Multiplexing card protection device

Abstract

Protection device for a multiplexing card. The invention relates to a protection device for a multiplexing card for selecting an electrochemical cell to be measured and belonging to an alternating stack of electrochemical cells and interconnectors, said multiplexing card belonging to a set of multiplexing cards of a digital multimeter, and comprising a set of switching relays connected by a wiring matrix, each relay in the closed state electrically connecting said digital multimeter, the electrochemical cell to which it is bijectively associated, said protection device comprising, for each of the relays, a resistive assembly comprising at least one resistor, suitable for being connected between each relay and the bijectively associated electrochemical cell, the value of said resistive assembly being configured to limit the value of the current,suitable for circulating from said cell to the multimeter below a predetermined current value threshold. Figure for the abbreviation: Figure 4,

Description

Title of the invention: Device for protecting a multiplexing card

[0001] The present invention relates to a device for protecting a multiplexing card for selecting an electrochemical cell whose DC voltage is to be measured individually, the electrochemical cell belonging to an alternating stack of a plurality of electrochemical cells and interconnectors, said multiplexing card belonging to a set of multiplexing cards of a digital multimeter, and comprising a set of switching relays connected by a wiring matrix, each switching relay in the closed state being capable of electrically connecting to said digital multimeter, the electrochemical cell of said stack to which it is bijectively associated.

[0002] The present invention also relates to a system for measuring the voltage of an alternating stack of a plurality of electrochemical cells and interconnectors, said system comprising a digital multimeter comprising a plurality of multiplexing cards.

[0003] The invention lies in the field of electrochemical cell voltage measurement. More specifically, the present invention lies in the field of individual cell voltage measurement belonging to a solid oxide stack, of the solid oxide electrolyzer SOEC (Solid Oxide Electrolyzer Ceïï) type, or of the solid oxide fuel cell SOFC (Solid oxide fuel cells) type operating at high temperature.

[0004] The principle of a solid oxide electrolyser 10 SOEC is illustrated by [Fig.l] and consists of transforming, within the same system, water vapour H2O into H2 and O2, and / or, in a manner not shown, CO2 into CO and O2.

[0005] The description of such an electrolyser given below is limited to the H2O / H2 and O2 pair in electrolysis mode, but is directly transposable to the SOFC type fuel cell mode supplied with H2 and O2, or even with CH4 and air.

[0006] As illustrated in [Fig.l], an electrolyzer 10 of this type is an electrochemical device for producing hydrogen and oxygen under the effect of an electric current. In the same way, an SOFC cell offers an inverse operation of the same electrochemical system: it produces an electric current and heat by being supplied with hydrogen, or natural gas, and air. These systems can operate today between 600°C and 1000°C.

[0007] Generally speaking, an electrolyser, as illustrated by [Fig.l], consists of a stack of elementary modules (i.e. electrochemical cell) placed in series with a electrical point of view.

[0008] Such a stack comprises, sandwiched between two interconnection plates, also called hereinafter “interconnectors” 12, a first electrode corresponding to a cathode 14 (i.e. H2 electrode according to the example of [Fig.l]), an electrolyte 16 and a second electrode 18 corresponding to an anode (i.e. O2 electrode according to the example of [Fig.l]). The assembly 20 consisting of the electrolyte 16 with the two electrodes 14 and 18, is hereinafter called an electrochemical cell.

[0009] More precisely, the electrochemical cell 20 or electrolyte-electrode assembly is therefore a ceramic multilayer assembly comprising at least one central ion-conducting layer 16 which is a dense and sealed solid electrolyte, sandwiched between two layers 14 and 18 which constitute porous electrodes. It should be noted that additional layers, not shown, may exist, but only serve to improve one of the already existing layers 14, 16 and 18.

[0010] This electrochemical cell 20 is sandwiched between the two interconnectors 12. A complete electrolyser 10 is then an alternating stack 22 of electrochemical cells 20 and interconnectors 12 capable of producing hydrogen H2 and oxygen O2 under the effect of an electric current 24.

[0011] The interconnection plates or “interconnectors” 12 are electronic conductors which ensure contact between one face with the cathode 14 of a cell and the other face with the anode 18 of the following cell.

[0012] The first role of the interconnectors 12, generally consisting of metal plates, is to supply the cell with electric current 24. In addition, they also serve to distribute the fuels and to recover the gases produced while separating the anode and cathode compartments of two adjacent electrochemical cells 20.

[0013] It is known that in SOEC electrolysis mode, the cathode compartment contains water vapor and hydrogen (and / or CO if CO2 is inlet), product of the electrochemical reaction, while the anode compartment contains a draining gas if it exists and oxygen, another product of the electrochemical reaction both in the case of the electrolysis of water or carbon dioxide.

[0014] It is also known that in SOFC fuel cell mode, the anode compartment contains the fuel and the cathode compartment contains the oxidizer.

[0015] The voltage measurement of each electrochemical cell 20 is important because this individual measurement makes it possible to evaluate the state of health of each cell and to choose the overall operating point of the electrolyser / fuel cell based on the individual response of each electrochemical cell 20.

[0016] Each electrochemical cell voltage 20 is measured individually by connecting, through the interconnectors linked to these electrochemical cells, a voltage measuring device by means of electrical wires.

[0017] Each voltage measuring wire is ultimately connected to a single digital multimeter 26, illustrated in [Fig.2], via a multiplexing card MUX. The digital multimeter 26 performs continuous voltage measurements, the selection of the electrochemical cell to be measured is carried out by multiplexing cards MUX whose role is to select a single electrochemical cell from a multitude of electrochemical cells available in the stack 22 of electrochemical cells.

[0018] In [Fig.2], the digital multimeter 26 comprises for example four multiplexing cards MUX 1, MUX 2, MUX 3, MUX 4.

[0019] Each of the multiplexing cards MUX 1, MUX 2, MUX 3, MUX 4 is, in the example of [Fig.2], a multiplexing card with twenty channels, each associated with two predetermined electrical potentials, one being low defined by the letter L (from the English Low) corresponding for example to the ground or to a potential of 0V, and the other high defined by the letter H (from the English High) representing the potential of the cell to be measured.

[0020] More precisely, the voltage measurement of the electrochemical cells is carried out by two wires for each electrochemical cell, the voltage of each stage (i.e. each electrochemical cell) is measured relative to a reference, this potential being able to be the ground M at 0V for the first cell Cl or the potential of the cell of index Nl for each cell of index N.

[0021] For the multiplexing card MUX 1, the channel Chl LM of the first channel Chl is connected to the ground M, the channel Chl H-TC1 of the first channel Chl and the channel Ch2 L-TC1 of the second channel Ch2 are dedicated to the voltage measurement of a first electrochemical cell Cl of the stack, and connected by a wire F, the letters L and H being respectively associated with the two predetermined electrical potentials mentioned above low (L for low in English) and high (H for high in English) and so on up to the nineteenth cell C19 measured by the channels Chl9 H-TC19 and Ch20 L-TC19 connected by a wire F, the last channel Ch20 H-TC20 of the twentieth channel of the multiplexing card MUX 1 participates in the voltage measurement of the twentieth cell C20, a measurement which is completed by the first channel of the first channel Chl L-TC20 of the second multiplexing card MUX 2, which measures the voltages of cells numbered 21 to 39 via its following eighteen channels,the last channel Ch20 H-TC40 of the twentieth channel of the multiplexing card MUX 2 participates in the voltage measurement of the fortieth cell C40, a measurement which is completed by the first channel of the first channel Chl L-TC40, not shown, of the third multiplexing card MUX 3 and so on up to the seventy-ninth cell via the channels Chl9 H-TC79 and Ch20 L-TC79 of the multiplexing card MUX 4. ,

[0022] Recent work has made it possible to increase both the number and the surface area of electrochemical cells 20, which results in an increase in the overall stack voltage and currents flowing through it. This increase in stack voltage and current has highlighted the fragility of the multiplexing cards.

[0023] Indeed, the historical multiplexing cards were capable of withstanding a voltage level of the order of 60V, a level which is exceeded by the new stacks for the aforementioned reasons. These multiplexing cards have therefore been replaced by a new type of commercial multiplexing cards having a resistance to a higher voltage of the order of 300V.

[0024] However, as illustrated by [Fig.3] this new type of multiplexing card then proves to be more sensitive to the high current of the stack 22. View 28 of [Fig.3] illustrates in particular a multiplexing card with thirty-five channels Chl, Ch2, .. ..Ch35, each channel being associated with two predetermined electrical potentials, one being low defined by the letter L (from the English Low), corresponding for example to the ground or to a potential of 0V, and the other high defined by the letter H (from the English High) representing the potential of the cell to be measured, the channels C_I, C_S, I and S, are respectively conventionally associated with the inputs (from the English C_I for Card Input and I for Input) and with the detection (from the English C_S for Card Sense and S for Sense) but these inputs are not used subsequently for the measurement.

[0025] Indeed, to select a single cell from a multitude of cells available in the stack, the multiplexing card is composed of substantially identical switching relays (i.e. switches) connected by a wiring matrix as illustrated by view 28 of [Fig. 3] schematically representing the internal wiring of a multiplexing card. When no measurement is carried out, the relays, represented by switches, are all open.

[0026] When the first cell Cl is to be measured, the first relay composed of the two switches of the channels HI (for the high electrical potential H of voltage previously mentioned of the channel Chl H-TC1 of [Fig.2]) of the first channel Chl and LO (for the low electrical potential L of voltage previously mentioned of the channel Ch2 L-TC1 of [Fig.2]) of the second channel Ch2 is closed in order to electrically connect the first cell Cl to the multimeter which will evaluate its voltage.

[0027] This relay then opens after a waiting time of the order of a millisecond, the second relay, composed of the two switches of the HI channels (for the high electrical potential H of voltage previously mentioned of the Ch2 H-TC2 channel of [Fig.2]) of the second channel Ch2 and LO of the third channel Ch3, closes allowing the voltage measurement of the second cell C2, then it opens, etc.

[0028] Thus, for the measurement of X cells, the X relays of the multiplexing card respectively associated close then open one after the other.

[0029] The switching speeds of the relays are extremely fast (a few milliseconds), so, as illustrated by the DC link in [Fig. 3], it happens that relay N+1 is closing while relay N is not yet open, thus connecting cell N+1 to cell N, for example cell 2 to cell 1 in [Fig. 2]. In this case, with the two aforementioned relays being closed simultaneously, the cells are in DC short-circuit and deliver high currents in the circuit, which can destroy the two relays on the multiplexing card respectively associated with each cell.

[0030] View 30 of [Fig.3] illustrates the associated voltage measurement when such overcurrent faults occur over time and manifest as voltage peaks P for each affected cell.

[0031] Thus, an overcurrent results in the destruction of the internal relays of the multiplexing card and therefore prevents its nominal operation. To remedy this, current solutions aim to protect a multiplexing card by limiting the current or voltage using a circuit breaker to avoid a short circuit, an overvoltage or an overcurrent. However, the implementation of a circuit breaker implies, when it is activated, a pure and simple interruption of the measurement in progress.

[0032] In other words, currently, there is no type of MUX multiplexing card compatible with both voltage and current, in particular for the aforementioned SOFC / SOEC application, avoiding the introduction of a circuit breaker capable of interrupting the continuous voltage measurement.

[0033] The invention thus aims to remedy the drawbacks of the state of the art by proposing a solution making it possible to protect the multiplexing cards from the occurrence of such an overcurrent while avoiding the use of a circuit breaker.

[0034] To this end, the invention proposes a device for protecting a multiplexing card for selecting an electrochemical cell whose DC voltage is to be measured individually, the electrochemical cell belonging to an alternating stack of a plurality of electrochemical cells and interconnectors, said multiplexing card belonging to a set of multiplexing cards of a digital multimeter, and comprising a set of switching relays connected by a wiring matrix, each switching relay in the closed state being capable of electrically connecting to said digital multimeter, the electrochemical cell of said stack with which it is bijectively associated, said protection device comprising, for each of the relays of said set of switching relays of said multiplexing card, a resistive assembly comprising at least one resistor,suitable for being connected between each relay and the bijectively associated electrochemical cell, the value of said resistive assembly being configured to limit the value of the current, suitable for circulating from said cell to the multimeter via said resistive assembly then via said relay, below a predetermined current value threshold.

[0035] Thus, the present invention proposes to include a device for protecting the multiplexing cards in the electrical voltage measurement circuit. This protection device has the purpose of limiting the current which can flow through the MUX multiplexing card with which it is associated.

[0036] More precisely, the protection device consists of introducing electrical resistances, calculated according to the intended application, in particular SOEC or SOFC, into the measurement circuit in order to limit the current, these resistances being able to be adjustable according to the configuration of the test.

[0037] As previously indicated, the multiplexing cards to which such a protection device is applied, being resistant to the maximum voltage of the stack, the multiplexing cards, after installation of such a protection device, are suitable for use in their operating range, the protection device making it possible to prevent them from being destroyed during use.

[0038] The protection device for a multiplexing card proposed according to the present invention may also have one or more of the characteristics below, taken independently or in any technically conceivable combination:

[0039] - the resistance values ​​of each resistive assembly were chosen so that the current is three times lower than the maximum current value admissible by said multiplexing card;

[0040] - the value R of each resistive assembly is obtained from the following equation:

[0041] \ fm ax /

[0042] with Ue the overall voltage of said stack, Imax the maximum admissible current value, and C a safety coefficient;

[0043] - Imax = 0.5 A, Ue < 300V, and C=3;

[0044] - said resistive assembly comprises only one resistor;

[0045] - the value of said resistive assembly is reconfigurable;

[0046] - the value of said resistive assembly is reconfigurable so as to be applicable to the continuous voltage measurement of an electrochemical cell belonging to a solid oxide stack, of the SOEC solid oxide electrolyser type;

[0047] - the value of said resistive assembly is reconfigurable so as to be applicable to the continuous voltage measurement of an electrochemical cell belonging to a solid oxide stack, of the solid oxide fuel cell (SOFC) type;

[0048] - the protection device is suitable for being encapsulated in a removable housing of the multiplexing card to be protected.

[0049] The invention also relates to a system for measuring the voltage of an alternating stack of a plurality of electrochemical cells and interconnectors, said system comprising a digital multimeter comprising a plurality of multiplexing cards and as many protection devices, according to the present invention as described above, as there are multiplexing cards.

[0050] Other characteristics and advantages of the invention will emerge from the description given below, for information purposes only and in no way limiting, with reference to the appended figures, among which:

[0051] [Fig.l], [Fig.2], [Fig.3] Figures 1 to 3 relating respectively to the structure of a solid oxide stack, the architecture of a digital multimeter, and the schematic representation of the internal wiring of a multiplexing card with the occurrence of an overcurrent as well as the measurement associated with such wiring, have been previously described in relation to the state of the art and the definition of the technical problem which the present invention proposes to remedy and will not be described further subsequently;

[0052] [Fig.4] [Fig.4] comprises a schematic representation of the internal wiring of a multiplexing card with addition of the protection device according to the present invention as well as the measurement as well as the associated voltage measurement acquired over time;

[0053] [Fig.5] [Fig.5] is an exploded view of a removable housing suitable for encapsulating the Multiplexing card protection device according to the present invention.

[0054] In the remainder of the description, the expression “substantially equal to” or “substantially identical” defines a relationship of equality to plus or minus 10%, preferably to plus or minus 5%.

[0055] View 32 of [Fig.4] corresponds first of all to a schematic representation of the internal wiring of a multiplexing card with the addition of the protection device according to the present invention thus forming, in part (the digital multimeter generally comprising several multiplexing cards), the measurement system proposed according to the present invention.The protection device according to the present invention is therefore a device for protecting a multiplexing card for selecting an electrochemical cell whose DC voltage is to be measured individually, the electrochemical cell belonging to an alternating stack of a plurality of electrochemical cells and interconnectors, said multiplexing card belonging to a set of multiplexing cards of a digital multimeter, and comprising a set of switching relays connected by a wiring matrix, each switching relay in the closed state being capable of electrically connecting to said digital multimeter, the electrochemical cell of said stack with which it is bijectively associated, which in comparison with view 28 of [Fig.3] previously described, comprises, for each of the relays of said set of switching relays of said multiplexing card, a resistive set of value R, comprising at least one resistor, and suitable for being connected between each relay and the bijectively associated electrochemical cell, the . value of said resistive assembly being configured to limit the value of the current, capable of flowing from said cell to the multimeter via said resistive assembly then via said relay, below a predetermined current value threshold.

[0056] The voltage measurement system of an alternating stack of a plurality of electrochemical cells and interconnectors according to the present invention comprises a digital multimeter comprising a plurality of multiplexing cards and as many protection devices, as described above, as there are multiplexing cards, view 32 illustrating, for reasons of simplicity, the addition of a single protection device to the associated multiplexing card.

[0057] Such a protection device makes it possible to limit the currents in the range of currents acceptable by the MUX multiplexing cards, in fact as illustrated in view 32 of [Fig.4], in comparison with view 28 of [Fig.3], substantially identical (i.e. similar) resistive assemblies and each with the same value R are added in the circuit of the measurement system.

[0058] Hereinafter, by “resistive assembly”, we mean one or more resistors combined in series or in parallel whose resistive value is configured to limit the value of the current flowing within the relays of the multiplexing card.

[0059] As an optional addition, the resistance values ​​of each resistive assembly have been chosen so that the current is three times lower than the maximum current value admissible by said multiplexing card, and this in accordance with the resistance manufacturing standards.

[0060] As an optional addition, the value R of each resistive assembly is obtained from the following equation: R= ( jx G with Ue the overall voltage of said stack, Imax the maximum current value admissible by the relays of the multiplexing card, and C a safety coefficient.

[0061] According to an optional implementation, Imax = 0.5 A, Ue < 300V, and C=3 so that the safety coefficient makes it possible to ensure that the current is three times lower than the maximum current value admissible by said multiplexing card.

[0062] Preferably and optionally, said resistive assembly comprises only one resistor.

[0063] Advantageously and optionally, the value R of said resistive assembly is reconfigurable. In other words, the protection resistance values ​​are modifiable (i.e. adjustable) for any measurement system and according to the configuration constraints of the solid oxide stacks to be tested. Such protection by resistors of variable value (i.e. adjustable, reconfigurable) in fact allows adjustment according to the nature of the solid oxide stack to be analyzed. Such variable value resistors correspond for example to potentiometers.

[0064] According to a first optional example, the value of said resistive assembly is reconfigurable so as to be applicable to the continuous voltage measurement of an electrochemical cell belonging to a solid oxide stack, of the SOEC solid oxide electrolyser type.

[0065] According to a second optional example, the value of said resistive assembly is reconfigurable so as to be applicable to the continuous voltage measurement of an electrochemical cell belonging to a solid oxide stack, of the solid oxide fuel cell SOFC type.

[0066] By judiciously choosing the resistance value according to the constraints of the multiplexing cards used and / or the solid oxide stack to be tested, and / or the digital multimeter, very small measurement deviations due to the resistances of the protection device according to the present invention are thus obtained, the measurement deviation D due to the protection device being obtained according to the following equation:

[0067] D = -,---j---£—7-—— x 100 Impedance on the multimeter

[0068] For example, the measurement deviation D is of the order of ten microvolts when the measurement precision required for a solid oxide stack to be tested is of the order of a millivolt.

[0069] It should be noted that the protective resistive assemblies (i.e. resistors) can be inserted at any location in the electrical circuit of the measurement system, either between the cells of the solid oxide stack and the multiplexing card while remaining outside the multiplexing card as illustrated by the example in view 32 of [Fig.4] which makes it possible to use the existing multiplexing cards, or in situ, in the multiplexing card as such, upstream of each of its relays which implies a modification of the existing multiplexing cards.

[0070] View 34 of [Fig.4] illustrates the effect of the protection device on the measurement over time, in comparison with view 30 of [Fig.3], the protection device according to the present invention making it possible to avoid overcurrent faults associated with voltage peaks in view 30 of [Fig.3], view 34 representing an NP measurement without a peak (i.e. absence of voltage peak).

[0071] According to an optional and advantageous embodiment, the aforementioned protection device is suitable for being encapsulated in a removable housing of the multiplexing card to be protected, as illustrated by [Fig. 5] corresponding to an exploded view of a removable housing 40 suitable for encapsulating the protection device 42 of the multiplexing card according to the present invention.

[0072] In this view, the protection device 42 comprises a set of resistors 44 connected individually by two wires, and in a manner not shown for reasons of simplicity, to each of the quick connectors 46, for example of the SUBD 25 type, these connectors having a face accessible to the outside of the housing, itself formed of a base 48 and a cover 50, for example made of plastic or any other non-conductive material, to then be connected to the multiplexing card to be protected.

[0073] Thus, according to this optional and advantageous embodiment, the protection resistors 44 are encapsulated in a removable housing 40 with quick connectors 46, which allows reuse and offers a compact protection solution.

[0074] It is noted that the installation of the protection device is however possible in various ways not shown.

[0075] Those skilled in the art will understand that the invention is not limited to the embodiments described, nor to the particular examples of the description, the embodiments and variants mentioned above being suitable for being combined with each other to generate new embodiments of the invention.

[0076] The present invention thus proposes a device for protecting a multiplexing card for a digital multimeter making it possible, due to its resistive nature as detailed previously, to protect the multiplexing cards for the acquisition of data from a test bench of a solid oxide stack, in SOEC electrolysis mode or in SOFC battery mode, whatever the power of the solid oxide stack tested and whatever its configuration, for example with electrochemical cells having a surface area of ​​100 cm2, 200 cm2, and / or whatever the number of electrochemical cells, and / or whatever the power of the solid oxide stack mounted for an electrical test.

[0077] Such a protection device according to the present invention makes it possible to voluntarily limit and control the current or voltage so as not to cut off (i.e. interrupt) the acquisition of data during the test, so that the protection device according to the present invention plays a role of “current / voltage limiter” without ever being in a role of “circuit breaker” as conventionally proposed according to the current state of the art.

[0078] Furthermore, such a protection device is introduced into the measurement system without disturbing the signals acquired (i.e. the measurements as such) during the bench test and without requiring re-calibration of the measurement system, because as indicated previously the measurement deviation introduced by the protection device, when it is connected to the measurement system, is of the order of ten microvolts when the measurement precision required for a solid oxide stack is of the order of a millivolt.

[0079] According to an advantageous optional aspect, such a protection device for a multiplexing card is also configurable to order, by adapting the ohmic impedance of each resistive assembly, as a function of the power of the solid oxide stack to be measured.

[0080] Thus the present invention offers a compact and modular solution for protecting a multiplexing card.

Claims

Claims

1. Protection device (42) for a multiplexing card for selecting an electrochemical cell whose DC voltage is to be measured individually, the electrochemical cell (20) belonging to an alternating stack (22) of a plurality of electrochemical cells and interconnectors, said multiplexing card (MUX 1, MUX 2, MUX 3, MUX 4) belonging to a set of multiplexing cards of a digital multimeter (26), and comprising a set of switching relays connected by a wiring matrix, each switching relay in the closed state being capable of electrically connecting to said digital multimeter, the electrochemical cell of said stack with which it is bijectively associated, characterized in that said protection device comprises, for each of the relays of said set of switching relays of said multiplexing card, a resistive assembly comprising at least one resistor (R, 44),suitable for being connected between each relay and the bijectively associated electrochemical cell, the value of said resistive assembly being configured to limit the value of the current, suitable for flowing from said cell to the multimeter (26) via said resistive assembly then via said relay, below a predetermined current value threshold, the resistance values ​​of each resistive assembly having been chosen so that the current is three times lower than the maximum current value admissible by said multiplexing card.,

2. Protective device (42) according to claim 1, in which the value R of each resistive assembly is obtained from the following equation: \imax / with Ue the overall voltage of said stack, Imax the maximum admissible current value, and C a safety coefficient.

3. Protective device (42) according to claim 2 in which: Imax = 0.5 A, Ue < 300V, and C=3.

4. A protection device (42) according to any preceding claim wherein said resistive assembly comprises only one resistor.

5. A protective device (42) according to any one of the claims previous in which the value of said resistive assembly is reconfigurable.

6. Protection device (42) according to claim 5 wherein the value of said resistive assembly is reconfigurable so as to be applicable to the continuous voltage measurement of an electrochemical cell belonging to a solid oxide stack, of the SOEC solid oxide electrolyser type.

7. Protection device (42) according to claim 5 wherein the value of said resistive assembly is reconfigurable so as to be applicable to the continuous voltage measurement of an electrochemical cell belonging to a solid oxide stack, of the solid oxide fuel cell SOFC type.

8. Protection device (42) according to any one of the preceding claims, characterized in that it is suitable for being encapsulated in a housing (40) removable from the multiplexing card to be protected.

9. System for measuring the voltage of an alternating stack (22) of a plurality of electrochemical cells and interconnectors, said system comprising a digital multimeter (26) comprising a plurality of multiplexing cards and as many protection devices (42), according to any one of the preceding claims, as there are multiplexing cards.

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