An excitation circuit for an electromagnetic conductivity sensor

Abstract

The present invention discloses an excitation circuit for an electromagnetic conductivity sensor. The excitation circuit includes: a square wave generating circuit, a frequency division circuit, a filtering circuit, and a driving circuit connected in sequence. The driving circuit is connected to the transmitting coil of the electromagnetic conductivity sensor; the square wave generating circuit is used to generate a quadruple-frequency square wave of a required sine wave and output it to the frequency division circuit; the frequency division circuit is used to divide the received quadruple-frequency square wave to obtain four quadruple-frequency divided square waves, and any one of them is output to the filtering circuit; the filtering circuit is used to filter one of the received quadruple-frequency divided square waves to obtain the required sine wave and output it to the driving circuit; the driving circuit is used to excite the transmitting coil according to the received sine wave. The present invention generates a sinusoidal alternating voltage through the method of square wave and low-pass filtering, and the generated sinusoidal alternating voltage excites the transmitting coil through the driving circuit, effectively reducing costs.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic conductivity sensors, and particularly to an excitation circuit for an electromagnetic conductivity sensor. Background Art

[0002] An electromagnetic conductivity sensor measures the conductivity of a solution through the principle of electromagnetic induction. Due to its wide measurement range and the electrodes being not easily contaminated and corroded by the liquid, it is usually applied in harsh medium environments such as measuring the concentration of acids, alkalis, and salts.

[0003] An electromagnetic conductivity sensor includes a transmitting coil and a receiving coil, which are usually specifically implemented as toroidal coils. The two coils are inserted into the medium to be measured, and the medium to be measured passes through the central hole of the coils, forming a closed current path. The transmitting coil generates an alternating magnetic field, which generates an induced current in the medium to be measured. The induced current in turn causes the receiving coil to generate an induced current related to the conductivity of the medium to be measured, and the conductivity of the measured medium is calculated through this current.

[0004] To make the transmitting coil generate an alternating magnetic field, an excitation circuit needs to apply an alternating voltage to the transmitting coil. Most of the alternating voltages in existing sensors are sine waves, and a DDS chip is usually used to generate sine waves. However, while DDS chips on the existing market have powerful functions, they have high costs and large volumes, and the powerful functions cannot be fully applied to the existing designs, resulting in waste. The update speed of existing semiconductor devices is too fast. In the design, there is an over-reliance on DDS chips with a high degree of integration. After the production of this chip stops, it is difficult to find a suitable chip again, and sometimes it is equivalent to redesigning the circuit. There are also cases where a single-chip microcomputer and a D / A are directly used to output a sine wave modulation signal, but outputting this signal occupies a large amount of single-chip microcomputer resources, resulting in the need for a higher-speed single-chip microcomputer in the product design, thereby increasing the device cost and the wiring difficulty. Summary of the Invention

[0005] Aiming at the defects existing in the prior art, the purpose of the present invention is to provide an excitation circuit for an electromagnetic conductivity sensor, which can effectively reduce costs while generating sine waves.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] An excitation circuit for an electromagnetic conductivity sensor, the excitation circuit includes: a square wave generating circuit, a frequency dividing circuit, a filtering circuit, and a driving circuit connected in sequence, and the driving circuit is connected to the transmitting coil of the electromagnetic conductivity sensor;

[0008] The square wave generating circuit is used to generate a quadruple-frequency square wave of the required sine wave and output it to the frequency dividing circuit;

[0009] The frequency division circuit is used to divide the received quadruple-frequency square wave to obtain four quadruple-frequency square waves, and any one of them is output to the filtering circuit;

[0010] The filtering circuit is used to filter one received quadruple-frequency square wave to obtain the required sine wave and output it to the driving circuit;

[0011] The driving circuit is used to excite the transmitting coil according to the received sine wave.

[0012] Furthermore, for the excitation circuit of an electromagnetic conductivity sensor as described above, the square wave generating circuit is a timer or PWM module of a single-chip microcomputer.

[0013] Furthermore, for the excitation circuit of an electromagnetic conductivity sensor as described above, the filtering circuit is specifically used to filter out the high-order harmonic components in one received quadruple-frequency square wave to obtain a sine wave with only DC component and fundamental wave component.

[0014] Furthermore, for the excitation circuit of an electromagnetic conductivity sensor as described above, the driving circuit includes: a digital potentiometer, a driving amplifier, and a DC-blocking capacitor connected in sequence, and the DC-blocking capacitor is connected to the transmitting coil;

[0015] The digital potentiometer is used to divide the received sine wave by resistance voltage division, control its own voltage division ratio through the single-chip microcomputer, and adjust the amplitude of the received sine wave according to needs;

[0016] The driving amplifier is used to improve the driving ability of the received sine wave;

[0017] The DC-blocking capacitor is used to filter out the DC component in the received sine wave to obtain a sine wave with only fundamental wave component to excite the transmitting coil.

[0018] Furthermore, for the excitation circuit of an electromagnetic conductivity sensor as described above, the frequency division circuit is composed of two interconnected D flip-flops.

[0019] Furthermore, for the excitation circuit of an electromagnetic conductivity sensor as described above, the phases of the four quadruple-frequency square waves are: 0°, 90°, 180°, and 270°.

[0020] Furthermore, for the excitation circuit of an electromagnetic conductivity sensor as described above, the filtering circuit is a low-pass filter.

[0021] The beneficial effect of the present invention is that: the present invention generates a sinusoidal alternating voltage through the method of square wave and low-pass filtering, and the generated sinusoidal alternating voltage excites the transmitting coil through the driving circuit, effectively reducing the cost. Description of the Drawings

[0022] Figure 1 This is a schematic diagram of the excitation circuit of an electromagnetic conductivity sensor provided in an embodiment of the present invention;

[0023] Figure 2 This is the circuit schematic diagram of the frequency division circuit provided in an embodiment of the present invention;

[0024] Figure 3 This is the circuit schematic diagram of the filter circuit provided in an embodiment of the present invention;

[0025] Figure 4 This is the input-output diagram of the filter circuit provided in an embodiment of the present invention. Detailed implementation manners

[0026] The present invention will be further described in detail below in conjunction with the specification drawings and specific implementation manners.

[0027] An excitation circuit of an electromagnetic conductivity sensor, the excitation circuit includes: a square wave generating circuit, a frequency division circuit, a filter circuit, and a driving circuit connected in sequence, and the driving circuit is connected to the transmitting coil of the electromagnetic conductivity sensor;

[0028] The square wave generating circuit is used to generate a quadruple-frequency square wave of the required sine wave and output it to the frequency division circuit;

[0029] The square wave generating circuit is a timer or PWM module of a single-chip microcomputer.

[0030] The frequency division circuit is used to divide the received quadruple-frequency square wave to obtain four quadruple-frequency square waves, and any one of them is output to the filter circuit;

[0031] The frequency division circuit is composed of two interconnected D flip-flops.

[0032] The phases of the four quadruple-frequency square waves are respectively: 0°, 90°, 180°, and 270°.

[0033] The filter circuit is used to filter one of the received quadruple-frequency square waves to obtain the required sine wave and output it to the driving circuit;

[0034] Specifically, the filter circuit is used to filter out the high-order harmonic components in one of the received quadruple-frequency square waves to obtain a sine wave with only DC components and fundamental wave components.

[0035] The filter circuit is a low-pass filter.

[0036] The driving circuit is used to excite the transmitting coil according to the received sine wave.

[0037] The driving circuit includes: a digital potentiometer, a driving amplifier, and a DC blocking capacitor connected in sequence, and the DC blocking capacitor is connected to the transmitting coil;

[0038] A digital potentiometer is used to divide the received sine wave by resistance voltage division, and the single-chip microcomputer controls its own voltage division ratio to adjust the amplitude of the received sine wave as needed.

[0039] A drive amplifier is used to improve the drive ability of the received sine wave.

[0040] A DC-blocking capacitor is used to filter out the DC component in the received sine wave to obtain a sine wave with only the fundamental wave component to excite the transmitting coil.

[0041] Embodiment 1

[0042] As Figures 1-4 shown, an excitation circuit for an electromagnetic conductivity sensor is used to provide a sinusoidal alternating voltage to the transmitting coil in the electromagnetic conductivity sensor. The excitation circuit includes: a square wave generating circuit 1, a frequency division circuit 2, a filtering circuit 4, and a driving circuit connected in sequence.

[0043] The square wave generating circuit 1 is used to output a quadruple-frequency square wave of the required sine wave. The square wave generating circuit 1 is a timer or PWM module of the single-chip microcomputer. The single-chip microcomputer outputs a quadruple-frequency square wave of the sine wave through the IO port. Most existing single-chip microcomputers include the PWM output function, so that the output square wave does not occupy the resources of the single-chip microcomputer at all, and the frequency can be slightly adjusted as needed without any modification to the hardware, increasing the scalability of the design.

[0044] The frequency division circuit 2 is used to output four quadruple-frequency square waves. As Figure 2 shown, the frequency division circuit 2 consists of two D flip-flops. The two D flip-flops are interconnected to output four square waves that divide the input signal by four, with phases of 0°, 90°, 180°, and 270° respectively, corresponding to Figure 2 QPWM0, QPWM90, QPWM180, and QPWM270 in, and these four square waves are used to output to the demodulation circuit 3 to participate in the processing of the sensor acquisition signal. Any one of these signals is used as the input of the subsequent filtering circuit 4.

[0045] As Figure 3 shown, the filtering circuit 4 is used to filter any one of the square waves QPWN0 output by the frequency division circuit 2 to generate a sine signal SINE0. The Fourier transform of a square wave can be expressed as the sum of its DC component, fundamental wave component, and high-order harmonic components. After passing through the filtering circuit 4, the high-order harmonic components in the square wave are filtered out, and only the DC component and the fundamental wave component remain in the signal, which is output to the driving circuit. Figure 4 is the input-output diagram of the filtering circuit 4, QPWN0 is the input, and SINE0 is the output. The filtering circuit 4 can be a low-pass filter, specifically a second-order low-pass filter.

[0046] The drive circuit is used to drive the transmitting coil according to the sine signal output by the filter circuit 4. The drive circuit includes a digital potentiometer 5, a drive amplifier 6, and a DC-blocking capacitor 7. The digital potentiometer 5 is controlled by a single-chip microcomputer, and divides the voltage of the output signal of the filter circuit 4, that is, the output sine wave, by means of resistor voltage division. By controlling the voltage division ratio of the digital potentiometer 5 by the single-chip microcomputer, the amplitude of the output signal can be adjusted as needed. Since the output capacity of the digital potentiometer 5 is weak, it is connected to the drive amplifier 6, and the transmitting coil is driven by the output of the drive amplifier 6. Since the DC impedance of the transmitting coil 8 is very small, the DC component in the signal will damage the transmitting coil. Therefore, a DC-blocking capacitor 7 is placed between the drive amplifier 6 and the transmitting coil 8 to filter out the DC component in the signal, and only the fundamental wave component in the signal is left to excite the transmitting coil 8.

[0047] The beneficial effects of the present invention are as follows:

[0048] 1. The design uses common devices. When some of these devices are out of production, it is easy to find other alternative devices without the need to redesign the circuit.

[0049] 2. The four-way square wave signals generated by using dual D flip-flops are used not only in the excitation circuit part but also in the demodulation circuit part, making full use of the functions of the devices. Moreover, D flip-flops are inexpensive and have a small package, which not only saves the circuit board space, reduces the wiring difficulty, but also saves costs.

[0050] 3. Using a digital potentiometer can change the amplitude of the excitation signal as needed without changing any circuit, thereby increasing the resolution of small-signal measurement.

[0051] Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and its equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. An excitation circuit for an electromagnetic conductivity sensor, characterized in that The excitation circuit includes: a square wave generating circuit, a frequency dividing circuit, a filtering circuit, and a driving circuit connected in sequence. The driving circuit is connected to the transmitting coil of the electromagnetic conductivity sensor; The square wave generating circuit is used to generate a quadruple-frequency square wave of the required sine wave and output it to the frequency dividing circuit; The frequency dividing circuit is used to divide the received quadruple-frequency square wave to obtain four quadruple-frequency divided square waves, and any one of them is output to the filtering circuit; The filtering circuit is used to filter one of the received quadruple-frequency divided square waves to obtain the required sine wave and output it to the driving circuit; specifically, the filtering circuit is used to filter out the high-order harmonic components in one of the received quadruple-frequency divided square waves to obtain a sine wave with only DC component and fundamental wave component; The driving circuit is used to excite the transmitting coil according to the received sine wave, and includes: a digital potentiometer, a driving amplifier, and a DC blocking capacitor connected in sequence. The DC blocking capacitor is connected to the transmitting coil; The digital potentiometer is used to divide the received sine wave by means of resistor voltage division, control its own voltage division ratio through a single-chip microcomputer, and adjust the amplitude of the received sine wave according to needs; The driving amplifier is used to improve the driving ability of the received sine wave; The DC blocking capacitor is used to filter out the DC component in the received sine wave to obtain a sine wave with only fundamental wave component to excite the transmitting coil.

2. The excitation circuit of an electromagnetic conductivity sensor according to claim 1, characterized in that The square wave generating circuit is a timer or PWM module of a single-chip microcomputer.

3. The excitation circuit of an electromagnetic conductivity sensor according to any one of claims 1-2, characterized in that The frequency dividing circuit is composed of two interconnected D flip-flops.

4. The excitation circuit of an electromagnetic conductivity sensor according to any one of claims 1-2, characterized in that, The phases of the four quadruple-frequency divided square waves are: 0°, 90°, 180°, and 270°.

5. The excitation circuit of an electromagnetic conductivity sensor according to any one of claims 1-2, characterized in that, The filtering circuit is a low-pass filter.

Images