Control circuit for peak injection current and eit device

Abstract

The application discloses a kind of injection current peak control circuit and EIT equipment, the control circuit includes: a sampling circuit, it is connected to the output end of current source, for gathering the current signal output by the current source, and conversion into voltage signal;Current peak holding circuit is connected to the output end of the sampling circuit, and the current signal can be kept at current peak;Overcurrent protection circuit includes a switch unit in series in the output end of the current source, and can cut off the switch unit when the current signal output by the current source is higher than threshold current;A main control unit is connected with the current peak holding circuit and the overcurrent protection circuit respectively, for controlling the working state of current peak holding circuit and the overcurrent protection circuit.Compared with prior art, the application can realize the detection and keeping of current peak, and disconnect the current path when the current peak exceeds the threshold value, to realize overcurrent protection.

Description

TECHNICAL FIELD

[0001] The present application relates to EIT electrical impedance tomography equipment, and particularly to a current injection peak value control circuit and EIT equipment. BACKGROUND

[0002] EIT electrical impedance tomography equipment has a current excitation source, which injects current into the human body through a switch matrix, and a collection circuit collects voltage signals at different positions of the human body, and through an image reconstruction algorithm, electrical impedance tomography can be achieved. When injecting current into the human body, if the current injected into the human body exceeds the standard, it is easy to cause the risk of electric shock, so it is necessary to ensure that the injected current of the EIT electrical impedance tomography equipment is below the threshold value.

[0003] Therefore, how to design a current injection peak value control circuit and EIT equipment can avoid the current injected into the human body exceeding the standard, thereby protecting the human body from the risk of electric shock, which is a technical problem to be solved in the industry. SUMMARY

[0004] In view of the problem in the prior art that the current injected into the human body exceeds the standard and easily causes the risk of electric shock, the present application provides a current injection peak value control circuit and EIT equipment.

[0005] The technical scheme of the present application is to provide a current injection peak value control circuit, which comprises: a sampling circuit connected to the output end of a current source, for collecting the current signal output by the current source and converting it into a voltage signal;

[0006] a current peak value maintaining circuit connected to the output end of the sampling circuit and capable of maintaining the current signal at a current peak value;

[0007] an overcurrent protection circuit comprising a switch unit connected in series to the output end of the current source and capable of cutting off the switch unit when the current signal output by the current source is higher than a threshold current;

[0008] a main control unit connected to the current peak value maintaining circuit and the overcurrent protection circuit, respectively, for controlling the working state of the current peak value maintaining circuit and the overcurrent protection circuit.

[0009] Further, the sampling circuit comprises a sampling resistor, an instrument amplifier, and an operational amplifier;

[0010] The sampling resistor is connected in series to the output end of the current source, the input end of the instrument amplifier is connected to both ends of the sampling resistor, the output end of the instrument amplifier is connected to the input end of the operational amplifier, and the output end of the operational amplifier is connected to the current peak value maintaining circuit as the output end of the sampling circuit.

[0011] Further, the current peak holding circuit comprises a first comparator, a logic AND gate and a digital potentiometer.

[0012] The inverting input terminal of the first comparator is connected to the output terminal of the sampling circuit, the non-inverting input terminal is connected to the output terminal of the digital potentiometer, the output terminal of the first comparator is connected to the first input terminal of the logic AND gate, the second input terminal of the logic AND gate is connected to the master control unit, and the output terminal is connected to the CS pin of the digital potentiometer. The U / D pin of the digital potentiometer is connected to the master control unit.

[0013] Further, when the CS pin of the digital potentiometer is at low level and the U / D pin is at high level, the voltage signal output by the digital potentiometer is raised;

[0014] When the CS pin and the U / D pin of the digital potentiometer are both at low level, the voltage signal output by the digital potentiometer is lowered;

[0015] When the CS pin of the digital potentiometer is at high level, the voltage signal output by the digital potentiometer is in a holding state.

[0016] Further, when the digital potentiometer works in the reset mode, the master control unit sends a low level signal to the U / D pin;

[0017] When the digital potentiometer works in the peak holding mode, the master control unit sends a high level signal to the U / D pin.

[0018] Further, the overcurrent protection circuit further comprises a digital-to-analog converter and a second comparator.

[0019] The input terminal of the digital-to-analog converter is connected to the master control unit, and the output terminal is connected to the non-inverting input terminal of the second comparator. The inverting input terminal of the second comparator is connected to the output terminal of the current peak holding circuit, and the output signal of the second comparator is used as an enable signal for controlling the on-off state of the switch unit.

[0020] Further, when the second comparator outputs a high level signal, the switch unit is closed;

[0021] When the second comparator outputs a low level signal, the switch unit is opened.

[0022] Further, the threshold current is a threshold value of the current source injected into the human body.

[0023] Further, the switch unit adopts a single-pole single-throw switch.

[0024] The application further provides an EIT device, wherein the TIT device has the control circuit.

[0025] Compared with the prior art, the application has at least the following beneficial effects:

[0026] The current peak holding circuit and the sampling circuit can detect and hold the injected current peak value of the human body. In addition, the overcurrent protection circuit can avoid the current injected into the human body exceeding the threshold value, avoid the electric shock problem, and set the threshold of the current injected into the human body, so that the product application of different levels of safety current can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only some embodiments of the application, and for those skilled in the art, other drawings can be obtained without creative labor.

[0028] Figure 1 The control block diagram of the current peak injection control circuit of the application;

[0029] Figure 2 The control principle diagram of the sampling circuit of the application;

[0030] Figure 3 The control principle diagram of the current peak holding circuit;

[0031] Figure 4 The working mode schematic diagram of the digital potentiometer;

[0032] Figure 5 The control principle diagram of the overcurrent protection circuit. DETAILED DESCRIPTION

[0033] In order to make the technical problems, technical solutions and beneficial effects of the application more clear, the following will further describe the application in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the application, and are not used to limit the application.

[0034] Therefore, one feature described in the specification will be used to explain one feature of one embodiment of the application, and it is not implied that each embodiment of the application must have the explained feature. In addition, it should be noted that the specification describes many features. Although some features can be combined together to show possible system design, these features can also be used in other combinations which are not explicitly described. Therefore, unless otherwise stated, the described combination is not intended to be limited.

[0035] The principles and structures of the present application will be described in detail below in combination with the drawings and examples.

[0036] The EIT electrical impedance imaging device has a current excitation source, which injects current into the human body through a switch matrix, and a collection circuit collects voltage signals at different positions of the human body, and electrical impedance imaging can be realized through an image reconstruction algorithm. When injecting current into the human body, if the current injected into the human body exceeds the standard, it is easy to cause the risk of electric shock, so it is necessary to ensure that the injected current of the EIT electrical impedance imaging device is below the threshold value. The idea of the present application is to provide a control circuit for the peak value of the injected current, which can disconnect the path of the current injected into the human body when the current injected into the human body exceeds the standard through the setting of the overcurrent protection circuit, thereby realizing the overcurrent protection of the human body.

[0037] The present application provides a control circuit for the peak value of the injected current, which comprises a sampling circuit, a current peak value maintaining circuit, an overcurrent protection circuit and a main control unit.

[0038] The sampling circuit is connected to the output end of the current source, used for collecting the current signal output by the current source and converting it into a voltage signal for subsequent determination of the current peak value.

[0039] The current peak value maintaining circuit is connected to the output end of the sampling circuit, which obtains the voltage signal of the current source through the sampling circuit, and maintains the output unchanged when the voltage signal is maximum. Since the voltage signal of the sampling circuit is converted from the current signal output by the current source, the current signal is also at the current peak value when the voltage signal is maximum. At this time, maintaining the output of the current peak value maintaining circuit unchanged can maintain the output current of the current source at the current peak value at all times, and serve as the current signal output to the human body.

[0040] The overcurrent protection circuit comprises a switch unit connected in series at the output end of the current source, and the switch unit can cut off the switch unit when the current signal output by the current source is higher than the threshold current, thereby disconnecting the output of the current source and avoiding the problem of high current signal damaging the human body.

[0041] The main control unit is connected with the current peak value maintaining circuit and the overcurrent protection circuit respectively, used for controlling the working state of the current peak value maintaining circuit and the overcurrent protection circuit.

[0042] The present application can at least realize the detection and maintenance of the current peak value, and the protection of the peak current overcurrent, thereby improving the safety of the EIT device.

[0043] Please refer to Figure 1, VCCS is a current source, Shunt Resistor is a sampling resistor, AMP is an integrated operational amplifier, Comparator is a comparator, AND is a logic AND gate, SPST is a single-pole single-throw switch, DAC is a digital-to-analog converter, Peak Hold Circuit is a peak holding circuit, and Up / Down potentiometer is a digital potentiometer, wherein the single-pole single-throw switch SPST is connected in series at the output end of the current source VCCS, and when it is disconnected, the current signal output by the current source VCCS to the human body can be cut off, so that overcurrent protection of the injected current to the human body can be realized.

[0044] Please refer to Figure 2 , the sampling circuit comprises a sampling resistor, an instrument amplifier and an operational amplifier;

[0045] Among them, Instrument amplifier is an instrument amplifier, Rshunt is a sampling resistor, amplifier is an operational amplifier, and the sampling resistor Rshunt is a Shunt Resistor in Figure 1 , which is connected to the output end of the current source, and can obtain the current signal output by the current source. The two input ends of the instrument amplifier Instrument amplifier are connected to the two ends of the sampling resistor Rshunt, and the instrument amplifier is a device capable of amplifying small signals in a noisy environment, which has a series of advantages such as low drift, low power consumption, high common-mode rejection ratio, wide power supply range and small size. It utilizes the characteristics that the differential small signal is superimposed on the larger common-mode signal, can remove the common-mode signal, and amplify the differential signal at the same time. The instrument amplifier Instrument amplifier in the application can convert the current signal at the two ends of the sampling resistor Rshunt into a voltage signal, and output the voltage signal to the operational amplifier amplifier at the same time. The operational amplifier amplifier is a multi-stage coupled amplifier with high voltage gain, high input resistance and low output resistance, which can amplify the voltage signal output by the instrument amplifier Instrument amplifier to meet the normal working voltage range of the subsequent comparator.

[0046] Please refer to Figure 3 The current peak holding circuit comprises a first comparator, a logic AND gate and a digital potentiometer.

[0047] Among them, Comparator is a first comparator, which corresponds to Figure 1 one Comparator on the left side, AND is a logic AND gate, and PTM is a digital potentiometer, which corresponds to Figure 1Up / Down potentiometer in the figure, wherein the inverting input terminal of the first comparator Comparator is connected to the output terminal of the sampling circuit, i.e. the output terminal of the operational amplifier amplifier, the non-inverting input terminal is connected to the output terminal of the digital potentiometer PTM, for obtaining the output signal of the digital potentiometer PTM, the first comparator Comparator is connected to the first input terminal of the logic AND gate AND, the second input terminal of the logic AND gate AND is connected to the master control unit MCU, and the output terminal is connected to the CS pin of the digital potentiometer PTM, and the U / D pin of the digital potentiometer PTM is connected to the master control unit.

[0048] Please refer to Figure 4 , which is the working mode diagram of the digital potentiometer PTM, wherein H indicates high level, and L indicates low level; when the CS pin is at low level and the U / D pin is at high level, the voltage signal output by the digital potentiometer PTM is raised;

[0049] When the CS pin and the U / D pin of the digital potentiometer PTM are both at low level, the voltage signal output by the digital potentiometer PTM is lowered;

[0050] When the CS pin of the digital potentiometer PTM is at high level, the voltage signal output by the digital potentiometer PTM is in a holding state.

[0051] Among them, the digital potentiometer PTM includes at least two working modes, which are reset mode and peak holding mode; when the digital potentiometer PTM is in the reset mode, it is used to clear the voltage stored in the digital potentiometer PTM to ensure normal detection when the current source is powered on;

[0052] When the digital potentiometer PTM is in the peak holding mode, it can raise the output of the digital potentiometer PTM and maintain it unchanged when the peak voltage is reached, and the peak voltage corresponds to the peak current, i.e. the peak current can be maintained unchanged.

[0053] When the digital potentiometer PTM works in the reset mode, the master control unit MCU sends a low level signal to the U / D pin;

[0054] When the digital potentiometer PTM works in the peak holding mode, the master control unit MCU sends a high level signal to the U / D pin.

[0055] Specifically, the working principle of the peak holding circuit is that when the peak holding circuit needs to realize the holding of the current peak, the main control unit MCU sends a high level signal to the U / D pin, that is, the control Reset signal is high, and the level of REF1 (that is, the output Vout of the digital potentiometer at the beginning) is 0. With the injection of current, as long as the Vin signal at the inverting input end is greater than 0V, the output of the comparator will be inverted, and the output is low. At this time, the CS output to the digital potentiometer PTM through the logic AND gate is low, and the U / D pin of the digital potentiometer PTM is high due to the connection with the main control unit. The Vout signal output by the digital potentiometer will increase with the increase of the input signal Vin. When the input signal Vin reaches the peak, the output signal Vout also reaches the maximum value, and REF1, that is, Vout, corresponds to the peak of Vin at the first comparator. When Vin decreases and is less than REF1, the voltage at the non-inverting input end is higher than that at the inverting input end, the comparator flips, and the output signal is high. At this time, the first input and the second input of the logic AND gate input high level signals, so the signal of the CS pin output to the digital potentiometer PTM is a high level signal, so the digital potentiometer PTM is in a holding state, the output is unchanged, and the output to the current source VCCS is also unchanged, in the current peak holding mode;

[0056] In addition, when the peak holding circuit is working, it is necessary to ensure that the initial output signal of the digital potentiometer is zero, so as to realize the reset of the digital potentiometer PTM. Specifically, when it is necessary to make the digital potentiometer PTM work in the reset mode, the main control unit MCU sends a low level signal to the digital potentiometer PTM. At this time, the U / D pin of the digital potentiometer is a low level signal, and the CS pin is also a low level signal. Therefore, the output voltage of the digital potentiometer PTM starts to decrease until the voltage signal output by the digital potentiometer PTM is zero.

[0057] Further, please refer to Figure 5 , the overcurrent protection circuit comprises: a digital-to-analog converter, a second comparator;

[0058] Among them, Comparator is the second comparator, which corresponds Figure 1 to the right Comparator, the non-inverting input end is connected to the main control unit MCU after the digital-to-analog converter DAC is connected in series, and the inverting input end is connected to the output end of the peak holding circuit. STPST is a switch unit, which corresponds Figure 1 to the single-pole single-throw switch SPST in , and the output signal of the second comparator Comparator is used as an enable signal for controlling the on-off state of the switch unit.

[0059] When the second comparator outputs a high level signal, the switch unit is closed;

[0060] When the second comparator outputs a low level signal, the switch unit is disconnected.

[0061] Specifically, the main control unit MCU configures the current peak threshold injected into the human body through the SPI bus, that is, sets the current safety threshold REF2 injected into the human body. The second reference voltage REF2 is output to the second comparator through the digital-to-analog converter DAC, and the voltage signal Vout output by the current peak holding circuit is compared with the threshold value REF2 set by the MCU in the second comparator. When Vout is higher than the second reference voltage REF2, the second comparator outputs a low level signal, so that the single-pole single-throw switch SPST is disconnected. Since the voltage signal output by the digital potentiometer PTM corresponds to the current signal output by the current source, when the voltage signal output by the digital potentiometer PTM exceeds the second reference voltage REF2, it means that the current signal output by the current source exceeds the threshold current.

[0062] Among them, the threshold current is set as the threshold value of the current source inputting the human body current. Through the setting of the sampling circuit, the voltage signal corresponding to the current threshold value can be determined, and the voltage signal is taken as the second reference voltage by the main control unit. Therefore, when the voltage signal output by the digital potentiometer is higher than the second reference voltage, it means that the current inputted into the human body by the current source exceeds the threshold value.

[0063] The application also provides an EIT device with the current peak injection control circuit.

[0064] Compared with the prior art, the application can realize the detection and retention of the current peak injected into the human body, improve the work efficiency, and at the same time, when the current inputted into the human body by the current source exceeds the threshold value, the current source can be disconnected to avoid the risk of electric shock to the human body.

[0065] The above only describes the preferred embodiments of the application and should not be used to limit the application. Any modification, equivalent replacement and improvement within the spirit and principle of the application should be included in the protection scope of the application.

Claims

1. A control circuit for the peak value of the injected current, characterized in that, include: A sampling circuit is connected to the output terminal of the current source to collect the current signal output by the current source and convert it into a voltage signal; A current peak hold circuit is connected to the output of the sampling circuit and can keep the current signal output by the current source at the current peak. An overcurrent protection circuit includes a switching unit connected in series with the output terminal of the current source, and can disconnect the switching unit when the current signal output by the current source is higher than a threshold current. A main control unit is connected to the current peak holding circuit and the overcurrent protection circuit respectively, and is used to control the working state of the current peak holding circuit and the overcurrent protection circuit. The current peak hold circuit includes: a first comparator, a logic AND gate, and a digital potentiometer; The inverting input of the first comparator is connected to the output of the sampling circuit, and the non-inverting input is connected to the output of the digital potentiometer. The output of the first comparator is connected to the first input of the AND gate. The second input of the AND gate is connected to the main control unit, and its output is connected to the CS pin of the digital potentiometer. The U / D pin of the digital potentiometer is connected to the main control unit.

2. The control circuit according to claim 1, characterized in that, The sampling circuit includes: a sampling resistor, an instrumentation amplifier, and an operational amplifier; The sampling resistor is connected in series with the output terminal of the current source. The input terminal of the instrumentation amplifier is connected to both ends of the sampling resistor, and the output terminal is connected to the input terminal of the operational amplifier. The output terminal of the operational amplifier is connected to the current peak holding circuit as the output terminal of the sampling circuit.

3. The control circuit according to claim 1, characterized in that, When the CS pin of the digital potentiometer is at a low level and the U / D pin is at a high level, the voltage signal output by the digital potentiometer increases. When both the CS pin and the U / D pin of the digital potentiometer are at a low level, the digital potentiometer... The voltage signal output by the bit positioner decreases; When the CS pin of the digital potentiometer is at a high level, the voltage signal output by the digital potentiometer is held.

4. The control circuit according to claim 3, characterized in that, When the digital potentiometer is in reset mode, the main control unit sends a low-level signal to the U / D pin; When the digital potentiometer is operating in peak hold mode, the main control unit sends a high-level signal to the U / D pin.

5. The control circuit according to claim 1, characterized in that, The overcurrent protection circuit also includes: a digital-to-analog converter and a second comparator; The input terminal of the digital-to-analog converter is connected to the main control unit, and the output terminal is connected to the non-inverting input terminal of the second comparator. The inverting input terminal of the second comparator is connected to the output terminal of the current peak hold circuit. The output signal of the second comparator serves as an enable signal for controlling the on / off state of the switching unit.

6. The control circuit according to claim 5, characterized in that, When the second comparator outputs a high-level signal, the switching unit is closed; When the second comparator outputs a low-level signal, the switching unit is turned off.

7. The control circuit according to claim 1, characterized in that, The threshold current is the threshold value for the current injected into the human body by the current source.

8. The control circuit according to claim 1, characterized in that, The switching unit is a single-pole single-throw switch.

9. EIT equipment, characterized in that, The EIT device has a control circuit as described in any one of claims 1 to 8.

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