A high-precision programmable strain bridge excitation source

Abstract

This invention belongs to the field of strain gauge excitation technology, solving the problems of existing strain gauge excitation sources, such as inability to adjust, slightly low accuracy, and poor versatility. It provides a high-precision, programmable strain gauge excitation source. A reference reference source circuit outputs a reference voltage to a programmable excitation reference circuit. A control circuit controls the positive and negative excitation reference voltages output by the programmable excitation reference circuit, which are amplified, buffered, and flipped by an excitation reference amplifier circuit to generate positive and negative excitation voltages. An excitation voltage driving circuit drives the positive and negative excitation voltages and outputs them to the strain gauge, while automatically compensating for the voltage drop of the excitation voltage applied to the strain gauge. This invention provides high-precision output excitation voltage, strong versatility, and applicability to most strain signal acquisition equipment and instruments. It uses integrated devices to construct a power supply excitation circuit with continuously adjustable positive and negative excitation voltages, compensating for the voltage drop caused by transmission lines in hardware.

Description

Technical Field

[0001] This invention belongs to the field of strain bridge excitation technology, specifically relating to a high-precision programmable strain bridge excitation source. Background Technology

[0002] The output of a strain gauge bridge is closely related to the excitation voltage applied to it, and the precision of the excitation voltage directly determines the precision of the strain measurement. In practical engineering applications, strain measurement systems need to achieve a measurement accuracy better than 0.05%FS.

[0003] Currently, most bridge excitation sources use constant voltage power supplies, but their inherent ripple cannot be completely eliminated. The offset value of a typical industrial-grade constant voltage source is tens of mV, with errors mostly exceeding 1%. This level of offset voltage causes significant errors in high-precision strain measurement systems. If we take a bridge excitation of 5V, the excitation voltage ripple is δ, with a value of 50mV. The resistance of the strain gauge is a standard 120Ω, and the sensitivity coefficient K is set to 2. When the measured structure generates 1000 micro-strains, the measurement error caused by the excitation noise is 1%, equivalent to 10 micro-strains. For high-precision measuring instruments like strain measurement systems, especially when measuring large strain signals, this error is unacceptable. Furthermore, in actual measurement processes, excessively long measurement distances can cause a voltage drop due to the transmission line resistance. Under these conditions, the measurement error caused by a measurement distance of 100 meters can exceed 3%.

[0004] Existing bridge excitation sources are typically suitable for specific projects, and the bridge excitation is a fixed value, usually 2.5V or 10V, which cannot be adjusted. At the same time, the accuracy is slightly low and the versatility is poor. However, the excitation voltage values ​​required by current strain gauges are different. In order to meet different application scenarios and different testing requirements, adapt to the compatibility of various strain gauges, and improve the versatility of strain gauges, it is necessary to develop a high-precision, programmable excitation source to overcome the shortcomings of the aforementioned bridge excitation sources. Summary of the Invention

[0005] In order to solve at least one of the above-mentioned technical problems in the prior art, the present invention provides a high-precision programmable strain bridge excitation source.

[0006] The present invention is achieved by the following technical solution: a high-precision programmable strain gauge bridge excitation source, including a reference reference source circuit, a programmable excitation reference circuit, an excitation reference amplifier circuit, an excitation voltage driving circuit, and a control circuit; the reference reference source circuit outputs a reference reference voltage to the programmable excitation reference circuit, the control circuit controls the positive and negative excitation reference voltages output by the programmable excitation reference circuit to be amplified, buffered, and flipped by the excitation reference amplifier circuit to generate positive and negative excitation voltages, and the excitation voltage driving circuit drives the positive and negative excitation voltages and outputs them to the strain gauge bridge, while automatically feeding back and compensating for the voltage drop of the excitation voltage applied to the strain gauge bridge.

[0007] Preferably, the reference source circuit includes a voltage reference chip REF5025 and an operational amplifier OPA333. The input terminal of the operational amplifier OPA333 is connected to the output terminal of the voltage reference chip REF5025, serving as a voltage follower, and an RC low-pass filter is added.

[0008] The programmable excitation reference circuit includes a digital-to-analog converter (DAC8552) and peripheral circuitry. Port VREF of the DAC8552 is connected to port VREF of the reference source circuit. Ports DADIN, DASCLK, and DASYNC of the DAC8552 are connected to the control circuit. Port V of the DAC8552... Out A and V Out B outputs positive and negative excitation reference voltages respectively.

[0009] Preferably, the excitation reference amplifier circuit includes positive and negative reference voltage amplifier circuits composed of an instrumentation amplifier INA819 and peripheral circuits. The non-inverting input of the instrumentation amplifier INA819 in the positive reference voltage amplifier circuit will input V... Out The positive excitation reference voltage output by A is passed through an external resistor R. 17 Amplify and output the positive excitation voltage from the PV port. The non-inverting input of the instrumentation amplifier INA819 in the negative reference voltage amplifier circuit will amplify and output the positive excitation voltage. Out The negative excitation reference voltage output by B is passed through an external resistor R. 20 Amplify and output the negative excitation voltage from the NV port.

[0010] Preferably, the excitation voltage driving circuit is divided into positive and negative excitation voltage driving circuits. The positive excitation voltage driving circuit includes a switching regulator LT8608, an operational amplifier LT1678, a programmable linear regulator LT3045, and peripheral circuitry. Port PVI of the programmable linear regulator LT3045 is connected to the output port PV of the positive reference voltage amplifier circuit. The positive excitation voltage is output from port VP2 of the programmable linear regulator LT3045. The output interface of port VP2 of the programmable linear regulator LT3045 is EX+, which is connected to a resistor R. 42The transmission line provides a positive excitation voltage to the A terminal of the strain gauge bridge. The interface connected to the port PVO of the programmable linear regulator LT3045 is EXS+. The EXS+ interface is directly connected to the A terminal of the strain gauge bridge. The actual excitation voltage across the strain gauge bridge can be fed back to the port PVO through the EXS+ interface, which increases the excitation voltage VP2 output by the programmable linear regulator LT3045. When it reaches the A terminal of the strain gauge bridge through the transmission line, VP2 drops to the actual set positive excitation voltage.

[0011] The negative excitation voltage drive circuit includes a switching regulator LT8330, an operational amplifier LT1678, a programmable linear regulator LT3094, and peripheral circuitry. Port NVI of the programmable linear regulator LT3094 is connected to the output port NV of the negative reference voltage amplifier circuit. The negative excitation voltage is output from port VN2 of the programmable linear regulator LT3094. The output interface of port VN2 of the programmable linear regulator LT3094 is EX-, connected via a resistor R. 43 The transmission line provides a negative excitation voltage to the strain gauge bridge. The interface connected to port NVO of the programmable linear regulator LT3094 is EXS-. The EXS- interface is directly connected to the C terminal of the strain gauge bridge. The actual excitation voltage across the strain gauge bridge can be fed back to port NVO through the EXS- interface, which increases the excitation voltage VN2 output by LT3045. When VN2 reaches the C terminal of the strain gauge bridge through the transmission line, it drops to the actual set negative excitation voltage.

[0012] Preferably, a self-feedback power supply voltage circuit for a linear regulator is provided between the switching regulator LT8608 and the operational amplifier LT1678 in the positive excitation voltage drive circuit. The switching regulator LT8608 adjusts the feedback pin FB to the first value. According to the voltage divider principle of resistors R22 and R23, the output voltage of the operational amplifier LT1678 is clamped to the second value. The negative input terminal of the operational amplifier is the positive excitation voltage VP2, and the positive input terminal is the power supply voltage VP1 of LT3045. The power supply voltage VP1 is automatically adjusted according to the positive excitation voltage VP2 so that the difference between VP2 and VP1 is always equal to the second value.

[0013] Preferably, a self-feedback supply voltage circuit of a linear regulator is provided between the switching regulator LT8830 and the operational amplifier LT1678 in the negative excitation voltage drive circuit. The switching regulator LT8830 adjusts the feedback pin FB to the first value. According to the voltage divider principle of resistors R29 and R30, the output voltage of the operational amplifier LT1678 is clamped to the second value. The negative input terminal of the operational amplifier is the negative excitation voltage VN2, and the positive input terminal is the supply voltage VN1 of LT3094. The supply voltage VN1 is automatically adjusted according to the negative excitation voltage VN2 so that the difference between VN2 and VN1 is always equal to the second value.

[0014] Preferably, the first value is 0.778V and the second value is 1V.

[0015] Preferably, it also includes a current monitoring circuit. The current monitoring circuit module includes a current monitor SQ52201. The positive excitation voltage VP2 output by the programmable linear regulator LT3045 provides positive excitation to the strain gauge bridge through the EX+ interface. A resistor R is connected in series between VP2 and EX+. 36 The input terminals IN+ and IN- of the current monitor SQ52201 are respectively connected to resistor R. 37 Resistance R 38 With resistance R 36 The two ends are connected together, and a capacitor C is also connected between the input terminals IN+ and IN- of the current monitor SQ52201. 34 The SCL and SDA ports of the current monitor SQ52201 are connected to the control circuit to control the current monitor SQ52201 to complete the current measurement and detect the current magnitude when there is a load in real time.

[0016] Preferably, the control circuit includes an ARM microcontroller STM32F407ZGT6 and peripheral circuits. The control circuit acquires the PVO and NVO port voltages in the excitation voltage drive circuit, sets the excitation voltage value to be adjusted by the PID controller, and continuously adjusts the input value of the digital-to-analog converter in the programmable excitation reference circuit based on the feedback values ​​of the PVO and NVO ports, so that the excitation voltage value at both ends of the strain gauge bridge continuously approaches the set excitation voltage value, thereby obtaining a high-precision excitation voltage at both ends of the strain gauge bridge.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] This invention employs integrated devices to construct a power supply excitation circuit with continuously adjustable positive and negative excitation voltages. It compensates for the voltage drop caused by the transmission line in hardware, and uses hardware to maintain the voltage difference between the output and input of the linear regulator at a relatively small value, ensuring the conversion efficiency of the linear regulator, reducing heat loss, reducing the heat generation of the linear regulator chip, and ensuring the performance of the circuit. Furthermore, it utilizes the PID excitation voltage compensation feedback regulation method to enhance the accuracy of the output excitation voltage.

[0019] The excitation voltage output range of the bridge in this invention is -10V to +10V, with an accuracy better than (0.012%SET+2mV). It has high output excitation voltage precision, strong versatility, and can be applied to most strain signal acquisition related equipment and instruments. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the strain gauge bridge excitation source circuit structure of the present invention;

[0022] Figure 2 This is a schematic diagram of the reference source circuit structure of the present invention;

[0023] Figure 3 This is a schematic diagram of the programmable excitation reference circuit structure of the present invention;

[0024] Figure 4 This is a schematic diagram of the excitation reference amplifier circuit structure of the present invention.

[0025] Figure 5 This is a schematic diagram of the positive excitation voltage drive circuit structure of the present invention;

[0026] Figure 6 This is a schematic diagram of the negative excitation voltage drive circuit structure of the present invention;

[0027] Figure 7 This is a schematic diagram of the current monitoring circuit structure of the present invention;

[0028] Figure 8 This is a schematic diagram of the measurement circuit structure when the transmission line resistance is present in this invention;

[0029] Figure 9 This is a flowchart of the PID control in this invention;

[0030] Figure 10 The above are simulation results of the excitation circuit under ideal conditions (transmission line resistance is 0) provided in the embodiments of the present invention.

[0031] Figure 11 The simulation results of the excitation circuit under actual conditions (transmission line resistance is not 0) provided in the embodiments of the present invention are as follows. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] It should be noted that the structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportional relationships, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should fall within the scope of the technical content disclosed in the present invention. It should be noted that in this specification, relational terms such as "first" and "second" are only used to distinguish one entity from several other entities, and do not necessarily require or imply any actual relationship or order between these entities.

[0034] This invention provides an embodiment:

[0035] like Figure 1 As shown, a high-precision programmable strain gauge bridge excitation source includes a reference reference source circuit, a programmable excitation reference circuit, an excitation reference amplifier circuit, an excitation voltage drive circuit, and a control circuit. The reference reference source circuit outputs a reference reference voltage to the programmable excitation reference circuit. The control circuit controls the positive and negative excitation reference voltages output by the programmable excitation reference circuit to be amplified, buffered, and flipped by the excitation reference amplifier circuit to generate positive and negative excitation voltages. The excitation voltage drive circuit drives the positive and negative excitation voltages and outputs them to the strain gauge bridge, while automatically feeding back and compensating for the voltage drop of the excitation voltage applied to the strain gauge bridge.

[0036] like Figure 2 As shown, the reference source circuit includes a voltage reference chip REF5025 and an operational amplifier OPA333. REF5025 can provide a low-noise, low-temperature-drift, and high-precision reference voltage. The input terminal of the operational amplifier OPA333 is connected to the output terminal of the voltage reference chip REF5025 as a voltage follower. An RC low-pass filter is added to reduce noise in the reference ground, so that the output 2.5V reference voltage has high accuracy.

[0037] like Figure 3 As shown, the programmable excitation reference circuit includes a digital-to-analog converter (DAC8552) and peripheral circuitry. Port VREF of the DAC8552 is connected to port VREF of the reference source circuit. Ports DADIN, DASCLK, and DASYNC of the DAC8552 are connected to the control circuit. Port V of the DAC8552... Out A and V Out B outputs positive and negative excitation reference voltages respectively.

[0038] In this embodiment, the programmable excitation reference circuit is implemented using a 16-bit programmable D / A analog-to-digital converter DAC8552, with a step size of 2.5V / 2. 16=0.038mV, when the excitation voltage is 5V, the maximum output error is 3.8×10 -5 V / 5V = 0.00076%, indicating high DAC output accuracy. Ports DADIN, DASCLK, and DASYNC are connected to the control circuit, used to control the analog output value of the DAC8552 via a binary input code, which can be any value X / 2. 16 The reference base value is 1 times the value of X, where X ranges from 0 to 2. 16 The integer between [values], since the reference voltage is 2.5V, the output port V of the DAC8552 is [value]. Out A and V Out The maximum analog output value of B is 2.5V. Out The 0-2.5V output from A is used as the positive excitation reference voltage to drive V. Out The 0-2.5V output from B is used as the negative excitation reference voltage, and a high-precision excitation reference voltage is obtained from the DAC.

[0039] like Figure 4 As shown, an excitation reference voltage amplifier circuit is needed to amplify and buffer the positive excitation reference voltage, and to amplify, buffer, and flip the negative excitation reference voltage. The excitation reference amplifier circuit includes positive and negative reference voltage amplifier circuits composed of an instrumentation amplifier INA819 and peripheral circuitry. The INA819 is a high-precision instrumentation amplifier that offers low power consumption and can operate over a very wide single or dual supply voltage range. Its gain can be set arbitrarily from 1 to 10,000 ohms using a single external resistor. The non-inverting input of the instrumentation amplifier INA819 in the positive reference voltage amplifier circuit will... Out The 0-2.5V positive excitation reference voltage output by A is passed through an external resistor R. 17 Amplified 4 times, it outputs a 0-10V positive excitation voltage from the PV port. The non-inverting input of the instrumentation amplifier INA819 in the negative reference voltage amplifier circuit will... Out The 0-2.5V negative excitation reference voltage output by B is passed through an external resistor R. 20 It amplifies the voltage by 4 times and outputs a negative excitation voltage of 10V to 0V from the NV port.

[0040] Because the driving capability of the INA819 instrumentation amplifier is weak, an excitation voltage drive circuit is needed to improve the driving capability of the positive and negative excitation voltages output by the excitation reference voltage amplifier circuit. Furthermore, in actual measurements, the strain gauge R... bridge The bonding location is often far from the testing equipment, requiring long wires to connect the strain gauge to the strain signal testing equipment. This results in a significant increase in the resistance R of the wires. 42 and R 43The generation of a voltage difference leads to a deviation between the actual excitation voltage applied to terminals A and C of the bridge circuit and the set value, resulting in measurement errors. Therefore, a high-precision excitation source is very important for strain signal measurement. Thus, the excitation voltage drive circuit also needs to be able to automatically compensate for the remote excitation voltage so that the excitation voltage at terminals A and C is the actual set excitation voltage.

[0041] like Figure 5 , Figure 6 , Figure 8 As shown, the excitation voltage drive circuit is divided into positive and negative excitation voltage drive circuits. The positive excitation voltage drive circuit includes a switching regulator LT8608, an operational amplifier LT1678, a programmable linear regulator LT3045, and peripheral circuitry. Port PVI of the programmable linear regulator LT3045 is connected to the output port PV of the positive reference voltage amplifier circuit. The positive excitation voltage is output as a larger current positive excitation voltage from port VP2 of the programmable linear regulator LT3045, improving the driving capability of the positive excitation voltage for driving the strain gauge bridge. The output interface of port VP2 of the programmable linear regulator LT3045 is EX+. Since the resistance of the relatively long transmission line cannot be ignored, its resistance is R. 42 Through a resistor R 42 The transmission line provides a positive excitation voltage to terminal A of the strain gauge bridge. The interface connected to port PVO of the programmable linear regulator LT3045 is EXS+. The EXS+ interface is directly connected to terminal A of the strain gauge bridge. The actual excitation voltage across the strain gauge bridge can be fed back to port PVO through the EXS+ interface, thereby increasing the excitation voltage VP2 output by the programmable linear regulator LT3045. When VP2 reaches terminal A of the strain gauge bridge through the transmission line, it drops to the actual set positive excitation voltage. This reduces the measurement error caused by the excessively long transmission line when measuring strain signals, ensures high-precision excitation voltage output, and improves the accuracy of strain signal measurement.

[0042] Meanwhile, as a low dropout linear regulator, the LT3045's port PV voltage is derived from the amplified excitation reference voltage, and its value is adjustable. If the LT3045's supply voltage VP1 is a fixed value, then when the port voltage is low, the voltage drop will be large, which will reduce the LT3045's conversion efficiency and increase losses. This energy will be converted into heat, causing the chip to heat up and affecting the performance of the output excitation voltage. Therefore, this invention uses the switching regulator LT8608 and the operational amplifier LT1678 to design a self-feedback supply voltage circuit for the linear regulator.

[0043] The switching regulator LT8608 adjusts the feedback pin FB to 0.778V. Based on the voltage divider principle of resistors R22 and R23, the output voltage of the operational amplifier LT1678 is clamped at 1V. The negative input of the operational amplifier is the positive excitation voltage VP2, and the positive input is the supply voltage VP1 of the LT3045, which is output by the switching regulator LT8608. At this time, the LT8608 will automatically adjust the supply voltage VP1 according to the positive excitation voltage VP2 based on the voltage of the feedback pin FB and the output characteristics of the operational amplifier, so that the difference between VP2 and VP1 always maintains a fixed voltage value of 1V. This not only improves the conversion efficiency of the linear regulator, but also reduces losses, thereby reducing the heat of the chip and keeping the heat of the chip at a stable value, thus improving the stability of the output excitation voltage.

[0044] The negative excitation voltage drive circuit includes a switching regulator LT8330, an operational amplifier LT1678, a programmable linear regulator LT3094, and peripheral circuitry. Port NVI of the programmable linear regulator LT3094 is connected to the output port NV of the negative reference voltage amplifier circuit. The negative excitation voltage, after passing through the programmable linear regulator LT3094, can output a larger current negative excitation voltage from port VN2, improving the driving capability of the negative excitation voltage for driving the strain gauge bridge. The output interface of port VN2 of the programmable linear regulator LT3094 is EX-. Due to the non-negligible resistance of the relatively long transmission line, its resistance is R. 43 Through a resistor R 43 The transmission line provides a negative excitation voltage to the strain gauge bridge. The NVO port of the programmable linear regulator LT3094 is connected to the EXS- interface, which is directly connected to the C terminal of the strain gauge bridge. The EXS- interface can feed back the actual excitation voltage across the strain gauge bridge to the NVO port, thereby increasing the excitation voltage VN2 output by the LT3045. When VN2 reaches the C terminal of the strain gauge bridge through the transmission line, it drops to the actual set negative excitation voltage. This reduces the measurement error caused by the excessively long transmission line distance when measuring the strain signal, ensures high-precision excitation voltage output, and improves the accuracy of the measured strain signal.

[0045] Meanwhile, as a low dropout linear regulator, the LT3094's NV port voltage is derived from the amplified excitation reference voltage, and its value is adjustable. If the LT3094's supply voltage VN1 is a fixed value, then when the port voltage is low, the voltage drop will be large, which will reduce the LT3094's conversion efficiency and increase losses. This energy will be converted into heat, causing the chip to heat up and affecting the performance of the output excitation voltage.

[0046] A self-feedback supply voltage circuit for a linear regulator is set between the switching regulator LT8830 and the operational amplifier LT1678 in the negative excitation voltage drive circuit. The switching regulator LT8830 adjusts the feedback pin FB to 0.778V. According to the voltage divider principle of resistors R29 and R30, the output voltage of the operational amplifier LT1678 is clamped at 1V. The negative input terminal of the operational amplifier is the negative excitation voltage VN2, and the positive input terminal is the supply voltage VN1 of LT3094, which is output by the switching regulator LT8330. At this time, LT8330 will automatically adjust the supply voltage VN1 according to the negative excitation voltage VN2 based on the voltage of the feedback pin FB and the output characteristics of the operational amplifier, so that the difference between VN2 and VN1 is always equal to 1V. This not only improves the conversion efficiency of the linear regulator, but also reduces losses, thereby reducing the heat generation of the chip and keeping the heat of the chip at a stable value, which greatly improves the stability of the output excitation voltage.

[0047] like Figure 7 As shown, it also includes a current monitoring circuit. The current monitoring circuit module includes a current monitor SQ52201. The positive excitation voltage VP2 output by the programmable linear regulator LT3045 provides positive excitation to the strain gauge bridge through the EX+ interface. A 3mΩ resistor R is connected in series between VP2 and EX+. 36 The input terminals IN+ and IN- of the current monitor SQ52201 are respectively connected to resistor R. 37 Resistance R 38 With resistance R 36 The two ends are connected together, and a capacitor C is also connected between the input terminals IN+ and IN- of the current monitor SQ52201. 34 The SCL and SDA ports of the current monitor SQ52201 are connected to the control circuit to control the current monitor SQ52201 to complete the current measurement and detect the current magnitude when there is a load in real time.

[0048] The control circuit includes an ARM microcontroller STM32F407ZGT6 and peripheral circuits, such as... Figure 9 As shown, the PID feedback regulation method for excitation voltage is based on a position-type + anti-integral saturation + integral separation PID algorithm. The control circuit collects the PVO and NVO port voltages in the excitation voltage drive circuit, sets the excitation voltage value that the PID needs to regulate, and continuously adjusts the input value of the digital-to-analog converter in the programmable excitation reference circuit according to the feedback values ​​of the PVO and NVO ports. A certain number of adjustments are set so that the excitation voltage value at both ends of the strain gauge bridge continuously approaches the set excitation voltage value, thus obtaining a high-precision excitation voltage at both ends of the strain gauge bridge.

[0049] like Figure 10 As shown, the simulation waveform represents the simulated transmission line resistance R under ideal conditions. 42 R 43The resistance is 0Ω, the excitation voltage is set to ±2.5V, the positive excitation voltage output by the excitation voltage drive circuit is VP2, the negative excitation voltage is NV2, PVO is the positive excitation voltage value at the strain gauge bridge terminal, NVO is the negative excitation voltage value at the strain gauge bridge terminal, VP1 is the supply voltage of LT3045, and VN1 is the supply voltage of LT3094. Under ideal conditions, since the transmission line resistance is 0Ω, a long transmission line will not generate a voltage drop, and the excitation voltage across the strain gauge bridge will be equal to the excitation voltage output by the excitation voltage drive circuit module. At the same time, the excitation voltage across the strain gauge bridge is equal to the set excitation voltage, and the difference between VP1 and VP2, and the difference between VN1 and VN2 are fixed at about 1V. It can be seen that the simulation results are consistent with the analysis, and this circuit can improve the conversion efficiency of LT3045 and LT3094.

[0050] like Figure 11 As shown, the simulation waveform is based on the actual situation, assuming the simulated transmission line resistance R... 42 R 43 The resistance is 100Ω, the excitation voltage is set to ±2.5V, the positive excitation voltage output by the excitation voltage drive circuit is VP2, the negative excitation voltage is NV2, PVO is the positive excitation voltage value at the strain gauge bridge terminal, NVO is the negative excitation voltage value at the strain gauge bridge terminal, VP1 is the power supply voltage of LT3045, and VN1 is the power supply voltage of LT3094. In actual conditions, due to the influence of transmission line resistance, a voltage drop will occur over a long transmission line, causing the excitation voltage at both ends of the strain gauge bridge to be lower than the excitation voltage output by the excitation voltage drive circuit module. At the same time, the excitation voltage at both ends of the strain gauge bridge is equal to the set excitation voltage, and the difference between VP1 and VP2, and the difference between VN1 and VN2 are fixed at about 1V. It can be seen that this circuit can both compensate for the voltage drop caused by the transmission line and improve the conversion efficiency of LT3045 and LT3094.

[0051] In the specific implementation process, it is necessary to clarify the length of the compensable transmission line. The maximum output voltage of the switching regulator LT3045 is 15V, and the maximum output voltage of the switching regulator LT304594 is -15V. To ensure that the positive and negative excitation voltage values ​​are equal, the maximum output of the positive and negative excitation voltages of the excitation voltage drive circuit module is V = VP2 - VN2 = 15V + 15V = 30V. According to Ohm's law, V = V 设 / R S ×(2×R L )+V 设 V 设 R is the set bridge excitation voltage; S R is the resistance value of the full-bridge resistance strain gauge; L Let R be the resistance of the transmission line. S =350Ω, V 设 =20V, so R can be obtainedL =87Ω, then the transmission line resistance that can be compensated when the excitation voltage is at its maximum value is 87Ω. If the strain gauge bridge uses a network cable as the transmission line, the resistance of a 100-meter network cable is about 15Ω. Then the longest compensable transmission line length is 580 meters, which is far sufficient for the test distance. Moreover, when the excitation voltage is lower than the maximum excitation voltage, the compensable transmission line distance is even longer.

[0052] This invention discloses a high-precision programmable strain gauge bridge excitation source, which ultimately provides a high-precision adjustable excitation voltage for use in a strain gauge bridge. The achievable measurement range is -10V to +10V, with a measurement accuracy better than (0.012% SET + 2mV). Compared to existing excitation sources, this source offers higher accuracy, a wider excitation voltage range, and broader applicability. It is programmable and suitable for most strain signal acquisition-related equipment and instruments, rather than being limited to a specific project, thus offering better versatility. The programmable excitation voltage can meet most of the excitation voltage requirements of strain gauge sensors on the market, indirectly improving the accuracy of strain measurement.

[0053] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high-precision, programmable strain gauge bridge excitation source, characterized in that: It includes a reference reference source circuit, a programmable excitation reference circuit, an excitation reference amplifier circuit, an excitation voltage drive circuit, and a control circuit. The reference reference source circuit outputs a reference voltage to the programmable excitation reference circuit. The control circuit controls the positive and negative excitation reference voltages output by the programmable excitation reference circuit to be amplified, buffered, and flipped by the excitation reference amplifier circuit to generate positive and negative excitation voltages. The excitation voltage drive circuit drives the positive and negative excitation voltages and outputs them to the strain gauge bridge, while automatically feeding back and compensating for the voltage drop of the excitation voltage applied to the strain gauge bridge. The reference source circuit includes a voltage reference chip REF5025 and an operational amplifier OPA333. The input of the operational amplifier OPA333 is connected to the output of the voltage reference chip REF5025, acting as a voltage follower with an RC low-pass filter. The programmable excitation reference circuit includes a digital-to-analog converter DAC8552 and peripheral circuitry. Port VREF of the DAC8552 is connected to port VREF of the reference source circuit. Ports DADIN, DASCLK, and DASYNC of the DAC8552 are connected to the control circuit. Port V of the DAC8552... Out A and V Out B outputs positive and negative excitation reference voltages respectively; the excitation reference amplifier circuit includes positive and negative reference voltage amplifier circuits composed of an instrumentation amplifier INA819 and peripheral circuits. The non-inverting input of the instrumentation amplifier INA819 in the positive reference voltage amplifier circuit outputs V... Out The positive excitation reference voltage output by A is passed through an external resistor R. 17 Amplify and output the positive excitation voltage from the PV port. The non-inverting input of the instrumentation amplifier INA819 in the negative reference voltage amplifier circuit will amplify and output the positive excitation voltage. Out The negative excitation reference voltage output by B is passed through an external resistor R. 20 Amplify and output the negative excitation voltage from the NV port; The excitation voltage drive circuit is divided into positive and negative excitation voltage drive circuits. The positive excitation voltage drive circuit includes a switching regulator LT8608, an operational amplifier LT1678, a programmable linear regulator LT3045, and peripheral circuitry. Port PVI of the programmable linear regulator LT3045 is connected to the output port PV of the positive reference voltage amplifier circuit. The positive excitation voltage is output from port VP2 of the programmable linear regulator LT3045. The output interface of port VP2 of the programmable linear regulator LT3045 is EX+, which is connected through a resistor R. 42 The transmission line provides a positive excitation voltage to the A terminal of the strain gauge bridge. The interface connected to the port PVO of the programmable linear regulator LT3045 is EXS+. The EXS+ interface is directly connected to the A terminal of the strain gauge bridge. The actual excitation voltage across the strain gauge bridge can be fed back to the port PVO through the EXS+ interface, which increases the excitation voltage VP2 output by the programmable linear regulator LT3045. When it reaches the A terminal of the strain gauge bridge through the transmission line, VP2 drops to the actual set positive excitation voltage. The negative excitation voltage drive circuit includes a switching regulator LT8330, an operational amplifier LT1678, a programmable linear regulator LT3094, and peripheral circuitry. Port NVI of the programmable linear regulator LT3094 is connected to the output port NV of the negative reference voltage amplifier circuit. The negative excitation voltage is output from port VN2 of the programmable linear regulator LT3094. The output interface of port VN2 of the programmable linear regulator LT3094 is EX-, connected via a resistor R. 43 The transmission line provides a negative excitation voltage to the strain gauge bridge. The interface connected to port NVO of the programmable linear regulator LT3094 is EXS-. The EXS- interface is directly connected to the C terminal of the strain gauge bridge. The actual excitation voltage across the strain gauge bridge can be fed back to port NVO through the EXS- interface, which increases the excitation voltage VN2 output by LT3045. When VN2 reaches the C terminal of the strain gauge bridge through the transmission line, it drops to the actual set negative excitation voltage.

2. The high-precision programmable strain bridge excitation source according to claim 1, characterized in that: A self-feedback supply voltage circuit for a linear regulator is provided between the switching regulator LT8608 and the operational amplifier LT1678 in the positive excitation voltage drive circuit. The switching regulator LT8608 adjusts the feedback pin FB to the first value. According to the voltage divider principle of resistors R22 and R23, the output voltage of the operational amplifier LT1678 is clamped to the second value. The negative input terminal of the operational amplifier is the positive excitation voltage VP2, and the positive input terminal is the supply voltage VP1 of LT3045. The supply voltage VP1 is automatically adjusted according to the positive excitation voltage VP2 so that the difference between VP2 and VP1 is always equal to the second value.

3. The high-precision programmable strain bridge excitation source according to claim 1, characterized in that: A self-feedback supply voltage circuit for a linear regulator is provided between the switching regulator LT8830 and the operational amplifier LT1678 in the negative excitation voltage drive circuit. The switching regulator LT8830 adjusts the feedback pin FB to the first value. According to the voltage divider principle of resistors R29 and R30, the output voltage of the operational amplifier LT1678 is clamped to the second value. The negative input terminal of the operational amplifier is the negative excitation voltage VN2, and the positive input terminal is the supply voltage VN1 of LT3094. The supply voltage VN1 is automatically adjusted according to the negative excitation voltage VN2 so that the difference between VN2 and VN1 is always equal to the second value.

4. A high-precision programmable strain bridge excitation source according to claim 2 or 3, characterized in that: The first value is 0.778V, and the second value is 1V.

5. A high-precision programmable strain bridge excitation source according to claim 4, characterized in that: It also includes a current monitoring circuit, which consists of a current monitor SQ52201 and a programmable linear regulator LT3045. The positive excitation voltage VP2 output by VP2 provides positive excitation to the strain gauge bridge through the EX+ interface. A resistor R is connected in series between VP2 and EX+. 36 The input terminals IN+ and IN- of the current monitor SQ52201 are respectively connected to resistor R. 37 Resistance R 38 With resistance R 36 The two ends are connected together, and a capacitor C is also connected between the input terminals IN+ and IN- of the current monitor SQ52201. 34 The SCL and SDA ports of the current monitor SQ52201 are connected to the control circuit to control the current monitor SQ52201 to complete the current measurement and detect the current magnitude when there is a load in real time.

6. The high-precision programmable strain bridge excitation source according to claim 5, characterized in that: The control circuit includes an ARM microcontroller STM32F407ZGT6 and peripheral circuits. The control circuit acquires the PVO and NVO port voltages in the excitation voltage drive circuit, sets the excitation voltage value that the PID controller needs to adjust, and continuously adjusts the input value of the digital-to-analog converter in the programmable excitation reference circuit based on the feedback values ​​of the PVO and NVO ports, so that the excitation voltage value at both ends of the strain gauge bridge continuously approaches the set excitation voltage value, thereby obtaining a high-precision excitation voltage at both ends of the strain gauge bridge.

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