CN107314799A - A kind of weak capacitive detection circuit for nanoliter level liquid level sensor - Google Patents
A kind of weak capacitive detection circuit for nanoliter level liquid level sensor Download PDFInfo
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Abstract
一种用于纳升级液位传感器的微弱电容检测电路，采用闭环模态局域化测量原理，第一振荡回路、第二振荡回路、耦合电容和反相放大电路输入连接，反相放大电路输出通过反馈回路和带通滤波器输入相连，带通滤波器输出和第一振荡回路、第二振荡回路连接，当液位发生改变时，导致输出电容发生变化，变化的电容ΔC并联在振荡回路的电容两端；第一振荡回路连接有第三缓冲器，第二振荡回路连接有第三缓冲器，第一振荡回路、第二振荡回路、耦合电容公共端连接有第一缓冲器，振荡回路不需要外接变频的交流驱动电压信号，只需给各个放大器提供直流工作电压；本发明实现在线实时监测电容变化，能够方便、快速、精确的读出电容式液位传感器微弱电容的变化情况。
A weak capacitance detection circuit for nanoliter liquid level sensors, using the principle of closed-loop modal localization measurement, the first oscillating loop, the second oscillating loop, the coupling capacitance and the input connection of the inverting amplifier circuit, and the output of the inverting amplifier circuit The feedback loop is connected to the input of the band-pass filter, and the output of the band-pass filter is connected to the first oscillating circuit and the second oscillating circuit. When the liquid level changes, the output capacitance changes, and the changed capacitance ΔC is connected in parallel to the oscillating circuit. Both ends of the capacitor; the first oscillating circuit is connected to the third buffer, the second oscillating circuit is connected to the third buffer, the first oscillating circuit, the second oscillating circuit, and the common end of the coupling capacitor are connected to the first buffer, and the oscillating circuit is not The AC driving voltage signal with frequency conversion needs to be externally connected, and only the DC operating voltage needs to be provided to each amplifier; the invention realizes online real-time monitoring of capacitance changes, and can read the changes of the weak capacitance of the capacitive liquid level sensor conveniently, quickly and accurately.
Description
技术领域technical field
本发明涉及液位传感器技术领域，特别涉及一种用于纳升级液位传感器的微弱电容检测电路。The invention relates to the technical field of liquid level sensors, in particular to a weak capacitance detection circuit for nanoliter liquid level sensors.
背景技术Background technique
MEMS电容式传感器具有环境适应性好，灵敏度高的特点，在工业领域被广泛应用。基于MEMS技术的连续液位测量和液位信号器的出现，可以实现μm(10-6m)/nL(10-9L)级别液位测量，同时电容式液位传感器具有较好的环境适应性和温度稳定性等特点，可以填补常规工艺下的液位传感器应用领域的空白，被广泛地应用于石油化工、生物制药微型流量控制等领域，并向高精度，小体积，大量程范围发展。MEMS capacitive sensors have the characteristics of good environmental adaptability and high sensitivity, and are widely used in industrial fields. Continuous liquid level measurement based on MEMS technology and the appearance of liquid level signal can realize μm (10 -6 m)/nL (10 -9 L) level liquid level measurement, and capacitive liquid level sensor has better environmental adaptability It can fill the gap in the application field of liquid level sensors under conventional processes, and is widely used in petrochemical, biopharmaceutical micro-flow control and other fields, and is developing towards high precision, small volume, and large range. .
电容式MEMS液位传感器采用MEMS(微机电系统)加工工艺，其将液位信号转化为电信号，可以等效成一个随液位变化的待测电容，电容变化区间在1-200pF(10-12F)之间。对于10pF以下的电容，由于PCB电路板所产生的寄生电容已达到这个量级，很难使用传统的方法测量，急需提出新的测试方法来解决。现有木代雅巳、金湘亮等人采用的PCB级别电容读取电路，前者需要采用PCB电路焊接虚设电容的方式，难以克服电容选择误差，而后者通过相关双采样技术消除了失调电压，同时集成了数模转换器，杂散电容补偿阵列，以抵消静态偏移的影响，但是存在量化误差以及电路设计过于复杂的情况，可能导致逐级噪声累加。The capacitive MEMS liquid level sensor adopts MEMS (micro-electromechanical system) processing technology, which converts the liquid level signal into an electrical signal, which can be equivalent to a measured capacitance that changes with the liquid level, and the capacitance variation range is 1-200pF (10 - 12 F). For the capacitance below 10pF, since the parasitic capacitance generated by the PCB circuit board has reached this level, it is difficult to use the traditional method to measure, and it is urgent to propose a new test method to solve it. The current PCB-level capacitance reading circuit used by Masami Kishiro, Xiangliang Jin, etc., the former needs to use the method of soldering dummy capacitors on the PCB circuit, which is difficult to overcome the capacitance selection error, while the latter eliminates the offset voltage through correlated double sampling technology, and integrates Digital-to-analog converters, stray capacitance compensation arrays to counteract the effects of static offsets, but there are quantization errors and overly complex circuit designs that may lead to stage-by-stage noise accumulation.
一种低g值电容式MEMS加速度计及其模态局域化测量电路首次提出模态局域化与高灵敏度差分加计结合的方法，为电容检测技术打开了新思路。该方法使用两个等效LRC振荡环路，通过耦合电容耦合的起来，将MEMS加速度计的电容变化转化为模态局域化电路的电流变化，电路两个环路的响应电流与电容变化近似呈线性变化关系。然而这种方式需要一个额外的信号发生器进行扫频操作，并且需实时记录下频率-电流信号，才能进行离线计算，不能实时得到信号结果，且稳定性不佳，可能发生频率漂移过大的情况，这种开环方式在实际应用中还存在许多问题。A low-g value capacitive MEMS accelerometer and its modal localization measurement circuit proposed the method of combining modal localization and high-sensitivity differential accelerometer for the first time, which opened up new ideas for capacitance detection technology. This method uses two equivalent LRC oscillation loops, which are coupled by coupling capacitors, and converts the capacitance change of the MEMS accelerometer into the current change of the modal localization circuit. The response current of the two loops of the circuit is similar to the capacitance change There is a linear variation relationship. However, this method requires an additional signal generator for frequency sweep operation, and needs to record the frequency-current signal in real time before performing offline calculations. The signal result cannot be obtained in real time, and the stability is not good, and the frequency drift may be too large. However, there are still many problems in this open-loop approach in practical applications.
发明内容Contents of the invention
为了克服上述现有技术的缺点，本发明的目的是提出一种闭环模态局域化测量电路方法，用于纳升级液位传感器的微弱电容检测，方便、快速的读出电容式液位传感器微弱电容的变化情况。In order to overcome the shortcomings of the above-mentioned prior art, the object of the present invention is to propose a closed-loop modal localization measurement circuit method for weak capacitance detection of nanoliter liquid level sensors, and convenient and fast readout of capacitive liquid level sensors Changes in the weak capacitance.
为达到上述目的，本发明采取的技术方案是：For achieving the above object, the technical scheme that the present invention takes is:
一种用于纳升级液位传感器的微弱电容检测电路，采用闭环模态局域化测量原理，包括电容C3、C4，电容C3、C4串联连接后，与依次串联的电阻R1、电感L1、电容C1并联，同时与依次串联的电阻R2、电感L2、电容C2并联，其中电容C4右端与电容C1、电容C2右端相连，电容C3左端与电阻R1、电阻R2左端相连，电容C3、C4串联构成耦合电容6；电阻R1、电感L1、电容C1与串联的电容C3、C4构成第一振荡回路1，电阻R2、电容C2和电感L2与串联的电容C3、C4构成第二振荡回路2；电容C3、C4公共端共地，第一振荡回路1、第二振荡回路2中电容C1、C2、C4的右端通过电阻R3输入到第一放大器(Op-amp)反相输入端，第一放大器反相输入端和电阻R4一端相连，电阻R4另一端和第一放大器输出端相连，第一放大器同相输入端接地，电阻R3、R4和第一放大器构成反相放大电路3；反相放大电路3输出端通过反馈回路4和带通滤波器5输入端相连，带通滤波器5输出端和分压电阻R5一端连接，分压电阻R5另一端和电阻R1、电阻R2左端连接；A weak capacitance detection circuit for nanoliter liquid level sensors, which adopts the principle of closed-loop modal localization measurement, including capacitors C 3 and C 4 . After capacitors C 3 and C 4 are connected in series, they are connected in series with resistor R 1 , inductor L 1 , and capacitor C 1 are connected in parallel, and at the same time, they are connected in parallel with resistor R 2 , inductor L 2 , and capacitor C 2 that are serially connected in series, wherein the right end of capacitor C 4 is connected to the right end of capacitor C 1 and capacitor C 2 , and the left end of capacitor C 3 is connected to the resistor R 1 and resistor R 2 are connected to the left, capacitors C 3 and C 4 are connected in series to form coupling capacitor 6; resistor R 1 , inductor L 1 , capacitor C 1 and capacitors C 3 and C 4 connected in series form the first oscillation circuit 1, and resistor R 2. Capacitor C 2 , inductance L 2 and capacitors C 3 and C 4 connected in series constitute the second oscillating circuit 2; the common terminals of capacitors C 3 and C 4 share the ground, and the capacitance C in the first oscillating circuit 1 and the second oscillating circuit 2 1. The right ends of C 2 and C 4 are input to the inverting input terminal of the first amplifier (Op-amp) through the resistor R 3 , the inverting input terminal of the first amplifier is connected to one end of the resistor R 4 , and the other end of the resistor R 4 is connected to the first The output terminals of the amplifiers are connected, the non-inverting input terminal of the first amplifier is grounded, and the resistors R3 , R4 and the first amplifier constitute an inverting amplifier circuit 3 ; the output terminal of the inverting amplifier circuit 3 is connected to the input terminal of the bandpass filter 5 through a feedback loop 4 , the output end of the bandpass filter 5 is connected to one end of the voltage dividing resistor R5, and the other end of the voltage dividing resistor R5 is connected to the left end of the resistor R1 and the resistor R2 ;
当液位改变时，导致输出电容发生变化，变化的电容ΔC并联在电容C2两端；When the liquid level changes, the output capacitance changes, and the changed capacitance ΔC is connected in parallel at both ends of the capacitance C2;
电容C3、电阻R1、电阻R2左端连接有第一缓冲器7，电阻R1和电感L1之间连接有第三缓冲器9，电阻R2和电感L2之间连接有第二缓冲器8。The first buffer 7 is connected to the left end of the capacitor C 3 , the resistor R 1 , and the resistor R 2 , the third buffer 9 is connected between the resistor R 1 and the inductor L 1 , and the second buffer 9 is connected between the resistor R 2 and the inductor L 2 Buffer 8.
第三缓冲器9、第二缓冲器8输出端分别接入单刀双掷开关S12的a、b节点，S12的固定端与电阻R9一端连接，电阻R9另一端接入第二放大器反相输入端，第二放大器反相输入端和电阻R10一端相连，电阻R10另一端和第二放大器输出端相连，第二放大器同相输入端和电阻R12一端相连，电阻R12另一端接地；第一缓冲器7输出端和电阻R11一端相连，电阻R11另一端与第二放大器反相输入端相连；第二放大器输出端与电阻R13一端相连，电阻R13另一端和第四放大器反相输入端连接，第四放大器反相输入端和电阻R14一端相连，电阻R14另一端和第四放大器输出端相连，第四放大器同相输入端与电阻R15一端相连，电阻R15另一端接地。The output ends of the third buffer 9 and the second buffer 8 are respectively connected to nodes a and b of the SPDT switch S12 , the fixed end of S12 is connected to one end of the resistor R9 , and the other end of the resistor R9 is connected to the second amplifier inverter phase input terminal, the inverting input terminal of the second amplifier is connected to one end of the resistor R 10 , the other end of the resistor R 10 is connected to the output terminal of the second amplifier, the non-inverting input terminal of the second amplifier is connected to one end of the resistor R 12 , and the other end of the resistor R 12 is grounded ; The output terminal of the first buffer 7 is connected to one end of the resistor R 11 , and the other end of the resistor R 11 is connected to the inverting input terminal of the second amplifier; the output terminal of the second amplifier is connected to one end of the resistor R 13 , and the other end of the resistor R 13 is connected to the fourth The inverting input terminal of the amplifier is connected, the inverting input terminal of the fourth amplifier is connected to one end of the resistor R 14 , the other end of the resistor R 14 is connected to the output terminal of the fourth amplifier, the non-inverting input terminal of the fourth amplifier is connected to one end of the resistor R 15 , and the resistor R 15 The other end is grounded.
所述的第一缓冲器7、第二缓冲器8、第三缓冲器9采用相同的结构，即信号点与第五放大器反相输入端相连，第五放大器反相输入端和输出端短接。The first buffer 7, the second buffer 8, and the third buffer 9 adopt the same structure, that is, the signal point is connected to the inverting input terminal of the fifth amplifier, and the inverting input terminal and the output terminal of the fifth amplifier are short-circuited .
所述的带通滤波器5信号输入端in与电阻R6一端相连，电阻R6另一端与电容C5相连，电容C5另一端与第六放大器反相输入端相连，第六放大器同相输入端接地，第六放大器反相输入端与电阻R8一端相连，电阻R8另一端与第六放大器输出端接通，第六放大器输出端和电容C6一端连接，电容C6另一端与电阻R6、电容C5公共端相连，电阻R6、电容C5公共端与电阻R7一端相连，电阻R7另一端与第六放大器同相输入端共地。The signal input terminal in of the band-pass filter 5 is connected to one end of the resistor R6, the other end of the resistor R6 is connected to the capacitor C5 , the other end of the capacitor C5 is connected to the inverting input terminal of the sixth amplifier, and the non-inverting input terminal of the sixth amplifier The terminal is grounded, the inverting input terminal of the sixth amplifier is connected to one end of the resistor R8 , the other end of the resistor R8 is connected to the output terminal of the sixth amplifier, the output terminal of the sixth amplifier is connected to one end of the capacitor C6 , and the other end of the capacitor C6 is connected to the resistor The common end of R 6 and capacitor C 5 is connected, the common end of resistor R 6 and capacitor C 5 is connected to one end of resistor R 7 , and the other end of resistor R 7 shares the ground with the non-inverting input end of the sixth amplifier.
与现有技术相比，本发明至少具有以下有益效果：在本发明中，系统振荡回路不需要外接变频的交流电压驱动信号，只需给各个放大器提供直流工作电压；通过形成闭环回路，可实现在线实时监测输入变化电容情况，极大地提升了电容检测的可行性与实时性。Compared with the prior art, the present invention has at least the following beneficial effects: In the present invention, the system oscillation circuit does not need an external frequency-variable AC voltage drive signal, and only needs to provide DC operating voltage to each amplifier; by forming a closed loop, it can realize Online real-time monitoring of input capacitance changes greatly improves the feasibility and real-time performance of capacitance detection.
附图说明Description of drawings
图1是本发明闭环模态局域化电路原理图。Fig. 1 is a schematic diagram of the closed-loop modal localization circuit of the present invention.
图2是本发明信号处理电路原理图。Fig. 2 is a schematic diagram of the signal processing circuit of the present invention.
图3是缓冲器的结构示意图。Fig. 3 is a schematic diagram of the structure of the buffer.
图4是带通滤波单元的结构示意图。Fig. 4 is a schematic structural diagram of a band-pass filtering unit.
图5是模态局域化开环检测原理图。Fig. 5 is a schematic diagram of mode localization open-loop detection.
图6是本发明信号处理的流程图。Fig. 6 is a flowchart of the signal processing of the present invention.
图7是实施例测得一组数据。Fig. 7 is a set of data measured by the embodiment.
具体实施方式detailed description
下面结合附图和实施例对本发明作详细描述。The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.
如图1所示，一种用于纳升级液位传感器的微弱电容检测电路，采用闭环模态局域化测量原理，包括电容C3、C4，电容C3、C4串联连接后，与依次串联的电阻R1、电感L1、电容C1并联，同时与依次串联的电阻R2、电感L2、电容C2并联，其中电容C4右端与电容C1、电容C2右端相连，电容C3左端与电阻R1、电阻R2左端相连，电容C3、C4串联构成耦合电容6；电阻R1、电感L1、电容C1与串联的电容C3、C4构成第一振荡回路1，电阻R2、电容C2和电感L2与串联的电容C3、C4构成第二振荡回路2；电容C3、C4公共端共地，第一振荡回路1、第二振荡回路2中电容C1、C2、C4的右端通过电阻R3输入到第一放大器(Op-amp)反相输入端，第一放大器反相输入端和电阻R4一端相连，电阻R4另一端和第一放大器输出端相连，第一放大器同相输入端接地，电阻R3、R4和第一放大器构成反相放大电路3；反相放大电路3输出端通过反馈回路4和带通滤波器5输入端相连，带通滤波器5输出端和分压电阻R5一端连接，分压电阻R5另一端和电阻R1、电阻R2左端连接；As shown in Figure 1, a weak capacitance detection circuit for nanoliter liquid level sensors adopts the principle of closed-loop modal localization measurement, including capacitors C 3 and C 4 . After capacitors C 3 and C 4 are connected in series, they are connected with Resistor R 1 , inductor L 1 , and capacitor C 1 are connected in parallel in series, and connected in parallel with resistor R 2 , inductor L 2 , and capacitor C 2 in series in sequence, where the right end of capacitor C 4 is connected to the right end of capacitor C 1 and capacitor C 2 , The left end of capacitor C 3 is connected to the left end of resistor R 1 and resistor R 2 , capacitors C 3 and C 4 are connected in series to form coupling capacitor 6; resistor R 1 , inductor L 1 , capacitor C 1 and capacitors C 3 and C 4 connected in series form the first Oscillating circuit 1, resistor R 2 , capacitor C 2 , inductance L 2 and capacitors C 3 and C 4 connected in series constitute the second oscillating circuit 2; the common terminals of capacitors C 3 and C 4 share the ground, the first oscillating circuit 1 and the second The right ends of the capacitors C 1 , C 2 , and C 4 in the oscillation circuit 2 are input to the inverting input terminal of the first amplifier (Op-amp) through the resistor R 3 , the inverting input terminal of the first amplifier is connected to one end of the resistor R 4 , and the resistor R The other end of 4 is connected to the output terminal of the first amplifier, the non-inverting input terminal of the first amplifier is grounded, and the resistors R3 , R4 and the first amplifier form an inverting amplifier circuit 3 ; the output terminal of the inverting amplifier circuit 3 passes through the feedback loop 4 and the bandpass The input terminal of the filter 5 is connected, the output terminal of the bandpass filter 5 is connected to one end of the voltage dividing resistor R5, and the other end of the voltage dividing resistor R5 is connected to the left end of the resistor R1 and the resistor R2 ;
当液位改变时，导致输出电容发生变化，变化的电容ΔC并联在电容C2两端；When the liquid level changes, the output capacitance changes, and the changed capacitance ΔC is connected in parallel at both ends of the capacitance C2;
电容C3、电阻R1、电阻R2左端连接有第一缓冲器7，电阻R1和电感L1之间连接有第三缓冲器9，电阻R2和电感L2之间连接有第二缓冲器8。The first buffer 7 is connected to the left end of the capacitor C 3 , the resistor R 1 , and the resistor R 2 , the third buffer 9 is connected between the resistor R 1 and the inductor L 1 , and the second buffer 9 is connected between the resistor R 2 and the inductor L 2 Buffer 8.
变化的电容ΔC输入到电容C2两端，第一振荡回路1，第二振荡回路2的平衡状态被引入的变化电容ΔC打破，引起模态局域化现象，导致相应的振荡电流i1、i2、发生变化；第一、第二振荡回路通过串联的耦合电容C3、C4形成弱耦合，信号从C4右端输入到反相放大器3，经放大后进入带通滤波器5去除纹波噪声，经电阻R5分压后反馈输入到电阻R1左端；耦合电容C3、C4同时还起到调节反馈强度的作用，其比例作为调节参数，可使电路稳定高效的振荡起来。The changing capacitance ΔC is input to both ends of the capacitor C 2 , the balance state of the first oscillation circuit 1 and the second oscillation circuit 2 is broken by the introduced changing capacitance ΔC, causing the mode localization phenomenon, resulting in the corresponding oscillation current i 1 , i 2 , changes; the first and second oscillating circuits form weak coupling through the series coupling capacitors C 3 and C 4 , the signal is input from the right end of C 4 to the inverting amplifier 3, and after being amplified, enters the band-pass filter 5 to remove the ripple Wave noise, the feedback is input to the left end of resistor R1 after the resistor R5 divides the voltage ; the coupling capacitors C3 and C4 also play the role of adjusting the feedback intensity, and their ratio As an adjustment parameter, it can make the circuit oscillate stably and efficiently.
参照图2，第三缓冲器9、第二缓冲器8输出端分别接入单刀双掷开关S12的a、b节点，S12的固定端与电阻R9一端连接，电阻R9另一端接入第二放大器反相输入端，第二放大器反相输入端和电阻R10一端相连，电阻R10另一端和第二放大器输出端相连，第二放大器同相输入端和电阻R12一端相连，电阻R12另一端接地；第一缓冲器7输出端和电阻R11一端相连，电阻R11另一端与第二放大器反相输入端相连；第二放大器输出端与电阻R13一端相连，电阻R13另一端和第四放大器反相输入端连接，第四放大器反相输入端和电阻R14一端相连，电阻R14另一端和第四放大器输出端相连，第四放大器同相输入端与电阻R15一端相连，电阻R15另一端接地。Referring to Fig. 2, the output ends of the third buffer 9 and the second buffer 8 are respectively connected to nodes a and b of the SPDT switch S12 , the fixed end of S12 is connected to one end of the resistor R9 , and the other end of the resistor R9 is connected to The inverting input terminal of the second amplifier, the inverting input terminal of the second amplifier is connected to one end of the resistor R 10 , the other end of the resistor R 10 is connected to the output terminal of the second amplifier, the non-inverting input terminal of the second amplifier is connected to one end of the resistor R 12 , and the resistor R 12 , the other end is grounded; the output end of the first buffer 7 is connected to one end of the resistor R 11 , and the other end of the resistor R 11 is connected to the inverting input end of the second amplifier; the output end of the second amplifier is connected to one end of the resistor R 13 , and the other end of the resistor R 13 One end is connected to the inverting input end of the fourth amplifier, the inverting input end of the fourth amplifier is connected to one end of the resistor R 14 , the other end of the resistor R 14 is connected to the output end of the fourth amplifier, and the non-inverting input end of the fourth amplifier is connected to one end of the resistor R 15 , the other end of the resistor R 15 is grounded.
第一缓冲器7、第二缓冲器8、第三缓冲器9分别将检测的相应的信号点参数通过差分放大计算，其中单刀双掷开关S12按照测量时序，分被接通a点和b点，与第一缓冲器7输入的信号做差分运算；其中当第三缓冲器9接通时，监测到的信号与第一振荡回路i1相关；其中当第二缓冲器8接通时，监测到的信号与第二振荡回路i2相关；信号进入第四放大器，经反相放大后输出到DSP中作进一步运算。The first buffer 7, the second buffer 8, and the third buffer 9 respectively calculate the corresponding detected signal point parameters through differential amplification, wherein the single-pole double-throw switch S 12 is turned on points a and b according to the measurement timing. Point, do differential operation with the signal input by the first buffer 7; wherein when the third buffer 9 is connected, the monitored signal is related to the first oscillation circuit i1; wherein when the second buffer 8 is connected, The monitored signal is related to the second oscillating circuit i2 ; the signal enters the fourth amplifier, and is output to the DSP for further calculation after inverting and amplifying.
通过第一缓冲器7、第二缓冲器8、第三缓冲器9采样得到3点电压信号V7、V8、V9做差分放大处理，即得到电阻R1、R2上的电流值：Through the sampling of the first buffer 7, the second buffer 8, and the third buffer 9, the three-point voltage signals V 7 , V 8 , and V 9 are obtained for differential amplification processing, that is, the current values on the resistors R 1 and R 2 are obtained:
其中K为第四放大器的放大倍数。Where K is the amplification factor of the fourth amplifier.
参照图3，所述的第一缓冲器7、第二缓冲器8、第三缓冲器9采用相同的结构，即信号点与第五放大器反相输入端相连，第五放大器反相输入端和输出端短接。With reference to Fig. 3, described first buffer 7, second buffer 8, the 3rd buffer 9 adopt identical structure, promptly signal point is connected with the fifth amplifier inverting input end, the fifth amplifier inverting input end and The output is shorted.
缓冲器由一个运算放大器构成，信号通过同相输入端进入，输入端即可得到衰减较小的电压信号；第五放大器输出端和反相输入端短接，理论输出阻抗无限大，可以尽可能小的减小对振荡回路的影响。The buffer is composed of an operational amplifier, the signal enters through the non-inverting input terminal, and the input terminal can get a voltage signal with less attenuation; the output terminal of the fifth amplifier is shorted to the inverting input terminal, and the theoretical output impedance is infinite, which can be as small as possible The reduction of the impact on the oscillation circuit.
参照图4，所述的带通滤波器5信号输入端与电阻R6一端相连，电阻R6另一端与电容C5相连，电容C5另一端与第六放大器反相输入端相连，第六放大器同相输入端接地，第六放大器反相输入端与电阻R8一端相连，电阻R8另一端与第六放大器输出端接通，第六放大器输出端和电容C6一端连接，电容C6另一端与电阻R6、电容C5公共端相连，电阻R6、电容C5公共端与电阻R7一端相连，电阻R7另一端与第六放大器同相输入端共地。Referring to Fig. 4, the signal input terminal of the bandpass filter 5 is connected with one end of the resistor R6, the other end of the resistor R6 is connected with the capacitor C5 , and the other end of the capacitor C5 is connected with the inverting input terminal of the sixth amplifier, the sixth amplifier The non-inverting input terminal of the amplifier is grounded, the inverting input terminal of the sixth amplifier is connected to one end of the resistor R8 , the other end of the resistor R8 is connected to the output terminal of the sixth amplifier, the output terminal of the sixth amplifier is connected to one end of the capacitor C6 , and the other end of the capacitor C6 One end is connected to the common end of the resistor R 6 and the capacitor C 5 , the common end of the resistor R 6 and the capacitor C 5 is connected to one end of the resistor R 7 , and the other end of the resistor R 7 shares the ground with the non-inverting input end of the sixth amplifier.
根据预设的中心频率fp计算公式设置带通滤波参数，得以下方程：Set the band-pass filter parameters according to the preset center frequency f p calculation formula, and get the following equation:
其中C5＝C6＝C＝1nF,Bw为设计带宽，联立方程即可解得电阻R6、R7、R8的参数。Among them, C 5 =C 6 =C=1nF, B w is the design bandwidth, and the parameters of resistors R 6 , R 7 , and R 8 can be obtained by solving the simultaneous equations.
本发明的工作原理为：Working principle of the present invention is:
采用闭环模态局域化检测原理，通过输入电容变化引起上下环路振荡电流的改变，经放大、带通滤波环节后构成闭环回路；通过两支路电流信号作比较，可得到下支路电容变化量。Using the principle of closed-loop modal localization detection, the change of the upper and lower loop oscillating current is caused by the change of input capacitance, and the closed-loop loop is formed after amplification and band-pass filtering; the capacitance of the lower branch can be obtained by comparing the current signals of the two branches amount of change.
第一、第二振荡回路通过基尔霍夫电压定律可以得到微分方程：The differential equation of the first and second oscillation circuits can be obtained through Kirchhoff's voltage law:
上式中，L1＝L2＝L表示电路第一、第二环路的电感值，R1＝R1＝R表示ASIC电路上下环路的电阻值，CC表示两个环路之间耦合电容值(即电容C3、C4串联电容值)，C表示第一、第二振荡回路的参考电容值，q1，q2为电路两个回路i1,i2的积分，vs是反馈回路R5输入到第一振荡回路、第二振荡回路的能量，f为两个回路耦合后的振荡频率。由上式解得：In the above formula, L 1 ＝L 2 ＝L represents the inductance value of the first and second loops of the circuit, R 1 ＝R 1 ＝R represents the resistance value of the upper and lower loops of the ASIC circuit, C C represents the inductance value between the two loops Coupling capacitance value (that is, capacitance C 3 , C 4 series capacitance value), C represents the reference capacitance value of the first and second oscillation circuits, q 1 and q 2 are the integrals of the two circuits i 1 and i 2 of the circuit, v s is the energy input by the feedback loop R5 to the first oscillation loop and the second oscillation loop, and f is the oscillation frequency after the coupling of the two loops. Solved from the above formula:
其中wd1和wd2为模态局域化电路的谐振角频率，u(t)为模态局域化电路的特征向量。S代表经拉普拉斯变换后时域时间t对应的复频率，Q1和Q2分别对应q1、q2经过拉普拉斯变化后的值。Among them, w d1 and w d2 are the resonant angular frequencies of the mode localization circuit, and u(t) is the eigenvector of the mode localization circuit. S represents the complex frequency corresponding to the time t in the time domain after the Laplace transform, and Q 1 and Q 2 respectively correspond to the values of q 1 and q 2 after Laplace transform.
在谐振角频率wd1和wd2上，q1,q2取峰值，其值随ΔC变化而变化，wd1和wd2同样随着ΔC变化而改变，由此，可以通过计算得到wd1和wd2下的q1,q2对应的峰值，而q1，q2为ASIC电路两个回路i1,i2的积分，即可以得到谐振频率下i1,i2随着ΔC变化的关系，进而得到i1,i2与液位变化的关系。At the resonant angular frequencies w d1 and w d2 , q 1 and q 2 take peak values, and their values change with the change of ΔC, and w d1 and w d2 also change with the change of ΔC. Therefore, w d1 and q 2 can be obtained by calculation The peak values corresponding to q 1 and q 2 under w d2 , and q 1 and q 2 are the integrals of the two loops i 1 and i 2 of the ASIC circuit, that is, the relationship between i 1 and i 2 changing with ΔC at the resonance frequency can be obtained , and then get the relationship between i 1 , i 2 and the liquid level change.
如图5所示，图5是已有的开环模态局域化测量原理：两组耦合起来的RLC振荡回路10、RLC振荡回路11，通过耦合电容CC构成弱耦合，振荡回路通过外部交流源输入能量，需要使用相关设备实时记录下交流源信号变化下引起的振荡电流i1,i2变化情况，且需要离线标记谐振角频率wd1和wd2上峰值和频率，运算过程漫长，无法实时记录下信息。而本发明构建闭环控制回路以实现更加便捷、直观的读取方式。闭环系统将不需要交流源，通过闭环反馈电路，可以维持第一振荡回路、第二振荡回路在相应wd1和wd2的峰值电流上，实现快速采集、快速计算。As shown in Figure 5, Figure 5 is the existing open-loop modal localization measurement principle: two groups of coupled RLC oscillation circuits 10 and RLC oscillation circuits 11 form a weak coupling through the coupling capacitor C C , and the oscillation circuits pass through the external For AC source input energy, relevant equipment needs to be used to record in real time the changes of the oscillating current i 1 and i 2 caused by the change of the AC source signal, and the peak values and frequencies of the resonant angular frequencies w d1 and w d2 need to be marked off-line. The calculation process is long. Information cannot be recorded in real time. However, the present invention constructs a closed-loop control loop to realize a more convenient and intuitive reading method. The closed-loop system does not need an AC source. Through the closed-loop feedback circuit, the first oscillation loop and the second oscillation loop can be maintained at the corresponding peak currents of w d1 and w d2 to achieve fast acquisition and calculation.
如图6所示，本发明信号处理的流程如下：As shown in Figure 6, the flow process of the signal processing of the present invention is as follows:
1)系统复位清楚之前以后的数据；1) Reset the system to clear the previous and subsequent data;
2)预判液位传感器的电容变化范围；2) Predict the capacitance change range of the liquid level sensor;
3)选择第一振荡回路1、第二振荡回路2的C1、C2参数值，根据弱耦合设计原则，选定耦合电容C3、C4的值；选择带通滤波器参数，反相放大器接入DC电压起振；3) Select the C 1 and C 2 parameter values of the first oscillating circuit 1 and the second oscillating circuit 2, and select the values of the coupling capacitors C 3 and C 4 according to the weak coupling design principle; select the parameters of the bandpass filter, and invert The amplifier is connected to the DC voltage to start oscillation;
4)使用差分放大电路读取第一缓冲器7、第二缓冲器8、第三缓冲器9测得的信号，计算第一振荡回路1、第二振荡回路2的振荡电流峰值i1,i2；4) Use the differential amplifier circuit to read the signals measured by the first buffer 7, the second buffer 8, and the third buffer 9, and calculate the oscillation current peak values i 1 , i of the first oscillation circuit 1 and the second oscillation circuit 2 2 ;
5)将得到数据传入DSP中计算，输出电容值。5) Pass the obtained data into the DSP for calculation, and output the capacitance value.
实施例：设计参数C1＝100nF晦C2＝95nF晦L1＝L2＝10mH,设置带通滤波器C3＝100μF，C4＝20μF，中心频率5.4KHz，带宽1KHz，增益为1。设定ΔC/C1为输入扰动。设置当ΔC＝5nF时第一振荡回路1、第二振荡回路2所得电流为参考电流i10、i20，所得频率为参考频率f0。经过实验测量，将测得的电流信号和扩大100倍后的频率信号绘制如图7所示。得到该闭环模态局域化方法的检测灵敏度(电流曲线斜率)远高于传统的频率检测方法。Example: design parameters C 1 =100nF, C 2 =95nF, L 1 =L 2 =10mH, set bandpass filter C 3 =100μF, C 4 =20μF, center frequency 5.4KHz, bandwidth 1KHz, gain 1. Set ΔC/C 1 as the input disturbance. When ΔC=5nF, the current obtained by the first oscillating circuit 1 and the second oscillating circuit 2 is set as the reference current i 10 , i 20 , and the obtained frequency is the reference frequency f 0 . After experimental measurement, the measured current signal and the frequency signal enlarged by 100 times are plotted as shown in Figure 7. The detection sensitivity (slope of the current curve) of the closed-loop mode localization method is much higher than that of the traditional frequency detection method.
无扰动下测得基频f0＝5.4KHz，频率读取最小分辨率为1Hz，图7中频率斜率k＝0.013382Hz/nF，故而频率检测方式的最小电容分辨率为The measured fundamental frequency f 0 = 5.4KHz without disturbance, the minimum resolution of frequency reading is 1Hz, the frequency slope k in Figure 7 = 0.013382Hz/nF, so the minimum capacitance resolution of the frequency detection method is
而使用模态局域化电容检测方式的分辨率是频率方式的100倍以上，故而本发明所公开的模态局域化电容检测电路的最小分辨率至少为fF(10-15F)级别。The resolution of the modal localized capacitance detection method is more than 100 times that of the frequency method, so the minimum resolution of the modal localized capacitance detection circuit disclosed in the present invention is at least fF (10 −15 F) level.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109752046A (en) * | 2018-10-19 | 2019-05-14 | 江苏未来智慧信息科技有限公司 | Wireless vibration temperature sensor circuit |
| CN109752046B (en) * | 2018-10-19 | 2024-04-02 | 江苏未来智慧信息科技有限公司 | Wireless vibration temperature sensor circuit |
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