Temperature Drift Inhibition Circuit for the Bridge Sensor of the Silk Thread Tensiometer

Abstract

The present invention relates to the technical field of wire tension sensors, and particularly to a temperature drift suppression circuit for a bridge-type sensor of a wire tensiometer. It includes a full-bridge circuit, and the full-bridge circuit includes four strain resistors R1-R4 each having basically the same properties. One strain resistor is placed in each arm of the full-bridge circuit. There are a first input point A, a second input point B, a first output point C, and a second output point D provided on the full-bridge circuit. It also includes a power supply, and the positive and negative poles of the power supply are respectively connected to the first input point A and the second input point B. It further includes a fixed-value resistor R7, a thermistor R8, and a proportional resistor R9. One end of the fixed-value resistor R7 is connected to the first input point A, and the other end is simultaneously connected to the thermistor R8 and the proportional resistor R9. The other end of the thermistor R8 is connected to the second input point B, and the other end of the proportional resistor R9 is connected to one of the second output point D or the first output point C. The present invention can effectively suppress the temperature drift of the bridge-type sensor.

Description

Technical Field

[0001] The present invention relates to the technical field of wire tension sensors, and particularly to a temperature drift suppression circuit for a bridge sensor of a wire tensiometer. Background Art

[0002] During the wire processing, the wire tension is a very important parameter. The magnitude and stability of the tension are directly related to the product quality, production efficiency, and the smooth progress of subsequent processing. The wire tension detection system is a device used to measure the wire tension. It consists of a wire tensiometer, an amplifier circuit, a data acquisition circuit, and system software. The tension sensor is installed on the wire path of the wire. The wire tension is converted into an electrical signal through a transducer element. At this time, the output electrical signal is very weak and requires a dedicated amplifier circuit to amplify and preliminarily filter these weak signals to reduce noise interference. In order to analyze and process the wire tension signal using a microprocessor or computer, the voltage signal output from the amplifier circuit needs to be converted from analog to digital. Since there are usually many wire paths in general textile machinery and the number of spindle positions is usually around several hundred, the data acquisition circuit also needs to coordinate the acquisition of the wire tension signal. After the data acquisition circuit completes the digitization of the analog quantity and further processing of the signal, it uploads the digital signal to the upper computer. At this time, the system software on the upper computer will complete the real-time display, analysis, and storage of the wire tension signal.

[0003] In a false twist device, the wire tensiometer is a resistance strain type tensiometer, and its structural principle is as Figure 1-2 shown. Four strain resistors R1 - R4 are pasted on the upper and lower surfaces of the cantilever beam to form a full bridge circuit. The wire tension is converted into the pressure F on the middle roller 2 by using three rollers, and the force is then transmitted to the cantilever beam through a force transmission block. The cantilever beam generates a strain proportional to the tension accordingly. This strain is converted into a change in resistance, and then the change in resistance is converted into a change in electrical quantity through a bridge circuit. After calibration, it is fed to the subsequent signal processing device. By analyzing the signal, the wire tension and its change information can be obtained. The full bridge circuit is as Figure 3 shown. Due to various reasons, when the input measured quantity is zero, its output is not zero, that is, there is zero drift. The reason is that there are certain deviations in the strain resistors of each bridge arm of the sensor, making the bridge unbalanced, that is, R1*R4≠R2*R3, and there is a zero point U0 output. A zero adjustment circuit needs to be added to the full bridge circuit to solve the above problem. The bridge sensor circuit is as Figure 4 shown. By adjusting R5 in R wThe position is such that the voltage difference between positions B and D is zero. Since all conductors have a temperature coefficient, their resistance values increase as the temperature rises. For example, the temperature coefficient of a commonly used metal film resistor is around 300 ppm, that is, for every 1°C increase, its resistance value increases by three ten-thousandths. This numerical change has little impact on ordinary application scenarios but can cause huge errors in a full-bridge circuit. Due to manufacturing process problems, there are also slight differences in the temperature coefficients of the strain resistors on the full-bridge circuit. When the temperature changes, the change rates of the four strain resistors are not exactly the same, resulting in zero drift. For example, when the tension is zero, at 20°C, U0 is equal to zero. When the temperature rises to 30°C, due to the influence of temperature, U0 is not equal to zero. This phenomenon is called temperature drift, which makes the value of U0 unable to fully reflect the change in tension, resulting in the calculated tension value not matching the actual value in subsequent calculations. Summary of the Invention

[0004] The technical problem to be solved by the present invention is, in view of the above-mentioned existing technical deficiencies, to provide a temperature drift suppression circuit for a bridge sensor of a silk thread tensiometer, which can suppress the temperature drift of the bridge sensor.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is: a temperature drift suppression circuit for a bridge sensor of a silk thread tensiometer, including a full-bridge circuit. The full-bridge circuit includes four strain resistors R1 - R4 each having basically the same properties. One strain resistor is placed in each bridge arm of the full-bridge circuit. There are a first input point A, a second input point B, a first output point C, and a second output point D on the full-bridge circuit. It also includes a power supply, the positive and negative poles of the power supply are respectively connected to the first input point A and the second input point B. It also includes a fixed-value resistor R7, a thermistor R8, and a proportional resistor R9. One end of the fixed-value resistor R7 is connected to the first input point A, and the other end is simultaneously connected to the thermistor R8 and the proportional resistor R9. The other end of the thermistor R8 is connected to the second input point B, and the other end of the proportional resistor R9 is connected to one of the second output point D or the first output point C.

[0006] To further optimize the technical solution, this circuit also includes a potentiometer R w and an adjustment resistor R5. The two fixed ends of the potentiometer R w are respectively connected to the first input point A and the second input point B. One end of the resistor R5 is connected to the second output point D, and the other end is connected to the sliding contact lead-out end of the potentiometer R w .

[0007] A method for determining the resistance value of the proportional resistor R9 in a temperature drift suppression circuit for a bridge sensor of a silk thread tensiometer, characterized by including the steps:

[0008] S1. Replace the proportional resistor R9 with a digital potentiometer and connect it to the temperature drift suppression circuit of the silk thread tension gauge bridge sensor. Disconnect the connection between the digital potentiometer and the second output point D. At room temperature, adjust the resistance value of the potentiometer R w to make the potential difference between the first output point C and the second output point D zero;

[0009] S2. Heat the entire circuit (excluding the power supply) and check whether the potential difference between the first output point C and the second output point D is positive or negative.

[0010] S3. In the case where the thermistor R8 is a negative temperature coefficient thermistor, when the potential difference between the first output point C and the second output point D is positive, connect the other end of the digital potentiometer to the second output point D; when the potential difference between the first output point C and the second output point D is negative, connect the other end of the digital potentiometer to the first output point C. In the case where the thermistor R8 is a positive temperature coefficient thermistor, when the potential difference between the first output point C and the second output point D is negative, connect the other end of the digital potentiometer to the second output point D; when the potential difference between the first output point C and the second output point D is positive, connect the other end of the digital potentiometer to the first output point C.

[0011] S4. Set the entire circuit to 20°C, make the digital potentiometer output multiple resistances in an arithmetic progression respectively, measure the output voltage corresponding to each resistance respectively and record it;

[0012] S5. Set the entire circuit to 50°C, make the digital potentiometer output multiple resistances in the same arithmetic progression as in step S4 respectively, measure the output voltage corresponding to each resistance respectively and record it;

[0013] S6. Calculate the difference in the output voltage corresponding to each resistance at 20°C and 50°C, and find the two adjacent resistance values corresponding to the smallest two differences;

[0014] S7. Divide the values between the two adjacent resistance values obtained in step S6 into resistances with multiple resistance values in an arithmetic progression, and then repeat steps S4 - S6, noting that the digital potentiometer outputs the multiple resistance values obtained in this step;

[0015] S8. Keep repeating step S7 until the value of the temperature drift meets the requirements.

[0016] S9. Remove the digital potentiometer and replace it with a proportional resistor R9 with the resistance value obtained in step S8 and connect it to the circuit.

[0017] Compared with the prior art, the present invention has the following advantages: 1. The resistance value of the thermistor changes with temperature, which causes the voltage division to change. The proportional resistor with an appropriate resistance value can make the influence brought by the thermistor close to and opposite in sign to the influence of the temperature drift of the full-bridge circuit, thus making it possible to control the temperature drift of the bridge sensor within an acceptable range; 2. It is possible to determine the value of the proportional resistor in a certain bridge sensor according to the actual situation, so that the value of the proportional resistor in the circuit can be more appropriate. Description of the Drawings

[0018] Figure 1 It is a schematic diagram showing the distribution of strain resistors on the cantilever beam.

[0019] Figure 2 It is a schematic diagram showing the principle of force and deformation of the cantilever beam.

[0020] Figure 3 It is a schematic diagram of the full-bridge circuit in the prior art.

[0021] Figure 4 It is a schematic diagram of the bridge sensor circuit in the prior art.

[0022] Figure 5 It is a schematic diagram of the bridge sensor circuit of the present invention.

[0023] Figure 6 It is a schematic diagram of the circuit when determining the resistance value of the proportional resistor R9 of the present invention.

[0024] Figure 7 It is a schematic diagram of the temperature drift data curve without a temperature drift suppression circuit.

[0025] Figure 8 It is a schematic diagram of the suppression effect data curve of the temperature drift suppression circuit.

[0026] Figure 9 It is a schematic diagram of the principle of the combined effect of the temperature drift effect and the temperature drift suppression circuit.

[0027] Figure 10 It is a schematic diagram of the principle of the deviation between the temperature drift suppression effect and the actual value. Detailed Embodiments

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0029] Embodiment 1

[0030] Temperature drift suppression circuit for the bridge sensor of a silk thread tension meter, including a full-bridge circuit. The full-bridge circuit includes four strain resistors R1 - R4 with basically the same properties (i.e., their technical indicators are the same, but due to manufacturing process problems, there will be slight differences among them). One strain resistor is placed in each arm of the full-bridge circuit. There are a first input point A, a second input point B, a first output point C, and a second output point D on the full-bridge circuit. It also includes a power supply, the positive and negative poles of the power supply are respectively connected to the first input point A and the second input point B. It further includes a fixed resistor R7, a thermistor R8, and a proportional resistor R9. One end of the fixed resistor R7 is connected to the first input point A, and the other end is simultaneously connected to the thermistor R8 and the proportional resistor R9. The other end of the thermistor R8 is connected to the second input point B, and the other end of the proportional resistor R9 is connected to one of the second output point D or the first output point C. When the resistance value of the proportional resistor R9 is appropriate, the temperature drift can be small to an acceptable range, such as about 20 mV. In the actual situation of the silk thread tension meter bridge sensor, the resistance values of R1 - R4 are all about 650 Ω. Preferably, the resistance value of the fixed resistor R7 is 10 kΩ, and the thermistor R8 is a model with a resistance value of 10 kΩ at 25 °C, such as NCP18XH103F03RB, with a B value of 3380 (in the range of 25 °C - 50 °C), a resistance value of 12.081 kΩ at 20 °C, 10 kΩ at 25 °C, 8.315 kΩ at 30 °C, 6.948 kΩ at 35 °C, 5.834 kΩ at 40 °C, 4.917 kΩ at 45 °C, and 4.161 kΩ at 50 °C.

[0031] The principle of temperature drift suppression in this circuit is as follows: Assume that the temperature drift coefficient of R4 is 4 ppm, the resistance is 468 Ω at 20 °C, and it becomes 468.0019 when it rises to 50 °C. After being amplified and output by the amplifier circuit, the temperature drift can reach +333 mV. The method of temperature compensation is that when the temperature rises from 20 °C to 50 °C, the temperature drift suppression circuit makes R4 generate a drift close to -333 mV at the same time, so that the total value of the temperature drift is small to an acceptable range. As Figure 7 shown, when there is no temperature drift suppression circuit, the data curve of the temperature drift is linear. As Figure 8 shown, the data curve of the suppression effect of the temperature drift suppression circuit is close to linear. By adjusting the resistance value of the proportional resistor R9, the slope of this curve can be adjusted. As Figure 9 shown, when the slope of this straight line is very close to the slope of this curve, the sum of the two is close to zero at any temperature (in the range of 20 °C - 50 °C). Figure 9 Above "0" V is positive, and below "0" V is negative. That is, as long as the resistance value of the proportional resistor R9 is appropriate, the absolute values of the two at each temperature point can be very close and opposite in sign, so that the overall temperature drift is close to zero or greatly reduced.

[0032] Example 2

[0033] Based on Example 1, the circuit of this example further includes a potentiometer R w and an adjusting resistor R5. Two fixed ends of the potentiometer R w are respectively connected to a first input point A and a second input point B. One end of the adjusting resistor R5 is connected to a second output point D, and the other end is connected to a sliding contact lead-out end of the potentiometer R w . By adjusting the resistance value of the potentiometer R w , the zero point of the circuit can be adjusted. In terms of the actual situation of the silk thread tension gauge bridge sensor, it is preferred that the potentiometer R w adopts a potentiometer with a maximum value of 50 kΩ, and the resistance value of the adjusting resistor R5 is 3.01 MΩ.

[0034] Example 3

[0035] A method for determining the resistance value of the proportional resistor R9 in the above-mentioned silk thread tension gauge bridge sensor temperature drift suppression circuit, which is characterized by including the steps of:

[0036] S1. Replace R9 with a digital potentiometer and connect it to the silk thread tension gauge bridge sensor temperature drift suppression circuit, and disconnect the connection between the digital potentiometer and the second output point D. At room temperature (any temperature within 20°C - 50°C), adjust the resistance value of the potentiometer R w to make the potential difference between the first output point C and the second output point D zero;

[0037] S2. Heat the entire circuit and check whether the potential difference between the first output point C and the second output point D is positive or negative.

[0038] S3. In the case where the thermistor R8 is a negative temperature coefficient thermistor, when the potential difference between the first output point C and the second output point D is positive, the other end of the digital potentiometer is connected to the second output point D; when the potential difference between the first output point C and the second output point D is negative, the other end of the digital potentiometer is connected to the first output point C. In the case where the thermistor R8 is a positive temperature coefficient thermistor, when the potential difference between the first output point C and the second output point D is negative, the other end of the digital potentiometer is connected to the second output point D; when the potential difference between the first output point C and the second output point D is positive, the other end of the digital potentiometer is connected to the first output point C.

[0039] S4. Keep the entire circuit at 20°C, control the digital potentiometer to make the digital potentiometer output 10 kinds of resistances of 1 MΩ, 2 MΩ, 3 MΩ, 4 MΩ, 5 MΩ, 6 MΩ, 7 MΩ, 8 MΩ, 9 MΩ, and 10 MΩ respectively, and measure and record the corresponding output voltages (the potential difference between the first output point C and the second output point D, the same below);

[0040] S5. Set the entire circuit to 50°C, control the digital potentiometer to output ten resistances of 1 MΩ, 2 MΩ, 3 MΩ, 4 MΩ, 5 MΩ, 6 MΩ, 7 MΩ, 8 MΩ, 9 MΩ, and 10 MΩ respectively, and measure and record the output voltage corresponding to each resistance.

[0041] S6. Calculate the difference in the output voltage corresponding to each resistance at 20°C and 50°C, and find the two adjacent resistance values corresponding to the two smallest differences. For example, when determining the resistance value of the proportional resistor R9 in a temperature drift suppression circuit of a certain wire tension gauge bridge sensor, the measured data is shown in the following table (a 1V bias voltage is added after amplification by the amplifier circuit):

[0042]

[0043]

[0044] It can be found that the two adjacent resistance values corresponding to the two smallest differences are 6 MΩ and 7 MΩ.

[0045] S7. Divide the values between the two adjacent resistance values obtained in step S6 into resistances of multiple values in an arithmetic progression, and then repeat steps S4 - S6, noting that the digital potentiometer outputs the resistances of multiple values obtained in this step. Continuing with the example in step S6, for example, the digital potentiometer can be made to output nine resistances of 6.1 MΩ, 6.2 MΩ, 6.3 MΩ, 6.4 MΩ, 6.5 MΩ, 6.6 MΩ, 6.7 MΩ, 6.8 MΩ, and 6.9 MΩ respectively, and measure and record the corresponding output voltages; then set the entire circuit to 50°C, control the digital potentiometer to output nine resistances of 6.1 MΩ, 6.2 MΩ, 6.3 MΩ, 6.4 MΩ, 6.5 MΩ, 6.6 MΩ, 6.7 MΩ, 6.8 MΩ, and 6.9 MΩ respectively, and measure and record the output voltage corresponding to each resistance. The measured data is shown in the following table (a 1V bias voltage is added after amplification by the amplifier circuit):

[0046] 6.1 MΩ 6.2 MΩ 6.3 MΩ 6.4 MΩ 6.5 MΩ 6.6 MΩ 6.7 MΩ 6.8 MΩ 6.9 MΩ Output Voltage (V) at 20°C 1.037 1.033 1.031 1.028 1.026 1.024 1.021 1.019 1.015 Output Voltage (V) at 50°C 1.028 1.027 1.026 1.025 1.024 1.023 1.022 1.021 1.018 Voltage Difference (V) +0.009 +0.006 +0.005 +0.003 +0.002 +0.001 -0.001 -0.002 -0.003

[0047] It can be found that the two adjacent resistance values corresponding to the smallest two differences are 6.6 MΩ and 6.7 MΩ. At the same time, it can be seen that the output voltage at 20°C is greater than the output voltage at 50°C for the resistance values of 6.6 MΩ and those before it (less than 6.6 MΩ), and the output voltage at 20°C is less than the output voltage at 50°C for the resistance values of 6.7 MΩ and those after it (greater than 6.7 MΩ). If the data at each temperature for each resistance value is regarded as an approximately straight line (with the resistance value as the ordinate and the temperature as the abscissa), between 6.6 MΩ and 6.7 MΩ is the watershed for the positive and negative slopes of this approximately straight line, which indicates that the optimal resistance value is between 6.6 MΩ and 6.7 MΩ. The same is true for the data corresponding to 6 MΩ and 7 MΩ in the previous table.

[0048] S8. Generally speaking, the above resistance values can already meet the requirements. If higher precision is pursued, the values between the two adjacent resistance values obtained in step S7 can be divided into resistances with multiple resistance values according to an arithmetic progression, and then steps S4 - S6 are repeated. Note that the digital potentiometer outputs the resistances with multiple resistance values obtained in this step, and so on until the temperature drift value obtained meets the requirements.

[0049] S9. Remove the digital potentiometer, and replace the digital potentiometer in the circuit with a proportional resistor R9 whose resistance value is the value obtained in step S8 (any one of the two values, or any one within the range of the two values) to obtain the circuit in Embodiment 1 or Embodiment 2.

[0050] Figure 10 is a schematic diagram of the curve of the output voltage when the input is zero at each temperature for the circuit obtained in step S9 (the output voltage is added with a bias voltage of 1V after being amplified by the amplifier circuit). Through Figure 10 it can be seen that since the input is zero, the true value of the output voltage should be 1V. However, the actual output voltage value shows a certain curve (the degree of bending of this curve is caused by the non - linear characteristics of the thermistor, which has a certain impact on suppressing temperature drift, so the properties of the thermistor are very important. Generally speaking, the smaller the B value, the better), and the two ends and the middle of this curve are respectively on both sides of 1V, making the actual output voltage value as close as possible to the true output voltage. At this time, the maximum value of the difference between this curve and the straight line of 1V is much smaller than the temperature drift value without the temperature drift suppression circuit.

[0051] Currently, high - precision strain resistors are monopolized by American companies such as VMM, VISHAY, and German company HBM. The consistency of domestic strain resistors is relatively low and generally cannot be used in wire tension meters. With the temperature drift suppression circuit for the wire tension meter bridge sensor and the method for determining the resistance value of the proportional resistor R9 in this application, even if domestic strain resistors (resistive strain gauges) are used, the accuracy and performance of the tension sensor can reach the imported standards in most cases.

Claims

1. Temperature drift suppression circuit for the bridge sensor of a silk thread tensiometer, including a full-bridge circuit. The full-bridge circuit includes four strain resistors R1-R4 with basically the same properties. One strain resistor is placed in each arm of the full-bridge circuit. The full-bridge circuit is provided with a first input point A, a second input point B, a first output point C, and a second output point D. The first input point A and the second input point B are respectively used to connect the positive and negative poles of a DC power supply, and it is characterized in that: It also includes a fixed resistor R7, a thermistor R8 and a proportional resistor R9. One end of the fixed resistor R7 is connected to the first input point A, and the other end is simultaneously connected to the thermistor R8 and the proportional resistor R9. The other end of the thermistor R8 is connected to the second input point B, and the other end of the proportional resistor R9 is connected to one of the second output point D or the first output point C. It also includes a potentiometer R w and an adjusting resistor R5. The two fixed ends of the potentiometer R w are respectively connected to the first input point A and the second input point B. One end of the adjusting resistor R5 is connected to the second output point D, and the other end is connected to the sliding contact lead-out end of the potentiometer R w ; wherein, the method for determining the resistance value of the proportional resistor R9 includes the following steps: S1. Replace the proportional resistor R9 with a digital potentiometer and connect it to the temperature drift suppression circuit of the silk tension gauge bridge sensor. Disconnect the connection between the digital potentiometer and the second output point D. At room temperature, adjust the resistance value of the potentiometer Rw to make the potential difference between the first output point C and the second output point D zero; S2. Heat the entire circuit and check whether the potential difference between the first output point C and the second output point D is positive or negative; S3. When the thermistor R8 is a negative temperature coefficient thermistor, when the potential difference between the first output point C and the second output point D is positive, connect the other end of the digital potentiometer to the second output point D. When the potential difference between the first output point C and the second output point D is negative, connect the other end of the digital potentiometer to the first output point C. When the thermistor R8 is a positive temperature coefficient thermistor, when the potential difference between the first output point C and the second output point D is negative, connect the other end of the digital potentiometer to the second output point D. When the potential difference between the first output point C and the second output point D is positive, connect the other end of the digital potentiometer to the first output point C; S4. Set the entire circuit to 20°C, make the digital potentiometer output multiple resistances in an arithmetic progression, and measure and record the output voltage corresponding to each resistance respectively; S5. Set the entire circuit to 50°C, make the digital potentiometer output multiple resistances in the same arithmetic progression as in step S4, and measure and record the output voltage corresponding to each resistance respectively; S6. Calculate the difference in the output voltage corresponding to each resistance at 20°C and 50°C, and find the two adjacent resistance values corresponding to the smallest two differences; S7. Divide the values between the two adjacent resistance values obtained in step S6 into resistances of multiple values in an arithmetic progression, and then repeat steps S4 - S6, noting that the digital potentiometer outputs the multiple resistance values obtained in this step; S8. Divide the values between the two adjacent resistance values obtained in step S7 into resistances of multiple values in an arithmetic progression, and then repeat steps S4 - S6, noting that the digital potentiometer outputs the multiple resistance values obtained in this step. And so on until the obtained temperature drift value meets the requirements; S9. Remove the digital potentiometer and replace it with a proportional resistor R9 with a resistance value obtained in step S8 and connect it to the circuit.

Images