one or more methods for processing these signals to determine a physiological state of the plants P connected to the first electrodes 21 and 21'. Without this being limiting, the processing module 6 may be arranged to obtain a spectrum from the digital signal S21 and / or S21' (for example by means of a Fourier transform or by a wavelet decomposition) and to determine one or more spectral power indicators from this spectrum, then to implement methods for analyzing the variations of this or these indicators in order to determine the physiological state of the plants P.

[0037] Although the example described in [fig. 1] describes only a single first acquisition device 2, it goes without saying that the analysis system 1 may employ a plurality of acquisition devices, each being similar to the first acquisition device 2 and being connected to one or more other plants, the digital signals converted by these devices all being transmitted to the processing module 6 to be processed there. Similarly, it may be provided that the first acquisition device 2 comprises more than two pluralities of pairs of first and second electrodes, the number of filter - multiplexer - operational amplifier - elementary converter chains corresponding in this case to the number of pluralities of pairs envisaged.

[0038] [Fig. 2] shows, schematically and partially, an electrophysiological analysis system 10 for a plurality of plants P according to a second embodiment of the invention.

[0039] This system 10 is similar, structurally and functionally, to the system 1 described in [fig.l], with the exception of the characteristics described below. It should be noted that a single set of first and second electrodes 21, 22 associated with a multiplexer 24, it being understood that, similarly to [fig.l], the system may comprise other sets of first and second electrodes associated with other multiplexers to power the multi-channel analog-digital converter 3.

[0040] In the example described, each pair of electrodes 21, 22 connected upstream to one of the plants P is connected, downstream, via the filters 23, to an operational amplifier 25, similar to the amplifier 33 of [fig.l]. Each amplifier 25 therefore receives the first filtered analog electrical potential PI and the reference electrical potential P2. The output of each of the amplifiers 25 is connected to one of the inputs of the multiplexer 24. In the example described, the amplifiers 25 being differential amplifiers, the multiplexer 24 is a differential multiplexer and the differential outputs of each amplifier 25 are connected to differential inputs of the multiplexer 24.

[0041] The electrical potential differences P21 measured and amplified by the amplifiers 25 are thus multiplexed by the multiplexer 24. Therefore, in the case where, due to its design, the multiplexer 24 increments, for each switching that it operates, the value of the multiplexed signal SI by a given value, the amplification upstream of the multiplexer 24 makes it possible to make this incrementation without effect.

[0042] It will be noted that in this example, the analog-to-digital converter 3 may include an operational amplifier 33, as shown in [fig.l], or on the contrary, be devoid of one, the multiplexed signals S1 being in this case directly digitally converted.

[0043] The preceding description clearly explains how the invention makes it possible to achieve the objectives it has set itself, and in particular by proposing a system for electrophysiological analysis of plants, an acquisition device of which comprises a multiplexer making it possible to pool on the same multiplexed signal data relating to the electrical signals emitted by different plants. It is thus understood that the quantity of data acquired by the acquisition device can be increased while reducing the number of cables necessary for operating the system, which makes the system more robust and simpler.

[0044] In any event, the invention cannot be limited to the embodiments specifically described in this document, and extends in particular to any equivalent means and to any technically effective combination of these means. In particular, it may be provided to compare the first electrical potentials captured by the first electrodes directly with second electrical potentials captured by the second electrodes, the second inputs of the analog-digital converter not being in this case connected to the same common reference electrical potential. In this case, it may be possible to use second multiplexers arranged to multiplex the second electrical potentials into second multiplexed signals, which are synchronized with the first multiplexers.

Claims

Claims

1. System (1) for electrophysiological analysis of several plants (P), comprising a first acquisition device (2) comprising: • a plurality of first electrodes (21, 21') each intended to be connected to a separate plant to capture a first analog electrical potential (PI, PI'), • a first multiplexer (24, 24') each of whose inputs is connected to one of the first electrodes, the first multiplexer being arranged to multiplex said first analog electrical potentials captured by the first electrodes into a first multiplexed analog signal (SI, SI'), and • an analog-to-digital converter (3) one input (31, 31') of which is connected to an output of the first multiplexer to receive said first multiplexed analog signal, the analog-to-digital converter being arranged to measure the potential difference (P21,P21') between said first multiplexed analog signal and a reference electrical potential (P2) and to convert the measured potential difference into a digital signal (S21, S21').,

2. System (1) according to the preceding claim, in which the first acquisition device (2) comprises a plurality of filters (23, 23'), each filter being arranged to filter one of the first analog electrical potentials (PI, PI') captured by the first electrodes (21, 21'), and in which the first multiplexer (24, 24') is arranged to multiplex the first filtered analog electrical potentials.

3. System (1) according to one of the preceding claims, in which the first acquisition device (2) comprises a plurality of second electrodes (22, 22') each intended to be connected to one of said distinct plants (P) and in which the analog-digital converter (3) comprises a second input (32, 32') connected to each of the second electrodes and to a common reference electrical potential (P2).

4. System (1) according to one of claims 1 to 2, in which the first acquisition device (2) comprises a plurality of second electrodes (22, 22') each intended to be connected to one of said separate plants (P) for capturing a second analog electrical potential and in which the first acquisition device comprises a second multiplexer, each of the inputs of which is connected to one of the second electrodes, the second multiplexer being arranged to multiplex said second analog electrical potentials captured by the second electrodes into a second multiplexed analog signal forming said reference electrical potential.

5. System (1) according to the preceding claim, in which the first and second multiplexers are synchronized.

6. System (1) according to one of the preceding claims, in which the analog-digital converter (3) comprises an operational amplifier (33, 33'), the operational amplifier being arranged to receive the first analog electrical potential (PI, PI') and said reference electrical potential (P2), the analog-digital converter comprising an elementary delta-sigma analog-digital converter (34, 34') connected to the output of the operational amplifier.

7. System (1) according to one of the preceding claims, in which the first acquisition device (2) comprises another plurality of first electrodes (21, 21') each intended to be connected to a separate plant (P) to capture a first analog electrical potential (PI, PI') and another first multiplexer (24, 24') each of whose inputs is connected to one of the other first electrodes, the other first multiplexer being arranged to multiplex said first analog electrical potentials captured by the other first electrodes into another first multiplexed analog signal (SI, SI'), and in which the analog-to-digital converter (3) is a multi-channel analog-to-digital converter of which another input (31, 31') is connected to an output of the other first multiplexer to receive the other first multiplexed analog signal,the analog-to-digital converter being arranged to measure the potential difference (P21, P21') between the other first multiplexed analog signal and a reference electrical potential (P2) and to convert the measured potential difference into another digital signal (S21, S21').,

8. System (1) according to one of the preceding claims, characterized in that it comprises a digital processing module (6) for the digital signal (S21, S21') converted by the analog converter digital signal (3) of the first acquisition device (2), the processing module being arranged to implement one or more methods of processing this digital signal to determine a physiological state of said plants (P) connected to said first electrodes (21, 21').

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