With the continuous growth of China's steel production, replacing manual welding with high-efficiency gas shielded welding has become an inevitable trend. At present, the main representatives of all digital multifunctional welding power supplies in the world are: the TPR series Florius, Aristol's Kempi Pro series, and Aristo's ESAB series. The Fronius TPS series was launched in 1998. The main control is simenses c167 plus ad DSP. The wire feeder is controlled by a Siemens microcontroller. Various processes and peripheral devices, including PWM waveforms, are implemented digitally instead of using special PWM ICs. Fronius forms a LAN with rich interfaces. The main disadvantage is that adjusting the parameters on the wire feeder is very inconvenient, and some wire feeders are not displayed, and the panel design does not fully consider the need for welding material expansion.

Kempi Pro mainly uses two 80C196KCs to control the wire feeder and power supply respectively. This panel is connected to the control board of the wire feeder through a common grounding signal line, making it easy to adjust, but not suitable for remote control. Due to further expansion of its usage functions, this interface is not as rich as Fronius. At present, there have been no reports from other manufacturers except for multifunctional digital welding power supplies controlled by microcontrollers. For example, in the welding of pressure pipes in the Three Gorges, manual welding is used for the overlap of circumferential seams, while CO2 welding for short-circuit transition is used for the support of longitudinal seams. In order to meet the needs of automatic welding, pulse welding is used for filling and covering. Usually, various types of welding power sources are required to meet the demand, and the investment is very large.

If a multifunctional welding power supply is used, one device can complete all functions. This can save investment and improve work efficiency. With the improvement of processing speed of high-performance embedded microprocessors, real-time control of high-frequency inverter welding power supplies has become possible. Compared with traditional analog control, digital control has the following advantages:

① Multiple welding processes can be implemented on the same machine;

② Good parameter consistency reduces the number of adjustable potentiometers and eliminates temperature drift in operational amplifiers. The impact on the overall system performance,

③ The system is easy to upgrade, such as adding new welding materials and welding processes;

④ The interface is rich and can meet more application scenarios. If there is a robot interface, an automatic welding system with a remote control port can be formed, which can be remotely controlled and convenient for workers to operate.

⑤ More complex control algorithms can be applied in welding power sources, such as fuzzy control and adaptive control in applications with uniform penetration and constant arc length, which can further improve the machining performance of arc welding power sources.

⑥ The database of welding experts can be easily ported to digital control platforms, and the welding process can be adjusted based on the experience of welding experts, simplifying the operation of welding machines and enabling untrained ordinary welders to become "welding" personnel. Expert.

Requirements for current sensors in digital welding machines

The digital multifunctional welding power platform discussed in this article focuses on five welding processes, namely manual welding, argon arc welding, CO2 MAG welding, pulse MIG welding, and double pulse MIG welding. The first two welding processes are constant current, while CO2 MAG welding is constant voltage, and pulse welding is quasi constant current. No matter which welding process is used, accurate detection of welding current is required, and the detection accuracy should reach 1A level. In TIG welding, due to the impact of the contact arc, the smaller the arc current, the more effective it is in preventing tungsten electrode combustion. The optimal impulse current should be less than 5A. In CO2 MAG welding, accurately detecting the output current is a key factor for the stable operation of the control system in order to accurately determine the arc and short circuit processes.

In pulse MIG welding, during low current welding, the base current of the 1.2mm carbon steel wire is only 20A, and the voltage signal corresponding to this current is less than 100mV. If the detection is inaccurate, the heat input cannot be controlled, which may lead to incomplete fusion or burning through. In gas shielded arc welding, not only is the steady-state accuracy of the welding current required, but also dynamic performance is required. In the process of sudden load changes, the current needs to have fast tracking ability, and the response speed of the current sensor is required to be very high.

In a fully digital welding power supply, a digital encoder is used instead of a potentiometer. The traditional potentiometer can only provide a trend of transformation, while the digital encoder directly provides a digital quantity, which is used as the digital quantity in the control system. Although it is convenient for users, it puts higher requirements on the linearity of the sensor. At the same time, with the improvement of processing speed of embedded microprocessors, in order to reduce power consumption, it is necessary to lower the power supply voltage, which poses new challenges to the power supply and A/D conversion accuracy of the control board.

For example, TI's 240x and 28x series are both powered by 3.3V. Taking a 400A gas shielded welding power supply as an example, considering that its peak current can reach 700A during short circuit or high current arc ignition, such as in the operation of Fronius special aluminum welding four parts, the arc ignition current reaches 750A. If 750A is considered to correspond to the maximum value of digital conversion, then in a 10 bit AD converter, the digital quantity corresponding to 750A is 1024, and the analog voltage output by the current sensor is 3.3V, then the analog voltage corresponding to 20A output is 88mV. This signal is very weak, so there are high requirements for the signal-to-noise ratio of the current sensor.

In summary, in the digital welding power supply, the current sensor, as a key testing equipment, mainly needs to meet the following requirements: ① a wide input current range; ② Good linearity; ③ Fast dynamic response capability; ④ High signal-to-noise ratio.

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