Vacuum closed-loop frequency conversion control system for pipes

Abstract

The utility model relates to a vacuum closed-loop variable-frequency control system for pipes, which comprises a vacuum pump, a contactor, a frequency converter, a pressure transmitter and a pressure controller. The power input end of the frequency converter is connected to a three-phase power supply, and the power output end of the frequency converter is connected to the vacuum pump through a contact of the contactor; the pressure controller is respectively connected with the pressure transmitter and the frequency converter, the pressure controller comprises a voltage division circuit, a first comparison circuit, a second comparison circuit, a first relay, a second relay and a third relay, one end of the voltage division circuit is connected to the output end of the pressure transmitter, and the other end of the voltage division circuit is grounded. Compared with the prior art, the utility model has the advantages that the cost is low, the control precision in an unstable state and under external interference is improved, and the like.

Description

Technical Field

[0001] The utility model relates to the field of a vacuum shaping table for pipes, in particular to a vacuum closed-loop frequency conversion control system for pipes. Background Art

[0002] During the production of pipes, the product needs to be cooled and shaped. In the early days, the vacuum was manually controlled by a pressure relief valve, which required frequent manual operation and often wasted a lot of electricity after normal production. During the production process, if the vacuum was too small, the pipe blank was not easy to shape. If the vacuum was too large, the pipe diameter was too large and it was difficult to ensure qualified products, which wasted raw materials and had high production costs.

[0003] In this regard, technical personnel in this field control the vacuum degree by adopting a closed-loop automatic control method. Generally, the prior art includes a pressure transmitter, a pressure controller and a frequency converter. After the pressure transmitter collects air pressure, it inputs it to the pressure controller. The pressure controller determines whether the pressure collected by the pressure transmitter exceeds a preconfigured threshold value, and then decides whether to start the vacuum pump. In the frequency conversion system, generally, the pressure transmitter outputs a voltage signal to the pressure controller. The greater the pressure (the lower the vacuum degree), the greater the voltage. The frequency converter adjusts the PWM duty cycle according to the size of this voltage, thereby controlling the speed of the motor vacuum pump motor.

[0004] However, in the prior art, since a linear control method is formed depending on the voltage value, if the voltage value is offset, inaccurate speed control may occur easily. When the power supply is unstable or there are too many interfering devices, the control accuracy may be reduced. Utility Model Content

[0005] The purpose of the utility model is to provide a vacuum closed-loop frequency conversion control system for pipes. By adding two comparators and two relays, the analog input is converted into a three-bit digital output, thereby improving the control accuracy under voltage fluctuations and external interference, and compared with the traditional analog-to-digital conversion method, it has the advantages of low cost and high reliability.

[0006] The purpose of the utility model can be achieved through the following technical solutions:

[0007] A vacuum closed-loop variable frequency control system for pipes, comprising a vacuum pump, a contactor, a frequency converter, a pressure transmitter and a pressure controller, wherein the power input end of the frequency converter is connected to a three-phase power supply, and the power output end is connected to the vacuum pump through the contacts of the contactor, and the pressure controller is respectively connected to the pressure transmitter and the frequency converter, and the pressure controller comprises a voltage divider circuit, a first comparison circuit, a second comparison circuit, a first relay, a second relay and a third relay, wherein one end of the voltage divider circuit is connected to the output end of the pressure transmitter, and the other end is grounded.

[0008] The first comparison circuit has a positive input terminal connected to the voltage-dividing output terminal of the voltage-dividing circuit, an inverting input terminal connected to the first reference power supply, an output terminal connected to the coil of the second relay, and a normally open terminal of the second relay connected to the first control signal input terminal of the inverter;

[0009] The non-phase input terminal of the second comparison circuit is connected to the voltage-dividing output terminal of the voltage-dividing circuit, the inverting input terminal is connected to the second reference power supply, the output terminal is connected to the coil of the third relay, and the normally open terminal of the third relay is connected to the second control signal input terminal of the frequency converter, wherein the voltage of the second reference power supply is different from that of the first reference power supply;

[0010] The coil of the first relay is connected to the voltage-dividing output terminal of the voltage-dividing circuit, and the normally open end is connected to the first enabling signal input terminal of the frequency converter.

[0011] The control system also includes a protection relay, the first relay is a double-pole double-throw relay, the normally open end of the first group of contacts of the first relay is connected to the first enable signal input terminal of the inverter, the normally open end of the second group of contacts is connected to the coil of the protection relay, and the normally open end of the protection relay is connected to the coil of the contactor.

[0012] The control system further comprises a first manual switch, which is connected in parallel with a normally open terminal of the protection relay.

[0013] The common end of the first group of contacts of the first relay is connected to the 24V DC output end of the inverter.

[0014] The coil of the contactor is connected in series with a thermal protector.

[0015] A circuit breaker is provided between the frequency converter and the three-phase power supply.

[0016] The control system also includes an alarm, the second relay and the third relay are double-pole double-throw relays,

[0017] The normally open end of the first group of contacts of the second relay is connected to the first control signal input end of the frequency converter;

[0018] The normally open end of the first group of contacts of the third relay is connected to the second control signal input end of the frequency converter;

[0019] The normally open ends of the second contact groups of the second relay and the third relay are both connected to the alarm.

[0020] A second manual switch is provided between the alarm and the second relay and the third relay.

[0021] The alarm is an audible and visual alarm.

[0022] A common terminal of the second relay and the third relay is connected to a low voltage DC power supply.

[0023] Compared with the prior art, the utility model has the following beneficial effects:

[0024] 1. By adding two comparators and two relays, the analog input is converted into a three-bit digital output, which can improve the control accuracy under voltage fluctuations and external interference. Compared with the traditional analog-to-digital conversion method, it has the advantages of low cost and high reliability.

[0025] 2. The output of the first relay also serves as an enable signal, which can reduce the occupation of the inverter input pins, thereby retaining a certain degree of scalability.

[0026] 3. By setting the protection relay as the transition of the enable signal, the pressure transmitter can be effectively protected.

[0027] 4. The contactor coil is connected in series with a thermal protector to achieve thermal protection.

[0028] 5. The problem of frequent alarm operation can be solved by designing the second relay and the third relay as double-pole double-throw relays and connecting the second set of contacts of the two in parallel as the signal to drive the alarm. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the utility model;

[0030] Figure 2 This is a circuit diagram of the secondary side of the pressure controller of the utility model;

[0031] Figure 3 This is the circuit diagram of the contactor part;

[0032] Figure 4 This is the circuit diagram of the alarm part;

[0033] Figure 5 It is a schematic diagram of the primary side of the utility model;

[0034] Among them: 1. vacuum pump, 2. frequency converter, 3. pressure controller, 4. pressure transmitter, K1. first relay, K2. second relay, K3. third relay, K4. protection relay, R1. first resistor, R2. second resistor, R3. third resistor, R4. fourth resistor, R5. fifth resistor, R6. sixth resistor, R7. seventh resistor, U1. first comparison circuit, U2. second comparison circuit, KM. contactor, Vin. output voltage of pressure transmitter, VCC. reference voltage, Vref1. first voltage power supply, Vref2. second reference power supply, S1. first manual switch, FR1. thermal protector, VDD2. low voltage DC power supply, P1. alarm, QF1. circuit breaker. DETAILED DESCRIPTION

[0035] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0036] A vacuum closed-loop variable frequency control system for pipes, such as Figures 1 to 5 As shown, it includes a vacuum pump 1, a contactor KM, a frequency converter 2, a pressure transmitter 4 and a pressure controller 3. The power input end of the frequency converter 2 is connected to a three-phase power supply, and the power output end is connected to the vacuum pump 1 through the contact of the contactor KM. The pressure controller 3 is connected to the pressure transmitter 4 and the frequency converter 2 respectively. The pressure controller 3 includes a voltage divider circuit, a first comparison circuit U1, a second comparison circuit U2, a first relay K1, a second relay K2 and a third relay K3. One end of the voltage divider circuit is connected to the output end of the pressure transmitter 4, and the other end is grounded.

[0037] The first comparison circuit U1 has a positive input terminal connected to the voltage-dividing output terminal of the voltage-dividing circuit, an inverting input terminal connected to the first reference power supply Vref1, an output terminal connected to the coil of the second relay K2, and a normally open terminal of the second relay K2 connected to the first control signal input terminal of the frequency converter 2;

[0038] The non-phase input terminal of the second comparison circuit U2 is connected to the voltage-dividing output terminal of the voltage-dividing circuit, the inverting input terminal is connected to the second reference power supply Vref2, the output terminal is connected to the coil of the third relay K3, and the normally open terminal of the third relay K3 is connected to the second control signal input terminal of the frequency converter 2, wherein the voltage of the second reference power supply Vref2 is different from that of the first reference power supply Vref1;

[0039] The coil of the first relay K1 is connected to the voltage-dividing output terminal of the voltage-dividing circuit, and the normally open end is connected to the first enabling signal input terminal of the frequency converter 2 .

[0040] By adding two comparators and two relays, the analog input is converted into a three-bit digital output, which can improve the control accuracy under voltage fluctuations and external interference. Compared with the traditional analog-to-digital conversion method, it has the advantages of low cost and high reliability.

[0041] Furthermore, the output of the first relay K1 is also used as an enable signal, which can reduce the occupation of the input pin of the inverter 2, thereby retaining a certain degree of expansibility.

[0042] In most embodiments, the control system also includes a protection relay K4, the first relay K1 is a double-pole double-throw relay, the first group of contacts is K1A, the second group of contacts is KAB (not shown), the normally open end of the first group of contacts of the first relay K1 is connected to the first enable signal input terminal of the inverter 2, the common end is connected to the 24V DC output terminal of the inverter 2, the normally open end of the second group of contacts is connected to the coil of the protection relay K4, and the normally open end of the protection relay K4 is connected to the coil of the contactor KM.

[0043] In addition, in some embodiments, the control system further includes a first manual switch S1, which is connected in parallel to the normally open end of the protection relay K4. By setting the protection relay K4 as the transition of the enable signal, the pressure transmitter 4 can be effectively protected.

[0044] When the contactor KM is energized, the power output of the inverter will be transmitted to the vacuum pump. Through the input of the first enable signal input terminal, the first control signal input terminal and the second control signal input terminal, the inverter generates different duty cycles, and the three input terminals obtain 3-bit digital signals in sequence. For example, when the three input terminals are all high level, that is, when the first relay to the third relay are all energized, the obtained digital signal is 111. At this time, the duty cycle of the PWM control signal output by the inverter is the largest, and the vacuum pump works at full speed. Generally, the voltage of the second reference power supply Vref2 is greater than the voltage of the first reference power supply Vref1. As the vacuum degree decreases, the output voltage of the pressure transmitter gradually increases, and as the vacuum degree decreases, the first relay, the second relay and the third relay are energized one by one, so that the duty cycle of the PWM control signal output by the inverter also gradually increases, the maximum is 111, followed by 110, and finally 100. By designing the action current of the first relay and the ratio of the first resistor R1 to the second resistor R2 in the voltage divider circuit, the sensitivity of this control signal can be adjusted.

[0045] Generally, in almost all embodiments, the coil of the contactor KM is connected in series with the thermal protector FR1, and the coil of the contactor KM is connected in series with the thermal protector FR1 to achieve thermal protection.

[0046] In most embodiments, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6 and a seventh resistor R7 are provided to play a current limiting role.

[0047] Under normal circumstances, a circuit breaker QF1 or a fuse is provided between the inverter 2 and the three-phase power supply.

[0048] In addition, in some embodiments, the control system further includes an alarm P1, and the second relay K2 and the third relay K3 are both double-pole double-throw relays. Specifically,

[0049] The normally open end of the first group of contacts of the second relay K2 is connected to the first control signal input end of the frequency converter 2;

[0050] The normally open end of the first group of contacts of the third relay K3 is connected to the second control signal input end of the frequency converter 2;

[0051] The normally open ends of the second contact groups of the second relay K2 and the third relay K3 are both connected to the alarm P1.

[0052] By designing the second relay K2 and the third relay K3 to be double-pole double-throw relays, and connecting the second sets of contacts of the two in parallel as a signal to drive the alarm P1, the problem of frequent operation of the alarm P1 can be solved.

[0053] In some embodiments, a second manual switch is provided between the alarm P1 and the second relay K2 and the third relay K3 , or, in some embodiments, the alarm P1 is an audible and visual alarm.

[0054] A common end of the second relay K2 and the third relay K3 is connected to a low-voltage DC power source VDD2 , which may be 5V or 12V.

[0055] In this embodiment, the pressure transmitter adopts JBYG-BA-E2 and the frequency converter adopts ABB530.

Claims

1. A vacuum closed-loop variable frequency control system for pipes, comprising a vacuum pump, a contactor, a frequency converter, a pressure transmitter and a pressure controller, wherein the power input end of the frequency converter is connected to a three-phase power supply, the power output end is connected to the vacuum pump through the contact of the contactor, and the pressure controller is connected to the pressure transmitter and the frequency converter respectively, characterized in that: The pressure controller comprises a voltage divider circuit, a first comparison circuit, a second comparison circuit, a first relay, a second relay and a third relay, one end of the voltage divider circuit is connected to the output end of the pressure transmitter, and the other end is grounded. The first comparison circuit has a positive input terminal connected to the voltage-dividing output terminal of the voltage-dividing circuit, an inverting input terminal connected to the first reference power supply, an output terminal connected to the coil of the second relay, and a normally open terminal of the second relay connected to the first control signal input terminal of the inverter; The non-phase input terminal of the second comparison circuit is connected to the voltage-dividing output terminal of the voltage-dividing circuit, the inverting input terminal is connected to the second reference power supply, the output terminal is connected to the coil of the third relay, and the normally open terminal of the third relay is connected to the second control signal input terminal of the frequency converter, wherein the voltage of the second reference power supply is different from that of the first reference power supply; The coil of the first relay is connected to the voltage-dividing output terminal of the voltage-dividing circuit, and the normally open end is connected to the first enabling signal input terminal of the frequency converter.

2. A pipe vacuum closed-loop frequency conversion control system according to claim 1, characterized in that: The control system also includes a protection relay, the first relay is a double-pole double-throw relay, the normally open end of the first group of contacts of the first relay is connected to the first enable signal input terminal of the inverter, the normally open end of the second group of contacts is connected to the coil of the protection relay, and the normally open end of the protection relay is connected to the coil of the contactor.

3. A pipe vacuum closed-loop frequency conversion control system according to claim 2, characterized in that: The control system further comprises a first manual switch, which is connected in parallel with a normally open terminal of the protection relay.

4. A vacuum closed-loop variable frequency control system for pipes according to claim 2, characterized in that: The common end of the first group of contacts of the first relay is connected to the 24V DC output end of the inverter.

5. A pipe vacuum closed-loop frequency conversion control system according to claim 1, characterized in that: The coil of the contactor is connected in series with a thermal protector.

6. A vacuum closed-loop variable frequency control system for pipes according to claim 1, characterized in that: A circuit breaker is provided between the frequency converter and the three-phase power supply.

7. A vacuum closed-loop variable frequency control system for pipes according to claim 1, characterized in that: The control system also includes an alarm, the second relay and the third relay are double-pole double-throw relays, The normally open end of the first group of contacts of the second relay is connected to the first control signal input end of the frequency converter; The normally open end of the first group of contacts of the third relay is connected to the second control signal input end of the frequency converter; The normally open ends of the second contact groups of the second relay and the third relay are both connected to the alarm.

8. A vacuum closed-loop variable frequency control system for pipes according to claim 7, characterized in that: A second manual switch is provided between the alarm and the second relay and the third relay.

9. A vacuum closed-loop variable frequency control system for pipes according to claim 7, characterized in that: The alarm is an audible and visual alarm.

10. A vacuum closed-loop variable frequency control system for pipes according to claim 1, characterized in that: A common terminal of the second relay and the third relay is connected to a low voltage DC power supply.

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