Design and application of the measurement and control device based on the short circuit fault of the electric heater

At present, fully automatic packaging machines, bag making machines, plastic injection molding machines and other equipment all require electric heaters to package plastic products. The burning out (circuit break) of electric heaters is the most common fault in the use of equipment. Once the electric heater has a circuit break, if it is not eliminated in time, the quality of the plastic formed product cannot be guaranteed at the least, and the raw materials will be wasted at the worst, increasing the operating costs of the enterprise. This technology and patented product can correctly determine whether the electric heater is automatically powered off due to temperature rise or the electric heater has a circuit break.

1 Research significance of the device
The research significance of the device mainly comes from related equipment manufacturers (such as packaging machinery, bag making machinery, injection molding machinery, etc.) and direct product application enterprises. The production processes of these enterprises show that:
(1) Electric heating equipment has a wide application market in the packaging industry.
(2) Electric heater burnout (circuit break) is the most common fault in the use of equipment.
(3) If the electric heater burnout fault is not eliminated in time, the product quality of the plastic molded product cannot be guaranteed at the least, and it will cause waste of raw materials, loss of manpower and material resources, and increase the operating costs of the enterprise.
In response to the needs of the plastic packaging processing industry, the device should meet the following requirements:
(1) The electric heater circuit break detection device can automatically identify the temperature rise heater power failure and electric heater circuit break fault.
(2) After the electric heater circuit break, the processing machine is immediately controlled to stop running and an alarm signal is given.

2 Background of the device
China is a major packaging manufacturing and consumption country in the world. Since the 1990s, due to the needs of the development of the packaging products industry, it has developed rapidly, with an average annual growth rate of 30%. The proportion of plastic packaging in the total output value of the packaging industry has exceeded 30%, becoming a new force in the packaging industry, playing an irreplaceable role in food plastic packaging, medical plastic packaging, cosmetics plastic packaging, pesticide plastic packaging and various fields of industrial and agricultural production. At present, the output of domestic packaging machines, bag making machines, injection molding machines and other electric heating machinery and equipment will increase significantly, but the service life of its electric heater is only 2 to 3 months. Once the heater burns out, it will cause a waste of raw materials and affect the product quality.
2.1 Key technology
The electric heater on the packaging machine is generally controlled by the contacts of the temperature control instrument to control the AC power supply on and off. When the temperature of the electric heater is lower than the set temperature, the contacts of the temperature control instrument are connected, and the temperature of the electric heater rises. When the temperature of the electric heater is higher than the set temperature, the contacts of the temperature control instrument are disconnected, and the temperature of the electric heater drops. The contacts of the temperature control instrument are turned on and off to ensure that the electric heater works within a certain temperature range. Once the heater burns out, the operator cannot determine whether the heater is powered off normally due to the temperature rise or the heater circuit breaker fault. Due to the thermal inertia of the heater, the temperature needs to be delayed for a period of time before it drops. In this way, when the operator finds that the product is unqualified, hundreds of thousands of products have been wasted, affecting the product quality. The electric heater circuit breaker detection device should be able to automatically identify the temperature rise heater power failure and the electric heater circuit breaker fault.
2.2 Existing technical conditions at home and abroad
At present, foreign intelligent temperature control instruments have both low temperature detection and alarm functions, but no heater circuit breaker fault detection, such as Fuji and Omron products in Japan; related products produced by some domestic enterprises are large in size, complex in detection and alarm configuration, poor in reliability, and inconvenient to install and maintain, which cannot meet the needs of related enterprises well.
2.3 The market demand is large, requiring the technical product to be cost-effective and easy to install
At present, the output of domestic packaging machines, bag making machines, injection molding machines and other electric heating machinery and equipment has increased significantly, and most of the users are small and medium-sized enterprises. Due to the fierce market competition, especially the direct users of plastic processing machinery forming products need electric heater circuit breaker fault measurement and control devices with low product price, reliable performance, easy installation and maintenance to ensure the quality of plastic packaging machinery forming products.

3 Working principle of the device
The electric heater circuit breaker fault measurement and control device is connected in series between the heater and the temperature control instrument contacts, and mainly uses the current detection of the heater circuit breaker (burnout) and the voltage detection of the instrument contact switch point K. If the instrument contact K is normally on and off, there is no effect on this device and no signal output; only when the heater has a circuit breaker fault, this device will have a signal output, and then cooperate with other devices (display, buzzer, host control, etc.) to achieve the control function requirements.

The schematic diagram of the system configuration is shown in Figure 1. The packaging machine electric heater disconnection measurement and control device consists of a contact action detection circuit, a heater fault detection circuit, a measurement and control signal output circuit and a DC power supply; the horizontal seal contact action detection circuit and the vertical seal contact action detection circuit are respectively connected to the two ends of the horizontal seal temperature control instrument contact switch (K1) and the vertical seal temperature control instrument contact switch (K2) to detect the voltage at the instrument contact switch. When the contact switches K1 and K2 are disconnected, the light-emitting diodes L1 and L2 emit light; when the contact switches K1 and K2 are closed, the light-emitting diodes L3 and L4 emit light. The horizontal seal (vertical seal) heater fault detection circuit is connected in series between the horizontal seal (vertical seal) heater and the temperature control instrument contact switch K1 (K2) to detect the current of the horizontal seal (vertical seal) heater disconnection; when the heater is normal, the light-emitting diode L5 (L6) does not emit light; when the horizontal seal (vertical seal) heater is disconnected, the light-emitting diode L5 (L6) emits light to alarm; at the same time, the relay J is energized to give a control signal to the outside. As shown in Figure 2.

The packaging machine is generally composed of a horizontal sealing heating circuit and a vertical sealing heating circuit. The two circuit structures are the same, so only the horizontal sealing heating circuit is analyzed. The horizontal sealing contact action detection circuit includes resistors (R1, R2), rectifier diodes (D1), filter capacitors (C1), photoelectric coupling devices TLP521-1 (U1) and LED light-emitting diodes (L1). When the contact switch (K1) is disconnected, the LED light-emitting diode (L1) emits light; the photoelectric coupling device (U1) outputs a low level, and the transistors (Q3, Q5) of the measurement and control signal output circuit are cut off; when the contact switch (K1) is closed, the LED light-emitting diode (L1) does not emit light, the photoelectric coupling device (U1) outputs a high level, the diode (D9) is cut off, the transistor (Q1) is turned on, the LED light-emitting diode (L3) emits light, the clamping diode (D10) is turned on, and the transistors (Q3, Q5) of the measurement and control signal output circuit are cut off.
According to Faraday's law of electromagnetic induction, as long as the magnetic flux linked by the coil changes, an induced electromotive force will be generated in the coil, regardless of whether the linked magnetic flux is generated by the current of the coil. Therefore, the fault detection circuit of the horizontal seal heater is completed by a mutual inductance circuit, including a mutual inductor (H1), a rectifier diode (D2), a filter circuit capacitor (C2), and a resistor (R4). Transistor (Q1), LED (L3) and dual-channel voltage comparator LM393 (U3); resistors (R9, R10) form a voltage divider circuit to provide a 1 V reference voltage for the voltage comparator (U3); when the horizontal seal heater is normal, the LED (L3) lights up, indicating that the horizontal seal contact switch K1 is closed, the voltage comparator (U3) outputs a high level, the transistor (Q1) is turned on, the clamping diode (D10) is turned on, the horizontal seal heating circuit indicator LED (L5) does not light up, the output drive circuit transistors (Q3, Q5) are turned off, and there is no output to the outside; when the horizontal seal heater is disconnected, there is no induced voltage on the current detection transformer (H1), the voltage comparator (U3) outputs a low level, the transistor (Q1) is turned off, the measurement and control signal output circuit transistors (Q3, Q5) are turned on, and the light emitting diode (L5) lights up to alarm; at the same time, the relay (J) is energized to give a control signal to the outside.
The power module uses a three-terminal integrated voltage regulator, which includes various components of series DC voltage regulation, plus protection circuit and startup circuit. In the W7800 series three-terminal integrated voltage regulator, three protection circuits have been integrated into the chip, which are current limiting protection circuit, overheat protection circuit and overvoltage protection circuit.

The DC voltage regulator circuit is composed of a transformer (H3), a rectifier diode (D5-D8), a filter capacitor (C5, C6) and a three-terminal voltage regulator W7812 (U4), which provides a 12 V DC voltage for the circuit breaker measurement and control device.
The main considerations in the design of the electric heater circuit breaker fault measurement and control device are:
(1) In the actual electronic circuit system, various interference signals are inevitably present. If the circuit has poor anti-interference ability, it will lead to reduced measurement and control accuracy, resulting in malfunctions, which will bring destructive consequences. If some design techniques are used in the hardware to destroy the path of interference signals entering the measurement and control system, the anti-interference ability of the system can be effectively improved. The use of isolation technology is a simple and effective method. Isolation technology is an anti-interference method that destroys the "ground" interference path. Optoelectronic coupling devices are often used in hardware to achieve electrical-optical-electrical isolation. It can effectively destroy the entry of interference sources and reliably achieve signal isolation. Therefore, optoelectronic isolation technology is used in the input/output circuit to ensure the isolation between strong and weak electricity and the series entry of interference.
(2) Independent appearance structure and clear signal input/output terminals ensure safe and quick installation and maintenance.
(3) The main engine stops running immediately after the electric heater is disconnected. After repeated tests and debugging, the product is shown in Figure 3.

4 Application of patent transformation results
The device has applied for a utility model patent, patent number: ZL20072 0096249.2, patent name: Packaging machine heater circuit breaker measurement and control device. The "electric heater circuit breaker fault measurement and control device" developed by Tianjin Electronic Information Vocational and Technical College has been organized for production by Tianjin Fuhang Instrument New Technology Industry Co., Ltd. and is used in conjunction with the electric heater control system in the packaging machinery industry.
This project is a Tianjin Higher Education Science and Technology Development Fund Project, project name: Electric Heater Circuit breaker Fault Measurement and Control Device, project number: 20060617, and has passed the expert acceptance and completion in July 2008.

5 Conclusion
As a supporting component of related equipment, this utility model device has heater disconnection detection, and quickly alarms and outputs after the heater disconnects, quickly stops the operation of the host, and does not waste plastic forming materials after the fault occurs, reduces industrial production costs, and ensures product quality. After one year of use, the product has a reasonable structural design, ingenious circuit design, low cost, and reliable performance. Especially for the modification and installation of old packaging machinery, it is convenient and flexible, and has achieved good economic and social benefits.
Innovation: The device can accurately determine whether the electric heater is automatically powered off due to temperature increase or the electric heater is disconnected, which completely solves the problem of detecting the disconnection of the electric heater in the packaging industry.