A multi-channel voltage signal acquisition and processing circuit

Abstract

The present application belongs to the technical field of electronic design, and relates to a kind of multi-channel voltage signal acquisition and processing circuit.It includes, signal input terminal for receiving external signal, and external signal enters acquisition circuit through the terminal;Signal grouping acquisition module circuit, for signal grouping acquisition;Signal acquisition bus, for sending the signal collected to processing circuit;Reference voltage generation module circuit, for generating reference voltage, signal reference point of acquisition circuit and processing circuit is lifted to power supply negative pole, and the voltage value of the lifted voltage is the midpoint of the sampling range of the later-stage ADC;Signal processing module circuit, after the signal on the acquisition bus is protected by overvoltage limit and resistance voltage division, output is carried out.The remarkable effect of the present application is: realizing multi-channel signal acquisition and processing, solving the contradiction between the large number of input signals and the small number of ADC channels, and providing a reference for multi-channel instrument design and manufacturing.

Description

Technical Field

[0001] This invention belongs to the field of electronic design technology and relates to a multi-channel voltage signal acquisition and processing circuit. Background Technology

[0002] In industrial settings or other fields, when debugging and maintaining control systems, it is often necessary to test a large number of signals at once, typically at control cabinets or termination boxes where signals are concentrated in a regular pattern. Checking each signal individually with a multimeter is inefficient.

[0003] In addition to common single-channel signal measuring instruments (such as multimeters), multi-channel instruments are required in some special applications. Multi-channel instruments have many signal inputs, while microcontrollers and ADC (analog-to-digital converter) sampling chips have few sampling channels. Increasing the number of ADC sampling channels one-to-one would not only significantly increase the instrument cost but also make it difficult to achieve a compact and portable design. This creates a contradiction between the need for many signal input channels and the limited sampling channels of microcontrollers and ADCs.

[0004] Meanwhile, the sampling and processing circuit of measuring instruments often has the following requirements: 1) When the input signal to be measured is within the effective measurement range, ensure the accuracy of the processed signal; 2) When the input signal to be measured exceeds the effective measurement range, set up a corresponding protection mechanism to prevent damage to the microcontroller and ADC.

[0005] Therefore, it is necessary to design a multi-channel voltage signal acquisition and processing circuit to resolve the contradiction between the large number of input signals and the small number of ADC channels, and to provide a reference for the design and manufacture of multi-channel instruments. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a multi-channel voltage signal acquisition and processing circuit.

[0007] This invention is implemented as follows: a multi-channel voltage signal acquisition and processing circuit, comprising,

[0008] The signal under test input terminal is used to receive external signals, and the external signals enter the acquisition circuit through this part of the terminal;

[0009] Signal group acquisition module circuit, used for group acquisition of signals;

[0010] The signal acquisition bus is used to send the acquired signals to the processing circuit. Signals from each group of signal acquisition circuits can be sent to this bus, but only one group of acquisition signals is allowed to be sent to the bus at the same time.

[0011] The reference voltage generation module circuit is used to generate a reference voltage, which raises the signal reference point of the acquisition circuit and the processing circuit relative to the negative power supply. The raised voltage value is the midpoint of the sampling range of the subsequent ADC.

[0012] The signal processing module circuit outputs the signal from the acquisition bus after passing overvoltage limit protection and resistor voltage division.

[0013] As described above, in a multi-channel voltage signal acquisition and processing circuit, the signal enters the signal grouping acquisition module circuit through the signal input terminal under test. The signal grouping acquisition module circuit processes and decomposes the signal into several channels for acquisition. The acquired signal is sent to the signal processing module circuit through the signal acquisition bus. The reference voltage generation module circuit is used to generate a reference voltage.

[0014] The multi-channel voltage signal acquisition and processing circuit described above includes a signal grouping acquisition module circuit comprising:

[0015] A freewheeling diode is used to absorb the current generated after the relay coil is de-energized, preventing the generation of high-voltage back electromotive force.

[0016] When the relay coil is energized, it generates a magnetic field, which triggers the relay contacts to operate.

[0017] The relay contacts control whether the signal to be acquired is connected to the signal acquisition bus.

[0018] The input port of the microcontroller signal or the pre-stage driver circuit signal receives signals from the microcontroller or the microcontroller + MOSFET driver circuit, and then controls the relay to open or close.

[0019] The current-limiting resistor for the MOSFET drive signal prevents excessive drive current from damaging the preceding drive circuitry or the microcontroller.

[0020] Pull-down resistors for MOSFET drive signals prevent false triggering due to interference.

[0021] A MOSFET, as a controlled electronic switch, controls whether a relay coil is energized or de-energized.

[0022] As described above, a multi-channel voltage signal acquisition and processing circuit includes a reference voltage generation module circuit comprising:

[0023] The power input of the reference source module circuit is typically no higher than the supply voltage of the subsequent microcontroller; here it is set to 5V.

[0024] The current-limiting resistor is used to ensure the reliable operation of the voltage reference device. The resistance value of the current-limiting resistor is selected after calculation based on the operating current required in the voltage reference device's manual.

[0025] For voltage reference devices, choose TL431.

[0026] Filter capacitors are used to filter out noise from the voltage reference voltage.

[0027] In the multi-channel voltage signal acquisition and processing circuit described above, a 0.01uF filter capacitor is selected.

[0028] As described above, a multi-channel voltage signal acquisition and processing circuit includes a signal processing module circuit comprising:

[0029] Signal current limiting and voltage dividing resistors are used for voltage division and current limiting. When the signal under test is within the normal range, this resistor acts as a voltage dividing resistor; when the signal under test exceeds the normal range, this resistor acts as a current limiting resistor.

[0030] The signal voltage divider resistor 'a' is used to divide the voltage of the signal to be acquired.

[0031] The signal voltage divider resistor b is used to divide the voltage of the signal to be acquired.

[0032] A bidirectional TVS diode is used to prevent overvoltage across the signal voltage divider resistors a and b, and the current-limiting resistor.

[0033] The signal output port is used to output the signal after processing by the circuitry, so that the subsequent ADC can acquire it.

[0034] The significant advantage of this invention is that it enables multi-channel signal acquisition and processing, resolves the contradiction between a large number of input signals and a small number of ADC channels, and provides a reference for the design and manufacture of multi-channel instruments.

[0035] Because the circuit adopts a group acquisition and signal transmission bus architecture, the number of signal acquisition input interfaces can be easily expanded according to actual needs. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a multi-channel voltage signal acquisition and processing circuit.

[0037] In the diagram, 1. Input terminal for the signal under test, 2. Signal grouping and acquisition module circuit, 3. Signal acquisition bus, 4. Reference voltage generation module circuit, 5. Signal processing module circuit, 6. Positive input terminal for circuit power supply, 7. Negative input terminal for circuit power supply, 2-1. Freewheeling diode, 2-2. Relay coil, 2-3. Relay contact, 2-4. Input port for microcontroller signal or pre-amplifier drive circuit signal, 2-5. Current-limiting resistor for MOSFET drive signal, 2-6. Pull-down resistor for MOSFET drive signal, 2-7. MOSFET, 4-1. Power input terminal for reference source module circuit, 4-2. Current-limiting resistor, 4-3. Voltage reference device, 4-4. Filter capacitor, 5-1. Signal current-limiting and voltage-dividing resistor, 5-2. Signal voltage-dividing resistor a, 5-3. Signal voltage-dividing resistor b, 5-4. Bidirectional TVS diode, 5-5. Signal output port. Detailed Implementation

[0038] Considering the complex industrial control environments, the circuit needs to have positive and negative voltage measurement capabilities to handle a wider range of signal types and prevent damage to the measurement circuitry from reverse connections. Simultaneously, the circuit needs high-voltage protection to prevent abnormal voltage increases in the signal circuit due to interference or the introduction of high voltage (such as AC 220V) into the field signal loop, which could burn out the subsequent microprocessor.

[0039] This circuit enables the simultaneous measurement of multiple signals. The circuit's logic is as follows: 1) Group switching and acquisition of the signals to be measured; 2) Sending the acquired signals to the bus for processing; 3) Processing the signals in stages using a group processing approach; 4) Sending the processed signals to the microcontroller.

[0040] Because it adopts an architecture that collects signals in groups and sends them to the bus, the number of signal acquisition input interfaces can be easily expanded according to actual needs.

[0041] The signal under test is input at terminal 1, through which external signals enter the acquisition circuit. Six terminals are shown in the diagram, but the number can vary depending on actual requirements.

[0042] Signal group acquisition module circuit 2, as shown in the diagram, has each group responsible for acquiring 3 signals, but other numbers are also possible. Each group in this module circuit contains the following components:

[0043] 2-1: Freewheeling diode, which absorbs the current generated after the relay coil is de-energized, and prevents the generation of high voltage back electromotive force.

[0044] 2-2: The relay coil generates a magnetic field when energized, which triggers the relay contacts to operate.

[0045] 2-3: Relay contacts control whether the signal to be acquired is connected to the signal acquisition bus.

[0046] 2-4: Input port for microcontroller signals or pre-amplifier drive circuit signals, receiving signals from the microcontroller or microcontroller + MOSFET drive circuit, and then controlling the relay to engage or disengage.

[0047] 2-5: Current limiting resistor for MOSFET drive signal, to prevent excessive drive current from damaging the preceding drive circuit or microcontroller.

[0048] 2-6: Pull-down resistor for MOSFET drive signal to prevent false triggering due to interference.

[0049] 2-7: MOSFET, as a controlled electronic switch, controls the relay coil to be energized or de-energized.

[0050] Signal acquisition bus 3: Signals from each group of signal acquisition circuits can be sent to this bus, but only one group of acquisition signals is allowed to be sent to the bus at any given time. The acquired signals are then sent to the processing circuit through this bus.

[0051] Reference voltage generation module circuit 4 is responsible for generating a reference voltage, raising the signal reference point of the acquisition and processing circuit relative to the negative power supply. The raised voltage value is the midpoint of the sampling range of the subsequent ADC. Here, it is assumed that the ADC sampling range is 0-5V, and the reference voltage value is 2.5V. Raising the reference voltage of the signal acquisition and processing circuit aims to achieve the acquisition of both positive and negative voltage signals. After processing, if the output signal range relative to the reference point is -2.5V to +2.5V, the voltage range relative to the negative power supply is 0-5V, satisfying the requirement that the ADC can only acquire positive voltages, and thus achieving the acquisition of both positive and negative voltages of the signal under test. (Note: Usually, the negative power supply is the only reference point for the signal; this circuit also has a 2.5V voltage reference point.) This module circuit specifically includes the following components:

[0052] 4-1: The power input terminal of the reference source module circuit is usually no higher than the power supply voltage of the subsequent microcontroller; here it is set to 5V.

[0053] 4-2: Current-limiting resistor. To ensure reliable operation of the voltage reference device, a current-limiting resistor is needed to provide a reliable operating current. The value of the current-limiting resistor needs to be calculated and selected based on the operating current requirements specified in the voltage reference device's datasheet. Assuming a TL431 voltage reference is selected, the datasheet specifies an operating current range of 1-100mA. The desired voltage reference value is 2.5V. Therefore, the voltage across the current-limiting resistor = the module's power supply voltage - the reference voltage = 5.0V - 2.5V = 2.5V. Thus, the current-limiting resistor value should be between 25Ω and 2.5KΩ; here, a 1KΩ resistor is chosen.

[0054] 4-3: Voltage reference device, here we choose TL431, but other devices with similar functions can also be used. Based on the selected voltage reference device and corresponding peripheral circuits, the final module circuit is formed.

[0055] 4-4: Filter capacitor, used to filter out voltage reference voltage noise. This noise is generated by the TL431 itself and by external interference. The capacitor value should generally not exceed 0.1uF. After the circuit design is complete, the optimal capacitor value can be selected by observing the waveform stability through experiments. Based on my own testing, a 0.01uF capacitor was selected for this module.

[0056] Signal processing module circuit 5 processes the signal from the acquisition bus through overvoltage limit protection and resistor voltage division before outputting it. The output range is 0-5V (relative to the negative power supply 7) within the signal acquisition range of the subsequent ADC, and -2.5V to +2.5V relative to the reference voltage (2.5V) of the acquisition circuit. This module circuit specifically includes the following components:

[0057] 5-1: Signal current limiting and voltage divider resistor. When the signal under test is within the normal range, this resistor acts as a voltage divider; when the signal under test exceeds the normal range, this resistor prevents excessive current from flowing through 5-4, acting as a current limiting resistor. Five resistors of the same type are set for each channel; the values ​​and power ratings of these resistors need to be obtained through detailed calculations.

[0058] 5-2: Signal voltage divider resistor a. This resistor is used to divide the signal being acquired; its value needs to be obtained through detailed calculation.

[0059] 5-3: Signal voltage divider resistor b. This resistor is used to divide the signal being acquired; its value needs to be determined through detailed calculations.

[0060] 5-4: Bidirectional TVS diode, to prevent overvoltage across the current-limiting resistors 5-2 and 5-3.

[0061] 5-5: Signal output port, outputs the signal after processing by the circuit so that the subsequent ADC can acquire it.

[0062] The selection guidelines for this section of components are as follows:

[0063] First, set the measurement range of the signal to be measured. Considering that industrial control system signals are generally DC 24V, a certain margin is allowed, and the measurement range is initially set to be no less than -30V to +30V.

[0064] TVS Selection. When selecting a TVS, the leakage current should be as low as possible to minimize its impact on the accuracy of the resistor voltage divider. After consulting the datasheet and comparing options, the SMBJ30CA TVS was selected. It has a leakage current of 1uA, and according to the datasheet, its cutoff voltage is ±30V and its maximum clamping voltage is ±48.4V.

[0065] Signal voltage divider resistor selection. 1) Resistance value selection: The maximum voltage across the two signal voltage divider resistors is the maximum clamping voltage of the TVS (±48.4V). In this case, it is necessary to ensure that the processed output signal is within the ADC sampling range (0-5V), that is, relative to the reference voltage of the acquisition circuit, the voltage range of the output at terminal 5-5 needs to be within the range of -2.5V to +2.5V. Therefore, the voltage division ratio R... 5-3 / (R 5-2 +R 5-3)≤2.5 / 48.4≈0.05. Based on the voltage divider ratio, R5-2 is typically rated at 200kΩ, and R5-3 at 10kΩ, resulting in a voltage divider ratio of 0.0476, which meets the above calculation requirements. 2) Power selection. When R... 5-2 and R 5-3 The power consumption is highest when the maximum voltage is present at both ends. Calculations show that the power consumption of the two resistors at this time is 0.53mW and 10.58mW respectively. Therefore, a 125mW resistor in a common 0805 package can meet the requirements.

[0066] Signal current limiting and voltage divider resistor selection. 1) Resistance value selection: Given that the sum of the signal voltage divider resistors (serial numbers 5-2 and 5-3) is 210kΩ, and considering that the TVS cutoff voltage is ±30V, and the signal measurement range already meets the preliminary design, the resistor should minimize signal attenuation to improve the signal measurement accuracy within the affected range. Take 1 / 21 of the sum of the signal voltage divider resistors, i.e., 10kΩ. 2) Power selection: Considering the worst-case industrial conditions, with AC 220V serially connected to the signal under test, the voltage across the resistor = voltage of the signal under test - maximum clamping voltage across the TVS = 240V - 48.4V = 191.6V (actual AC voltage is generally slightly higher than 220V; 240V is chosen based on experience). The power consumed by the resistor at this time = U² / R = (191.6V)² / 10kΩ ≈ 3.67W. Allowing for a margin, a 5W resistor is selected. If you consider the component height and ease of surface mount soldering when building the circuit, you can choose five 2512 package surface mount resistors, each with a power dissipation of 1W. The attached diagram shows the five resistors in series. Other numbers of resistors can also be used in series to meet the resistance and power requirements.

[0067] Since a current-limiting resistor 5-1 has been added to the basis of serial numbers 5-2 and 5-3, the effective signal measurement range will be wider. The new signal measurement range is calculated as follows: Now assuming that the voltage across the TVS is exactly ±30V, the voltage of the signal to be measured is calculated to be ±30V / 210K*220K=±31.43V, that is, the final designed effective signal measurement range is -31.43V~+31.43V.

[0068] The circuit's working principle is described below.

[0069] Signal grouping and acquisition module circuit: This part uses a common MOSFET driver circuit. A single MOSFET simultaneously drives a group (multiple relays, shown in the diagram as three, but other numbers are also possible) of relay coils, thereby controlling the relay contacts. In the above circuit, one coil corresponds to one contact. This part of the circuit can also be configured so that one relay coil corresponds to multiple contacts. A freewheeling diode is connected in anti-parallel across the coil to prevent high voltage from being induced across the relay coil when the MOSFET is turned off, thus preventing damage to surrounding components. The dashed box in the diagram shows one group of acquisition circuits. Because a signal bus is used as a bridge, the acquisition circuit can be easily expanded according to the required number of acquisition channels (by copying the circuit in the dashed box). The microcontroller controls the closing of each group of relays in a time-division manner, achieving signal grouping and time-division acquisition.

[0070] Reference voltage generation module circuit: Connect according to the TL431 datasheet to generate a 2.5V reference voltage at terminals 4-5. The signal from terminals 4-5 is sent to the ADC for sampling to provide a voltage calibration source. This terminal also needs to be led out and connected to the zero point of the signal under test (e.g., when testing the control cabinet signal to ground voltage, this terminal is led out and connected to the cabinet casing or ground wire via a wire clamp). This 2.5V reference voltage line is simultaneously sent to the signal processing module circuit (serial number 5) as the zero reference point for signal processing.

[0071] Signal processing module circuit: During normal measurement, the signal is collected from the signal terminals in groups to the signal bus, then divided by resistors and returned to the zero point of the signal under test (terminals 4-5 in the figure). The divided signal is then output from terminal 5-5 to the ADC for acquisition. When the signal under test exceeds the measurement range, the TVS (Transient Voltage Suppressor) kicks in, clamping the voltage within a safe value to prevent damage to subsequent sampling devices such as the ADC. At this time, terminal 5-5 cannot linearly feedback the status of the signal under test.

Claims

1. A multi-channel voltage signal acquisition and processing circuit, characterized in that: include, The signal input terminal (1) is used to receive external signals, and the external signals enter the acquisition circuit through this terminal. Signal group acquisition module circuit (2) is used to acquire signals in groups; The signal acquisition bus (3) is used to send the acquired signals to the processing circuit. The signals of each group of signal acquisition circuits can be sent to the bus, but only one group of acquisition signals is allowed to be sent to the bus at the same time. The reference voltage generation module circuit (4) is used to generate a reference voltage, raising the signal reference point of the acquisition circuit and the processing circuit relative to the negative power supply. The raised voltage value is the midpoint of the sampling range of the subsequent ADC. The signal processing module circuit (5) outputs the signal from the acquisition bus after it has been subjected to overvoltage limit protection and resistor voltage division.

2. The multi-channel voltage signal acquisition and processing circuit as described in claim 1, characterized in that: The signal enters the signal grouping acquisition module circuit (2) through the signal input terminal (1) under test. It is decomposed into several signals and acquired by the signal grouping acquisition module circuit (2). The acquired signal is sent to the signal processing module circuit (5) through the signal acquisition bus (3). The reference voltage generation module circuit (4) is used to generate the reference voltage.

3. The multi-channel voltage signal acquisition and processing circuit as described in claim 2, characterized in that: The signal group acquisition module circuit (2) includes, The freewheeling diode (2-1) is used to absorb the current generated after the relay coil is de-energized, preventing the generation of high-voltage back electromotive force. The relay coil (2-2), when energized, generates a magnetic field, triggering the relay contacts to operate. Relay contacts (2-3) control whether the signal to be acquired is connected to the signal acquisition bus. The input ports (2-4) of the microcontroller signal or the pre-stage driver circuit signal receive signals from the microcontroller or the microcontroller + MOSFET driver circuit, and then control the relay to open or close. The MOSFET drive signal current-limiting resistor (2-5) prevents excessive drive current from damaging the preceding drive circuit or microcontroller. Pull-down resistors (2-6) for MOSFET drive signals are used to prevent false triggering due to interference. MOSFETs (2-7) act as controlled electronic switches to control the relay coil to be energized or de-energized.

4. The multi-channel voltage signal acquisition and processing circuit as described in claim 3, characterized in that: The reference voltage generation module circuit (4) includes, The power input terminal (4-1) of the reference source module circuit is typically no higher than the power supply voltage of the subsequent microcontroller; here it is set to 5V. The current-limiting resistor (4-2) is used to ensure the reliable operation of the voltage reference device. The resistance value of the current-limiting resistor is selected after calculation based on the operating current required in the voltage reference device manual. For the voltage reference device (4-3), select TL431. The filter capacitor (4-4) is used to filter out noise from the voltage reference voltage.

5. The multi-channel voltage signal acquisition and processing circuit as described in claim 4, characterized in that: The filter capacitor (4-4) is a 0.01uF capacitor.

6. The multi-channel voltage signal acquisition and processing circuit as described in claim 5, characterized in that: The signal processing module circuit (5) includes, Signal current limiting and voltage dividing resistor (5-1) is used for voltage dividing and current limiting. When the signal under test is within the normal range, this resistor acts as a voltage dividing resistor; when the signal under test exceeds the normal range, this resistor acts as a current limiting resistor. The signal voltage divider resistor a(5-2) is used to divide the signal to be acquired. The signal voltage divider resistor b(5-3) is used to divide the signal to be acquired. A bidirectional TVS diode (5-4) is used to prevent overvoltage across the current-limiting resistors of signal voltage divider resistors a (5-2) and b (5-3). The signal output port (5-5) is used to output the signal after processing by the circuit so that the subsequent ADC can acquire it.

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