A circuit for measuring the tiny resistance of polyethylene electric fusion pipe fittings

Abstract

The present invention discloses a circuit for measuring the tiny resistance of polyethylene electric fusion pipe fittings, including a main control chip, a current expansion circuit, a series resistance circuit and a parallel resistance circuit; the output end of the main control chip is connected to the in-phase input end of the first operational amplifier U1 to provide a voltage output signal; the inverting input end of the first operational amplifier U1 is connected to the connecting line between the third resistor R3 and the fourth resistor R4; the emitter end of the triode T1 is connected to the first connection end V1 of the parallel resistance circuit, and the third connection end V3 is arranged on the connecting line between the fourth resistor R4 and the fifth resistor R5, and the three input ends of the main control chip respectively collect the voltage values ​​of three test points. Beneficial effects of the present invention: the measurement range of the measurement circuit of the present invention is 0.1Ω-10Ω, which basically meets the measurement of the resistance value of all types of electric fusion pipe fittings, and has the characteristics of high measurement accuracy and accurate measurement, thereby improving the welding quality of polyethylene pipes.

Description

Technical Field

[0001] The invention belongs to the technical field of electric fusion welding, and in particular relates to a circuit for measuring the minute resistance of a polyethylene electric fusion pipe fitting. Background Art

[0002] Polyethylene pipes have the advantages of high strength, durability, corrosion resistance, low production and installation cost, and easy connection. They are widely used in gas transportation, water supply, oil fields, etc. The reliability of polyethylene pipe connection is a key factor affecting the installation quality and service life of the pipe. Electric fusion welding is one of the main methods of polyethylene pipe welding due to its advantages of simple operation, fast welding speed, and high welding quality.

[0003] The basic principle of electric fusion welding is to put the electric fusion pipe joint with embedded resistance wire on the pipe, and then pass a certain intensity of current. The resistance wire heats up to melt the connecting part between the pipe joint and the pipe. Under the action of the molten expansion pressure, the resin molecules on both sides of the connection interface are re-entangled, and the connection purpose is achieved after cooling.

[0004] According to the principle of electric fusion welding and domestic and foreign practical experience, whether polyethylene pipes can form reliable welding connections is closely related to the design of electric fusion pipe fittings, the resistance value of the pre-embedded resistance wire in the electric fusion pipe fittings, the welding voltage provided by the electric fusion welding machine, welding process parameters and other factors. Moreover, the welding voltage output by the electric fusion welding machine is calculated based on the resistance value of the electric fusion pipe fittings. Therefore, the measurement of the resistance value of the pre-embedded resistance wire in the electric fusion pipe fittings is crucial.

[0005] Ordinary electric fusion welding machines use a manual handheld card reader to scan and read the parameters of the pipe fittings. However, the diameter and length of the resistance wire embedded in the electric fusion pipe fittings determine the different resistance values. In addition, the resistance value itself will also change due to the influence of ambient temperature and the use time of the equipment. Since the resistance value of the resistance wire embedded in the electric fusion pipe fittings cannot be accurately measured, the precise output voltage of the electric fusion welding machine cannot be determined, which affects the welding quality. Summary of the invention

[0006] Aiming at the problem that the resistance of the embedded resistance wire in the electric fusion pipe fitting cannot be accurately measured in the prior art, the precise output voltage of the electric fusion welding machine cannot be determined, and the welding quality is affected, a polyethylene electric fusion pipe fitting micro-resistance measurement circuit is provided. The electric fusion pipe fitting to be measured is connected to the measurement circuit, and the resistance of the electric fusion pipe fitting can be automatically measured. By measuring the resistance of each electric fusion pipe fitting, the welding voltage output of the electric fusion welding machine is more accurate and the welding quality is higher.

[0007] The technical solution adopted by the present invention is:

[0008] A circuit for measuring the tiny resistance of a polyethylene electric fusion pipe, comprising a main control chip, a current expansion circuit, a series resistance circuit and a parallel resistance circuit;

[0009] The current expansion circuit includes a first operational amplifier U1, a second operational amplifier U2 and a transistor T1, the output end of the first operational amplifier U1 is electrically connected to the in-phase input end of the second operational amplifier U2, the negative power supply end of the second operational amplifier U2 is grounded, the positive power supply end of the second operational amplifier U2 is connected to the positive electrode of the DC power supply, the output end of the second operational amplifier U2 is connected to the base end of the transistor T1, the inverting input end of the second operational amplifier U2 is electrically connected to the connecting line between its output end and the base end of the transistor T1, and the collector end of the transistor T1 is connected to the positive electrode of the DC power supply;

[0010] The series resistor circuit is formed by connecting a third resistor R3, a fourth resistor R4 and a fifth resistor R5 in series in sequence, the other end of the third resistor R3 is grounded, and the other end of the fifth resistor R5 is grounded;

[0011] The parallel resistor circuit includes a first connection terminal V1, a second connection terminal V2, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9 and a tenth resistor R10, one end of each of the sixth resistor R6, the seventh resistor R7, the eighth resistor R8, the ninth resistor R9 and the tenth resistor R10 is connected to the first connection terminal V1, and the other end is connected to the second connection terminal V2;

[0012] The output terminal of the main control chip is connected to the in-phase input terminal of the first operational amplifier U1 to provide a voltage output signal;

[0013] The inverting input terminal of the first operational amplifier U1 is connected to a connecting line between the third resistor R3 and the fourth resistor R4;

[0014] The emitter terminal of the transistor T1 is connected to the first connection terminal V1 of the parallel resistance circuit.

[0015] The third connection terminal V3 is arranged on the connection line between the fourth resistor R4 and the fifth resistor R5.

[0016] The three input terminals of the main control chip are respectively connected to the first connection terminal V1, the second connection terminal V2, and the third connection terminal V3, and the voltage values ​​of the three test points are respectively collected.

[0017] On the basis of the above solution, the first connection terminal V1 is connected to the anode of the first diode D1, and the cathode of the first diode D1 is connected to the positive electrode of the power supply;

[0018] The second connection terminal V2 is connected to the anode of the second diode D2, and the cathode of the second diode D2 is connected to the positive electrode of the power supply;

[0019] The third connection terminal V3 is connected to the anode of the third diode D3, and the cathode of the third diode D3 is connected to the positive electrode of the power supply.

[0020] Preferably, a point on the connection line between the positive power supply terminal of the second operational amplifier U2 and the positive power supply electrode 12V is connected to the fourth capacitor C4, and the other end of the fourth capacitor C4 is grounded.

[0021] Preferably, a second resistor R2 is connected to a connection line between the output end of the main control chip and the in-phase input end of the first operational amplifier U1.

[0022] Preferably, the main control chip is an STM32 chip, the DAC module of which is an output terminal, providing a voltage signal, and the ADC module of which is an input terminal, respectively collecting the voltage values ​​of the first connection terminal V1, the second connection terminal V2, and the third connection terminal V3.

[0023] Preferably, the main control chip is connected to a clock circuit and a reset circuit.

[0024] Preferably, the resistance values ​​of the sixth resistor R6, the seventh resistor R7, the eighth resistor R8, the ninth resistor R9 and the tenth resistor R10 are all 10Ω.

[0025] Beneficial effects of the present invention:

[0026] The measuring circuit of the present invention has a measuring range of 0.1Ω-10Ω, which basically meets the measurement of the resistance values ​​of all types of electric fusion pipe fittings and has the characteristics of high measuring precision and accurate measurement, thereby improving the welding quality of polyethylene pipes. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A measurement circuit diagram of an embodiment of the present invention;

[0028] Figure 2 This is a diagram of a main control chip and its peripheral circuits according to an embodiment of the present invention;

[0029] Figure 3 This is a current expansion circuit diagram of an embodiment of the present invention;

[0030] Figure 4 This is a parallel resistance circuit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0032] A circuit for measuring the minute resistance of a polyethylene electric fusion pipe fitting comprises a main control chip STM32F103ZET6, a current expansion circuit, a series resistance circuit and a parallel resistance circuit.

[0033] The current expansion circuit includes a first operational amplifier U1, a second operational amplifier U2 and a transistor T1. The output end of the first operational amplifier U1 is electrically connected to the in-phase input end of the second operational amplifier U2, the negative power supply end of the second operational amplifier U2 is grounded, the positive power supply end of the second operational amplifier U2 is connected to the positive power supply 12V, the output end of the second operational amplifier U2 is connected to the base end of the transistor T1, the inverting input end of the second operational amplifier U2 is connected to the connecting line between its output end and the base end of the transistor T1, and the collector end of the transistor T1 is connected to the positive pole of the DC power supply +5V.

[0034] The series resistor circuit is formed by sequentially connecting a third resistor R3, a fourth resistor R4 and a fifth resistor R5 in series, the other end of the third resistor R3 is grounded, and the other end of the fifth resistor R5 is grounded.

[0035] The parallel resistor circuit includes a first connection terminal V1, a second connection terminal V2, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9 and a tenth resistor 10. One end of the sixth resistor R6, the seventh resistor R7, the eighth resistor R8, the ninth resistor R9 and the tenth resistor 10 is connected to the first connection terminal V1, and the other end is connected to the second connection terminal V2. The resistance values ​​of the sixth resistor R6, the seventh resistor R7, the eighth resistor R8, the ninth resistor R9 and the tenth resistor 10 are all 10Ω.

[0036] The DAC module of the main control chip is connected to the in-phase input of the first operational amplifier U1 at its output end to provide a voltage output signal. The second resistor R2 is connected to the connection line between the output of the main control chip and the in-phase input of the first operational amplifier U1.

[0037] The inverting input terminal of the first operational amplifier U1 is connected to the connecting line between the third resistor R3 and the fourth resistor R4, the emitter terminal of the transistor T1 is connected to the first connecting terminal V1 of the parallel resistor circuit, and the third connecting terminal V3 is arranged on the connecting line between the fourth resistor R4 and the fifth resistor R5.

[0038] The three input terminals of the ADC module of the main control chip are respectively connected to the first connection terminal V1, the second connection terminal V2, and the third connection terminal V3, and the voltage values ​​of the three test points are respectively collected and converted to calculate the resistance value to be measured.

[0039] The first connection terminal V1 is connected to the anode of the first diode D1, the cathode of the first diode D1 is connected to the positive electrode of the power supply 3.3V, the second connection terminal V2 is connected to the anode of the second diode D2, the cathode of the second diode D2 is connected to the positive electrode of the power supply 3.3V, the third connection terminal V3 is connected to the anode of the third diode D3, and the cathode of the third diode D3 is connected to the positive electrode of the power supply 3.3V.

[0040] A fourth capacitor C4 is connected to a point on a connection line between the positive power supply terminal of the second operational amplifier U2 and the positive power supply 12V, and the other end of the fourth capacitor C4 is grounded.

[0041] Figure 1 To measure the circuit diagram, the automatic measurement of the tiny resistance of the electric fusion pipe can be realized.

[0042] Figure 2 The main control chip STM32F103ZET6 and its peripheral circuits. The STM32 chip is used to control the automatic measurement of the resistance of the electric fusion pipe fittings in the entire measurement circuit; the peripheral circuits of the STM32 chip include a clock circuit and a reset circuit. The clock circuit provides a reference clock for the normal operation of the STM32 chip, and the reset circuit completes the initialization of the STM32 chip. The DAC module and ADC module of the STM32 chip are mainly used in the measurement circuit design. The DAC module provides input voltage for the measurement circuit, and the ADC module is used to collect the voltage values ​​of the test points V1, V2, and V3 for calculating the resistance value of the electric fusion pipe fittings. The main control chip converts the resistance value to be measured based on the collected three-point voltage values ​​and parallel resistance values.

[0043] Figure 3 It is a current expansion circuit. Among them, the second operational amplifier U2 is a voltage follower with low output impedance, which is equivalent to a constant voltage source for the subsequent circuit and has an isolation effect. When the output voltage of the operational amplifier U2 turns on the transistor T1, T1 amplifies the weak current signal into a current signal with a larger amplitude, thereby achieving the purpose of current expansion. Because the resistance of the pipe to be tested is small, a large current is passed into the voltage divider circuit, which can improve the accuracy of the measurement.

[0044] Figure 4 It is a voltage divider circuit. R6, R7, R8, R9, and R10 are the internal resistors of the measurement circuit. The resistance is 10Ω, and the parallel resistance is 2Ω. Because the current flowing into the voltage divider circuit is a large current signal, multiple resistors need to be connected in parallel to prevent burning. When the resistance of the electric fusion pipe fitting is to be measured, the electric fusion pipe fitting to be measured is connected between the second connection terminal V2 and the third connection terminal V3 of the test point. When the pipe fitting is not measured, the second connection terminal V2 and the third connection terminal V3 of the test point are connected together. The resistance of the electric fusion pipe fitting is calculated by the voltage divider with the internal resistance of the measurement circuit. The voltage divider formula is: The calculation formula for the resistance of electric fusion fittings is: Among them, diodes D1, D2, and D3 play a protective role. When the voltage at the first connection terminal V1, the second connection terminal V2, and the third connection terminal V3 exceeds 3.3V, the diodes are turned on. Since the conduction voltage drop of the diodes is very small, the voltage at points V1, V2, and V3 is clamped at 3.3V.

[0045] The circuit principle of the present invention is further described in detail below.

[0046] In a measurement circuit for the tiny resistance of a polyethylene electric fusion pipe designed by the present invention, the STM32 chip is the main control chip to control the operation of the entire measurement circuit. First, the DAC module of the STM32 chip gives a voltage signal, which flows into the operational amplifier U1 through R2. U1 and its external circuit constitute a common-phase amplifier circuit to amplify the voltage signal output by the DAC module. The output signal of U1 is amplified into a large current signal through the current expansion effect of the U2 and T1 circuits, and flows into the voltage divider circuit. The ADC module of STM32 collects the voltages of the test points V1, V2, and V3. The voltage difference between V1 and V2 is the voltage drop of the internal resistance of the measurement circuit, and the voltage difference between V2 and V3 is the voltage drop on the resistance of the electric fusion pipe to be measured. Through the voltage divider principle, the calculation formula for the resistance of the electric fusion pipe is obtained as follows:

[0047] The invention discloses a circuit for measuring the tiny resistance of a polyethylene electric fusion pipe fitting, which has a measuring range of 0.1Ω-10Ω and basically meets the measurement requirements of the resistance values ​​of all types of electric fusion pipe fittings, and has the characteristics of high measuring precision and accurate measuring, thereby improving the welding quality of polyethylene pipes.

[0048] Among them, R1=10KΩ; R2=1KΩ; R3=R4=300KΩ; R5=10KΩ.

[0049] It is to be understood that although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A circuit for measuring the tiny resistance of polyethylene electric fusion pipe, characterized in that: Including main control chip, current expansion circuit, Series resistor circuits and parallel resistor circuits; The current expansion circuit includes a first operational amplifier U1, a second operational amplifier U2 and a transistor T1, the output end of the first operational amplifier U1 is electrically connected to the in-phase input end of the second operational amplifier U2, the negative power supply end of the second operational amplifier U2 is grounded, the positive power supply end of the second operational amplifier U2 is connected to the positive electrode of the DC power supply, the output end of the second operational amplifier U2 is connected to the base end of the transistor T1, the inverting input end of the second operational amplifier U2 is electrically connected to the connecting line between its output end and the base end of the transistor T1, and the collector end of the transistor T1 is connected to the positive electrode of the DC power supply; The series resistor circuit is formed by connecting a third resistor R3, a fourth resistor R4 and a fifth resistor R5 in series in sequence, the other end of the third resistor R3 is grounded, and the other end of the fifth resistor R5 is grounded; The parallel resistor circuit includes a first connection terminal V1, a second connection terminal V2, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9 and a tenth resistor R10, one end of each of the sixth resistor R6, the seventh resistor R7, the eighth resistor R8, the ninth resistor R9 and the tenth resistor R10 is connected to the first connection terminal V1, and the other end is connected to the second connection terminal V2; The output end of the main control chip is connected to the in-phase input end of the first operational amplifier U1 to provide a voltage output signal; the inverting input end of the first operational amplifier U1 is connected to the connecting line between the third resistor R3 and the fourth resistor R4; the emitter end of the transistor T1 is connected to the first connection end V1 of the parallel resistance circuit; The third connection terminal V3 is arranged on the connection line between the fourth resistor R4 and the fifth resistor R5; The three input terminals of the main control chip are respectively connected to the first connection terminal V1, the second connection terminal V2, and the third connection terminal V3, and the voltage values ​​of the three test points are respectively collected; Connect the electric fusion pipe to be tested between the second connection terminal V2 and the third connection terminal V3 of the test point; The first connection terminal V1 is connected to the anode of the first diode D1, and the cathode of the first diode D1 is connected to the positive electrode of the power supply; The second connection terminal V2 is connected to the anode of the second diode D2, and the cathode of the second diode D2 is connected to the anode of the power supply; The third connection terminal V3 is connected to the anode of the third diode D3, and the cathode of the third diode D3 is connected to the anode of the power supply; A fourth capacitor C4 is connected to a point on a connection line between the positive power supply terminal of the second operational amplifier U2 and the positive power supply 12V, and the other end of the fourth capacitor C4 is grounded.

2. The circuit for measuring the minute resistance of polyethylene electric fusion pipe according to claim 1, characterized in that: The second resistor R2 is connected to the connection line between the output terminal of the main control chip and the in-phase input terminal of the first operational amplifier U1.

3. The circuit for measuring the minute resistance of polyethylene electric fusion pipe according to claim 1, characterized in that: The main control chip is an STM32 chip, the DAC module of which is an output terminal and provides a voltage signal, and the ADC module of which is an input terminal and respectively collects the voltage values ​​of the first connection terminal V1, the second connection terminal V2, and the third connection terminal V3.

4. The circuit for measuring the minute resistance of polyethylene electric fusion pipe according to claim 3, characterized in that: The main control chip is connected with a clock circuit and a reset circuit.

5. The circuit for measuring the minute resistance of polyethylene electric fusion pipe according to claim 1, characterized in that: The resistance values ​​of the sixth resistor R6 , the seventh resistor R7 , the eighth resistor R8 , the ninth resistor R9 and the tenth resistor R10 are all 10Ω.

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