Application of digital technology for electrical isolation sensor
I. Overview The power isolation sensor transmitter is a small-volume, high-performance power test component (product) developed for power detection (monitoring) in the project to improve the overall anti-interference ability of the system. The electric quantity isolation sensor transmitter can measure and transform the electric parameters such as large current, high voltage, power, frequency, phase angle, electric degree, etc. on the spot, and can also perform various weak signals (such as various bridge signals) Isolate, amplify and transform, and after conditioning, transform into analog signals such as voltage, current, frequency, etc. that comply with international standards or transform into digital and digital output signals. These output signals can be connected with traditional pointer instruments, and also directly connected with modern digital automatic control instruments, various AD converters and computer systems, so as to form a highly reliable industrial detection (monitoring) or control system. As the battery isolation sensor is applied, the user does not need to do secondary development work. High-voltage or high-current signals can be directly connected to the product (input through terminals, pin input or perforation), and the corresponding output signal can be obtained. Therefore, as the signal conditioning, isolation and transformation function block, the power isolation sensor is an ideal transmitter product in industrial control and data acquisition systems. With the continuous development of science and technology, industrial control or detection (monitoring) systems have increasingly higher requirements for electrical isolation sensors, especially in terms of product stability, detection accuracy and function. Because of the performance or function of digital products, such as non-linear correction and small signal processing, analog products are incomparable. Therefore, the digitization of electrical isolation sensors is an inevitable trend. The following is a brief description of the working principle of the electrical isolation sensor and its digital technology for your reference. Second, the basic working principle of power isolation sensor Since the detected objects of the power isolation sensor products are mainly current and voltage signals, the following mainly introduces the detection principles of current and voltage signals. 1. AC signal detection principle AC signals are divided into AC voltage and current signals. Figure 1 is a block diagram of the detection principle of the AC current signal. Figure 2 is a block diagram of the detection principle of the AC voltage signal. The signals are isolated by CT and PT, the current is the perforated input mode, and the voltage is the terminal wiring input mode. Figure 1 Block diagram of AC current signal detection Figure 2 Principle block diagram of AC voltage signal detection Among them, CT is the current transformer, PT is the voltage transformer, the output is generally 0 ~ 5V or 4 ~ 20mA. 2. Principle of DC signal detection Figure 3 Block diagram of DC signal detection The DC signal is divided into DC voltage and DC current. The DC current is generally sampled by a resistor, and the DC voltage is generally processed by a resistor step-down. An isolated power supply supplies power to the preamplifier. It can be seen from the above principle block diagram, whether it is AC signal or DC signal, the input and output are completely isolated. Generally, the field input signal is high current or high voltage, so that the power isolation sensor can collect the field signal and low voltage data. The system is completely isolated to prevent the system from being interfered by strong signals, thereby improving the reliability of the system. 3. Digital technology of power isolation sensor Figure 4 is a combined block diagram of an AC signal digital power isolation sensor, which is composed of transformers, data processing, interfaces, TV conversion and output. Figure 4 AC signal digital power isolation sensor combination block diagram . There are two kinds of current transformers and voltage transformers. Current transformers are generally perforated, and voltage transformers generally need to add current limiting resistors on their primary sides; . The data processing part is the core part of product digitization. At present, the single chip microcomputer with AD converter is generally selected, such as PIC16C74, MSP430 or ADCUC812. Therefore, the circuit can be very simple. If you choose ADUC812 MCU, you can directly output 0 ~ 5V voltage signal, because it contains two 12-bit DA converters; . The interface part is a conversion circuit for digital signal output. At present, the RS-485 bus interface is widely used. The most commonly used interface chip is ADM483. It can connect up to 32 nodes. Of course, there are many other similar chips. The RS-232 interface is generally implemented in two ways. One is to add an RS-485 RS-232 converter to the RS-485 network bus, and the other is to directly put the RS-232 interface chip in the product. The shortcoming of this kind is that the application of the product will be restricted, can not form a network structure, only point-to-point communication. CAN-BUS is a bus that is developing rapidly at present. Its advantage is that the transmission distance is long, and it can reach 10km. There will be no bus conflicts, multi-master working mode, good communication protocol universality, and of course its higher cost. . TV conversion is to be compatible with the analog signal acquisition and input system. Currently, PWM is generally used for output, and then TV conversion is performed to output 0 to 5V or 4 to 20mA analog signals. . The software mainly contains three functional modules, data acquisition, data processing and communication protocol. Among them, the data collection is mainly to read the conversion result of AD, because the microcontroller comes with AD, so the program is relatively simple; . Data processing mainly completes the operation of AC to DC. Due to the limited operation speed of single chip microcomputer, we use frequency tracking method to complete the calculation of conversion; The communication protocol is generally selected by the user, such as MODBUS protocol, ASCII format, etc. 4. Conclusion The above briefly introduces the basic working principle and digital technical issues of the electrical isolation sensor. Since the digital power isolation sensor can directly output the digital quantity, the AD acquisition module can be omitted for many application systems, so the system cost can be reduced. Therefore, the digitization of power isolation sensors not only improves product stability, but also enables users to further reduce costs. Because there are many types of battery isolation sensors, this article only introduces a digital technology of AC signal battery isolation sensors. There are many ways to realize the digitization of the battery isolation sensor. At present, the most common one is the use of single-chip technology, because its application is very flexible and can achieve a variety of different functions. With the continuous development of integrated circuits, many special chips have appeared, such as watt-hour meter products. There are many special chips available, with digital interfaces and pulse outputs. This article has made a superficial discussion on the digitalization of the electrical isolation sensor products, which is only for the reference of relevant personnel, and hopes to play a role in inspiring others and accelerate the greater development of the digital technology of electrical isolation sensors. Cob Lights ,Cob Led Strip,Cob Led Light,Cob Strip Light Guangzhou Cheng Wen Photoelectric Technology Co., Ltd. , https://www.cwledwall.com