FBM240 Foxboro DCS Card, Shanghai Sijian Intelligent Technology Co., Ltd. is engaged in technology development, technical consulting, technology transfer in the fields of intelligent technology, information technology, and automation technology, as well as the sales of electrical equipment, automation equipment, electronic products, communication products, and electromechanical products. Industrial automation products include: PLC, DCS, sensors, frequency converters, encoders, relays, servo drives, soft starters, and touch screens. The brands involved in the products are: Eurotherm, Schneider, Siemens, ABB, SICK, P+F, E+H, Yokogawa, Yamakawa, Mitsubishi, Emerson, Honeywell, FANUC, GE, Eaton Electrical, CT. Frequency converters first rectify the mains AC power into DC power, and then the inverter, under the control of a microcontroller, converts the DC power into AC power of varying frequencies.
FBM240 Foxboro DCS Card, Currently, all frequency converters on the market operate based on this working principle. Among them, R0 serves a current-limiting function; when power is applied to the R, S, and T terminals, R0 is connected to the circuit to limit the starting current. After a period of time, the thyristor VT conducts, short-circuiting R0 to avoid unnecessary losses. Rt is the energy consumption braking resistor. During braking, the motor enters a power generation state, and the inverter reversely charges capacitor C. When the voltage in the DC circuit (the voltage across resistors R1 and R2) rises to a certain value, the switching device Vb is turned on via the pump-up circuit, so that the electrical energy on capacitor C is dissipated through resistor Rt. Typically, for heat dissipation, the braking resistor Rt is installed externally to the frequency converter or equipped with a braking unit. Besides participating in braking, capacitor C primarily serves a filtering function during motor operation. Frequency converters that use capacitors for filtering are called voltage-type frequency converters, while those that use inductors for filtering are called current-type frequency converters. Voltage-type frequency converters are more common in the market.
The microcontroller calculates and outputs a sinusoidal control signal, which is modulated by an SPWM (Sinusoidal Pulse Width Modulation) generator, then amplified by the drive circuit. The amplified signal drives six power transistors to generate three-phase AC voltages U, V, and W, which drive the motor to operate. Electrical control systems use the action of time relays for time control, but the timing of time relays is easily affected by changes in ambient temperature and humidity, resulting in low timing accuracy. In contrast, DCS uses semiconductor integrated circuits as timers, with clock pulses generated by crystal oscillators, offering high precision and a wide timing range. Users can set timing values in the program as needed, making modifications convenient and unaffected by environmental influences. Additionally, DCS has counting functions, whereas electrical control systems generally do not.
For the power supply of PLCs, except when introducing equipment along with the PLC where planning and selection should follow the product manual requirements, generally, the power supply for PLCs should be planned and selected as 220VAC, consistent with the domestic grid voltage. For critical applications, an uninterruptible power supply or regulated power supply should be used. If the PLC itself comes with a usable power supply, it is necessary to verify whether the supplied current meets the usage requirements; otherwise, an external power supply should be planned. To prevent external high-voltage power from being mistakenly introduced into the PLC due to misoperation, isolation of input and output signals is necessary. Sometimes, simple diodes or fuse tubes can also be used for isolation.
Selection of memory: Due to advancements in computer integrated chip technology, the price of memory has decreased. Therefore, to ensure the normal operation of the application project, it is generally required that the memory capacity of the PLC be selected as at least 8K for 256 I/O points. When complex control functions are required, a larger capacity and higher-grade memory should be selected.